Axial Lighting

[styxman]

My first attempt at axial lighting. Needs a lot of work. The coin has an iridescent sheen which can be clearly seen in the images. Please let me know what you think. I’ll continue to post photos as I improve the system.

Thanks much for all your comments and advice.

Over and out, styxman

[jfines69]

Those pics came out really good... A little glare is all I can tell... Nice coin also!!!

[duece2seven]

Looks pretty good all in all but it's a little dark to me. You certainly picked a tough coin to practice on! :). I can tell the glare on this one
must be a beast to tame on top of trying to balance out the luster with all the rainbow coloring. Also, it seems the coin is tilted a bit from
east to west if that's significant to you. I'd brighten it up a little first and go from there. Nice DDO, btw!

Tracy

[kloccwork419]

What exactly are you using?

[styxman]

Axial Lighting is a technique used in micro-photography and forensic photography. (Please see the attached diagram.) It involves three primary objects. One is a photocopier stand with a camera mounted on it pointing down towards the base of the stand. Second is a variable intensity light source that is off to one side of the photocopier stand. Third is a sheet of regular glass that is positioned directly underneath the camera about midway between the lens and the base of the copier stand and held at 45° from the light source. The light emitting from the source strikes the glass and mostly passes through. However, some of the light is reflected down towards the base of the copier stand. An object (coin) is then placed on the copier stand directly below the camera and the sheet of glass. This is essentially “a light through the lens” technique. If done properly (which I have not achieved) it should yield a uniform distribution of light across the object. Additionally, one can photograph down tubes and hollow objects as light will penetrate down the hole.

As you have noted in the comments, my coins appear dark. This is due to an adequate light source. I have ordered a new one that should be substantially brighter. Additionally, I am still getting some shadows and non-uniform distribution of light from my setup. Not sure why. I will continue working on it and keep you posted.

Thank you for all your comments and ideas. They have been very helpful.

Over and out, styxman

PS Thanks to Ray Parkhurst, I have made a correction to the diagram as shown below. Thanks Ray!

[VAB2013]

Styxman, I think your photos are great! And this technique is outstanding! What you guys do with photos is a work of art! One day I want to be a good photographer!

[ray_parkhurst]

Styxman...one thing not shown in the diagram is a "light blocker" to keep direct light from the light source from hitting the coin. Only reflected light should hit the coin...Ray

[kloccwork419]

I knew the process, I was asking what are you using for it.

[styxman]

Sorry klockwork419 - did not understand your question. In an attempt to correct my bad, here is a list of what I have put together:

Photocopier Stand - Testrite CS-3 Photocopier Stand (Really old)
Camera - Nikon D7000
Lens - Nikon AF-S VR Micro-Nikkor 105mm f/2.8G IF-ED N
Light - Dream Lighting 12 volt DC Down Light (Inadequate)
Power Supply - Dr. Meter HY3005F-3 with three independent output ports with variable voltage and current
Stands - Pipe flange screwed into a piece of wood with PVC piping
Clamp - Old basic spring clamps that bite into the PVC pipe and will also hold the glass and light (Inadequate as the clamps slip over time - not sure what to do)
Light Barrier - 6 inch ID Black PVC pipe cut to length and split in half (forming a half circle making them free standing)

I have ordered a 12 volt DC flood light GLW 10 watt from Amazon, but have not received it yet. (http://www.amazon.com/gp/product/B008XZAQDU?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00)
Not sure if it will work or not. I suspect I will need to place "blinders" on the sides of the light to cut down the spread.

I will attached a new diagram which reflects the mistake I made in leaving out the light barrier as noted by Ray Parkhurst.

I hope this will answer your question. If I have still missed the mark, please let me know!

Over and out, styxman

[ray_parkhurst]

Key to minimizing the effect of the reflector glass causing distortion to the image, the thinner the reflector glass, the better. Most folks will move the light around, or if they have made the glass movable they might change the angle a little, to optimize the way the light hits the coin. Generally the "bigger" the light source, the better for casting a wide, non-shadowing illumination. In my axial setup I use a diffuser in front of the light blocker to increase the apparent size of the light source. If you use a small light source, the light will only come directly from the axial center (true axial) and the resulting image will be very high contrast, with very dark edges to the devices on the coin.

[styxman]

Ray,

Thanks much for all the advise and information. Not sure where to get thin glass - will have to hunt around some. Will try the major hardware chains or, if I can find one, a glass repair store. I have done tons of stained glass, never seen any thin glass in the stained glass suppliers.

The light I ordered is a rectangular flood light reported to replace an 80 watt halogen light - 2700-3200k warm white super bright, shadow-free. Will see.

Thanks again for all your assistance.

Over and out, styxman

[jfines69]

Ray,

Thanks much for all the advise and information. Not sure where to get thin glass - will have to hunt around some. Will try the major hardware chains or, if I can find one, a glass repair store. I have done tons of stained glass, never seen any thin glass in the stained glass suppliers.

The light I ordered is a rectangular flood light reported to replace an 80 watt halogen light - 2700-3200k warm white super bright, shadow-free. Will see.

Thanks again for all your assistance.

Over and out, styxman
Glass from a picture frame should be thin enough???

[ray_parkhurst]

Glass from a picture frame should be thin enough???

Usually picture frame glass is not great quality. It varies a lot in thickness, which will cause distortion. I have used it before and had "OK" results, so it will get you started until you find thin optical glass.

One thing to note is the glass does not have to be very big. A 3"x5" piece will work well, in fact is bigger than needed. For "true axial" the glass just needs to be a little bigger than the coin. But to get reflection off a wider range of angles with a larger light source, 3"x5" is good.

[jfines69]

Usually picture frame glass is not great quality. It varies a lot in thickness, which will cause distortion. I have used it before and had "OK" results, so it will get you started until you find thin optical glass.

One thing to note is the glass does not have to be very big. A 3"x5" piece will work well, in fact is bigger than needed. For "true axial" the glass just needs to be a little bigger than the coin. But to get reflection off a wider range of angles with a larger light source, 3"x5" is good.
I thought the picture frame glass was of better quality... So much for what I know :LOL_Hair: Safety glass would cause distortion also??? Use to be able to get glass from hardware stores like ACE or would it need to be from a specialty supply such as optical glass???

[ray_parkhurst]

Optical glass is probably best. For Cents, I have used blank microscope slides. For variety shots, I've even used coverslips. They are very thin and very uniform.

[styxman]

Thanks everyone! VAB2013 - my pictures suck compared to Ray - look at his web site for some great photos www.macrocoins.com.

I have ordered a 8 X 8 piece of glass 2mm thick from eBay for under $20 - http://www.ebay.com/itm/361030956400?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Hopefully it will be uniform. I will cut it down to 4 X 4 to use with my setup. I will take some pictures of the system once all the pieces have arrived and it is working OK.

Thanks all!

Over and out, styxman

[stoneman227]

Here is a link to Surplus Shed . Absolutely tons of optical fun stuff at ridiculously low prices.

John

http://www.surplusshed.com/

[styxman]

John,

Thanks for the link. What an amazing site! You are correct - tons of stuff. I ordered some Optical Glass Round Window 25 mm Diameter, 1.92 mm Thick (Thin!):
http://www.surplusshed.com/pages/item/l13634.html

It was with a heavy heart and great sorrow that I passed on the purchase of the Ant Farm Live Ant Habitat
http://www.surplusshed.com/pages/item/m6931.html

Wow do they have "STUFF"!

Thanks again. I hope the small glass discs will work in my axial setup. Will keep you posted.

Over and out, styxman

[Roller]

I'm experimenting with the axial set up and getting very frustrated. Does it matter that I have the glass attached to one 45* leg of a 90* steel angle and have it going from SE to NW instead of coming from the side opposite from the light source? And how does one clean the glass so there are absolutely no streaks?

[jfines69]

And how does one clean the glass so there are absolutely no streaks?
Very carefully :LOL_Hair: You can use newspaper to rub it down after cleaning... It removes the streaks!!!

[ray_parkhurst]

I use a piece of chamois.

[styxman]

Roller,

This Axial Lighting is a lot harder than it seems. A couple of things. I found that the light should travel across the coin before hitting the glass. The wrong way is shown in the attached image "Axial_Lighting_Wrong". If the light hits the glass first, as shown in the diagram, I got all kinds of reflections and glare. The light should travel past the coin, strike the glass and then reflected down onto the coin. Secondly, I get better results if the glass is a few degrees off 45 degrees. There seems to be fewer glare spots with the angle slightly off 45 degrees. Not sure if this will help.

As far as cleaning, I use a piece of Microfiber cloth:

http://www.amazon.com/Pack-MagicFiber-Microfiber-Cleaning-Cloths/dp/B0050R67U0/ref=sr_1_1?ie=UTF8&qid=1457059373&sr=8-1&keywords=magic+fiber+cleaning+cloth

This works great and does not leave streaks.

I have yet to find a light bright enough to get my shutter speed down to something manageable. My setup is not well founded and shakes if I sneeze or walk anywhere near the Photo Copy Stand. I am trying some halogen lights – will let you know if I find something that works. Please let us know what is and what isn’t working for you. Pictures would be nice.

I will keep you posted.

Over and out, styxman

[stoneman227]

And how does one clean the glass so there are absolutely no streaks?

I use ROR as a cleaning solution http://www.amazon.com/ROR-Optical-Cleaner-Spray-Bottle/dp/B0002HMRF2
and Kimwipes http://www.edmundoptics.com/lab-production/cleaning/lens-tissue-cloth/kimberly-clark-precision-wipes-kimwipes-ex-l/1504/ to wipe with. I have found the ROR gets any oil off then a bit of breath wiped off gets any residual ROR.

John

[stoneman227]

I have yet to find a light bright enough to get my shutter speed down to something manageable. My setup is not well founded and shakes if I sneeze or walk anywhere near the Photo Copy Stand. I am trying some halogen lights – will let you know if I find something that works.

Honestly, instead of working to find a brighter light your time would be better spent making your copy stand rock solid. If the coin sets on the base of your copy stand then not only is the camera vibrating from the mirror slap, your coin is too. I at times use exposures up to 1second because it can be darned near impossible to control so much glare from a intense light source.

John

[styxman]

John,

I have ordered a bottle of the ROR - sounds very promising. And you are correct about the copier stand. My “working table” is just a shelf on some old wire racks – very unstable no matter how solid the stand. Additionally, my camera is old with a limit of 1/30 sec as the longest exposure. I have ordered a DSUSB from Shoestring Astronomy to link my tethering software to the camera so I can set the exposure time to whatever I want.

http://www.store.shoestringastronomy.com/products_ds.htm

I have set a 50 millisecond pause between the mirror lift and the exposure. This is something that I might lengthen to see if the system quiets down and stops vibrating. Still lots to explore.

Thanks for the link for the ROR.

Over and out, styxman

[ray_parkhurst]

You guys are linking to some cool stuff!

[silver1985]

I'm trying to visualize (in my mind) what the effect axial lighting would have on showing cartwheel luster and small surface dings, or is it just the contrary and the axial lighting method is meant to eliminate those effects?
I'm trying to "think through" the best set-up to construct, to use with my 35 mm extension-tube set..

[Roller]

Here is my set-up. I am prone to use what I have around the shop and house to make things work, especially when I'm experimenting. The stand is from an enlarging outfit and very solid that I have been using for some time. (You can pick up an enlarging outfit for next to nothing these days.) The lights are track lights (rewired) that I bought some time past for lighting for coin photography and abandoned because they did no work well in the original (not axial) set up. They work great for this axial set-up. They're attached to two lap joint framing pieces that you can pick up for a buck or two at any hardware store. The loose ends tuck neatly under the enlarging stand and you can line them up as you like. The light is more than adequate. 1/2 second shutter speed with 8 aperture works fine. The glass is attached to a block of wood (in this case I had a piece of walnut hanging around and wanting to be used for something) hinge screwed to the wood glued to the glass with Goop. Wood covered with black cloth. I cannibalized a protractor for the banana slip slot (or whatever that's called) with the appropriate hardware so that I could adjust the glass angle as I needed. I block the direct light to the coin with a piece of right angle (corner) trim material. Hope I did not bore you to tears. LOL

[Roller]

Meant to write "butt" not "lap" joint. If that makes any difference here. LOL. Need to go back to the woodshop soon.

[ray_parkhurst]

Only issue I see with your setup is that you are not blocking the light that reflects off the wall and then back to the glass, and up to the lens. The adjustable angle might help with this but even then it is very helpful for increasing contrast.

[styxman]

Roller – what a beast of a copy stand. That thing must be earthquake proof! I agree with Ray in that reflections off the white wall might give you some glare. A piece of cardboard with some black cloth draped over it set against the wall would eliminate any reflections. The slotted hinge guide is a nice touch in addition to the glued hinge. What type of bulbs is in the track lights? I see the Jansjo Desk Lamps tucked in the back – something I use all the time for direct lighting. My Jansjo lights are covered with ping-pong balls cut in half to help diffuse the light. Your lens system looks complicated – Nikon body attached to bellows attached to what looks like a 100mm lens attached to a zoom lens with a lens hood. Not sure how this works; I may be totally off base with what I see. What a great set up!

Silver1985, you pose some very interesting questions! To my understanding, Cartwheel luster is seen by slightly rolling a coin while reflecting a bright light off its surface. For me, the coin seems to rest at a 90 degree angle between the light source and my eye when seeing the “spokes” – see diagram Cartwheel_Luster.jpg. I looked through some coins to see if I could find a cartwheel spoke to photograph. I found that the coin should be positioned at a 45 degree angle to the lens as well as to the light source – see diagram. I believe I was able to capture a spoke (kinda) as shown in the 1964D Kennedy Half Dollar in the attached photos. The photo was made with the coin positioned at the 45 degrees between the coin surface and the camera lens (see Setup_Cartwheel_Luster). It required a stack of 140 shots with a step thickness of 0.200 mm (step = 200). I am not sure if you were asking how to shoot Cartwheel luster, but decided to give it a try. There is probably a better way, but this worked OK.

As for surface defects, I have found that the axial lighting seems to highlight them. I have uploaded a photo (Lighting_Compare_01) showing the same cent photographed with axial lighting and with direct lighting. The direct lighting was accomplished using 4 Jansjo Lamps (covered with a half of a ping-pong ball), all angled about 30 degrees down towards the cent, arranged 90 degrees apart with a distance of 2 cm from front of light to the coin. I tried to get the color/temperature to be about the same but failed miserably. My axial lighting setup is shown in photos Setup01 and Setup02 – a setup very similar to Rollers. I am not sure if you are trying to show surface defects or trying to hide them.

Through Rollers presentation, I believe he was trying to say that he prefers a setup which includes a vertical stand holding a camera pointed down towards the floor or table top, with the subject (coin) and lighting both being adjustable on the floor or a table top below the camera. I would have to agree with him. This configuration yields a very versatile setting for lighting, coin presentation, lens selection, and exposure control. I have used regular lenses, macro lenses, microscope objectives, enlarger lenses, bellows, extension tubes, and large format lenses. Additionally, I have used this system for single, stacked, multiple exposure, time lapse, long exposure, and stop motion photography. One disadvantage of the system is cost – a new very stable copy stand like those made by Kaiser have a price range from $500.00 to $20,000.00. A StackShot system costs from $600.00 to $1,500.00. Most of the items necessary to build this type of system can be found on ebay and many can be self-constructed as a means of controlling cost.

Others systems work just a well – like having your subject and camera on the same surface. Hopefully other forum members might be willing to share their photographic systems for comparison. I am continually amazed at the incredible quality of photographs displayed at LCR which were taken with phone cameras or other simple schemes. They put me to shame!

Not sure if any of this is helpful. Please let me know if there is something I missed or something that needs further illumination.

Over and out, styxman

[styxman]

ROR works great! Thanks so much for the lead!

[jfines69]

I like the detail the axial lighting shows!!!

[Roller]

Took care of the white wall; painted it black (just kidding). The track light bulbs are 50W GU 10 Shielded (UV filter 001 lenses). The camera setup is a D5100 Nikon on bellows with a Vivitar 90-180 Flat Field Zoom lens, no hood.

[silver1985]

http://www.lincolncentforum.com/forum/images/styles/Luburox_Blue/attach/jpg.gif Setup_Cartwheel_Luster.jpg (http://www.lincolncentforum.com/forum/attachment.php?attachmentid=109758&d=1461825720) (104.2 KB, 6 views)

[silver1985]

Your setup for cartwheel luster is interesting, in that it resulted in an image of the coin that was elliptical in shape. The best method to photograph cartwheel luster is to position the coin so that it is parallel to the camera lens (thus, a round image of the coin) and use a light source that is positioned at various angles (preferably a vertical fluorescent tube) and/or having parallel rays of light (preferably from the sun) or light source that is not a point source of light.

The image of the "compare" coins was very helpful and made the effects of axial lighting very apparent. To me, axial lighting highlights all the surfaces that are parallel to the camera lens and gives the rest of the coin surface various degrees of a shadowing effect. A very useful tool.

My interest is in producing the best image of the coin that would present the true condition of the coin for best appraisal by photograph. Mission impossible?
It's hard for me to experiment because all my good equipment is 35 mm film based, and therefore it's expensive to experiment.

[willbrooks]

no hood.

No wonder I am lost. Can't even find that half the time.

[silver1985]

The effects of axial lighting using the 1951-D was very interesting.

If you have an example of an extremely shiny Lincoln (i.e., 2016 Lincoln), it would broaden my evaluation.

Thanks

[Roller]

The effects of axial lighting using the 1951-D was very interesting.

If you have an example of an extremely shiny Lincoln (i.e., 2016 Lincoln), it would broaden my evaluation.

Thanks
I'm not into photography as a hobby and I don't much care about magazine quality, though I enjoy looking at it and thank those who spend the time to perfect this part of the hobby. Here is my shot (off the cuff) of a very bright 2015 WDO 014. As long as I get my message across with my shots, I'm satisfied. Normally, without the axial lighting, most of the detail in this shot would be obscured by glare in my experience. Some of the pros here don't use axial at all and get much better effects but they have been at it longer than I.

[silver1985]

I'm not into photography as a hobby and I don't much care about magazine quality, though I enjoy looking at it and thank those who spend the time to perfect this part of the hobby. Here is my shot (off the cuff) of a very bright 2015 WDO 014. As long as I get my message across with my shots, I'm satisfied. Normally, without the axial lighting, most of the detail in this shot would be obscured by glare in my experience. Some of the pros here don't use axial at all and get much better effects but they have been at it longer than I.

OK Thanks!

That's a real good picture and a good reference for the effects of axial lighting photography on coins with high mint luster.

[styxman]

It appears your track lights are halogen – running on 120V. If they will fit into the “up down” light fixture I am using, I will pick some up. I imagine they are fairly bright. I do not have my stand / camera setup on the floor; my back would not tolerate it. Instead my stand sits on an old rickety metal shelve that quakes with fear when walking close to it. As such, I still want a somewhat fast shutter speed and your lights might just be the ticket.

Thanks for the information about photographing Cartwheel Luster. I have not yet had the chance to hook up a long fluorescent tube but will try soon. You are right in that the coin appears elliptical as it was shot at a 45 degree angle giving it the oval shape. Next, I will take your advice and shot it flat with the long fluorescent tube.

I cannot image shooting FILM for these coin photos! Wow. I so remember the 35mm film with the bulk loaders, winding the film onto a real for developing and working the enlarger. Brings back very wonderful memories. I do believe you are correct with “Mission Impossible” as there is no one best way. I am still hopeful we can get other opinions on how to shot coins as the copier stand / axial lighting is just one of many ways to capture coins. I am sure it is not the best way when using a microscope objective with bellows. I have seen incredible images with the iPhone cameras, etc…..

I have uploaded some “Bright” shots of a 2016D cent and also included 1941 large and small S – something missing from the Die Varieties by Year (the links by WaterSport are all dead, labeled 1942 and need to be replaced). Will post duplicates in Die Varieties by Year. Jcuve has done an unbelievable job at supplying SUPER grade photos of most of the varieties for all the years. These pages are very useful when sorting through stock and guiding me in what to look for. Thank you jcuve and all who have contributed!

[styxman]

Roller, Is the Vivitar 90-180 Flat Field Zoom lens a macro / micro lens or do you get the magnification through the bellows?

[Roller]

Roller, Is the Vivitar 90-180 Flat Field Zoom lens a macro / micro lens or do you get the magnification through the bellows?
Its a macro made largely for dental photography back in the 36mm days. The bellows gives me additional magnification, something like a 1-1 ratio. The lens is heavy and somewhat costly.

[styxman]

Spent some time looking at reviews of your Vivitar lens. All were very impressive. There are some for sale on ebay - way out of my price range! You have a beast of a lens to go with your copy stand! Thanks for letting me know. Something to keep an eye out for....

[silver1985]

Was this pic (2016D Obv.jpg)


http://www.lincolncentforum.com/forum/images/styles/Luburox_Blue/attach/jpg.gif 2016D_Obv.jpg (http://www.lincolncentforum.com/forum/attachment.php?attachmentid=109902&d=1462010180) (220.9 KB, 2 views)

made with the axial lighting method?

[Roller]

No wonder I am lost. Can't even find that half the time.
Its hung right next to your robe.:sign10:

[willbrooks]

Its hung right next to your robe.:sign10:
I just always go for the bacon-looking thing. Never steers me wrong.

[silver1985]

My first attempt at axial lighting. Needs a lot of work. The coin has an iridescent sheen which can be clearly seen in the images. Please let me know what you think. I’ll continue to post photos as I improve the system.

Thanks much for all your comments and advice.

Over and out, styxman

I was wondering if you have used polarization filters in any of your lighting experiments, especially with the axial lighting setups and surface mint luster trials?

[Roller]

I was wondering if you have used polarization filters in any of your lighting experiments, especially with the axial lighting setups and surface mint luster trials?
My understanding is that polarizing filters do not work on reflections from solid objects like metals and with the angle of the glass shield there should not be any reflection to the lens from the glass anyway. So I don't see how a polarizing filter would help in this situation.

[silver1985]

My understanding is that polarizing filters do not work on reflections from solid objects like metals and with the angle of the glass shield there should not be any reflection to the lens from the glass anyway. So I don't see how a polarizing filter would help in this situation.

OK Thanks!

I've been diddleing around with photography for years and have never had a use for a polarization filter/lens, and therefore never bought one.
I was wondering if coin photography was the reason to own one.

[niknakphoto]

quick question on your set up. i am trying to get the set up right, and we are running into some complications.

just as a side note, this is for a museum, so we need museum quality images. the photo equipment we are using (not sure if this matters too much):
1) Hasselblad H5X
2) HC 120mm Macro Lens
3) PhaseIQ180 digital back
4) Broncolor Pulso G strobes

we are shooting below ISO 100, f/11 (i know it's still a bit wide of an aperture, but the IQ180 reads the sharpest at f/11), at 1/60. our strobes give us the ability to pump in more light if needed.

we have the axial setup almost there. we are using a wooden square frame (painted black), and are using black foam core to close off the sides. we are shooting on a gray background. i think where our problem lies is the glass. first off, it is casting a green color. secondly, no matter what we do, we can't get the coin in focus. I'm having a suspicion that our glass is just too think (1/4 in) however, i still dont understand how it can't give us sharp focus? could the light be refracting and distorting the image somehow? i read that buying a beamsplitter may work, and that the best results come from using glass that is 2mm thick. what kind of glass do you use?

[John D]

So far, the posts I read are by professional, caring people. This is a welcome relief from some other sites. I am looking forward to learning. John D

[jfines69]

Send a PM to ray_parkhurst... Also take a look at some of his postings... He is one of 2 (The other is JCuve) awesome coin photographers we have here... Ray sells equipment for coin photography... Here is a link to Rays website http://www.macrocoins.com/macrocoins.html

[ray_parkhurst]

quick question on your set up. i am trying to get the set up right, and we are running into some complications.

just as a side note, this is for a museum, so we need museum quality images. the photo equipment we are using (not sure if this matters too much):
1) Hasselblad H5X
2) HC 120mm Macro Lens
3) PhaseIQ180 digital back
4) Broncolor Pulso G strobes

we are shooting below ISO 100, f/11 (i know it's still a bit wide of an aperture, but the IQ180 reads the sharpest at f/11), at 1/60. our strobes give us the ability to pump in more light if needed.

we have the axial setup almost there. we are using a wooden square frame (painted black), and are using black foam core to close off the sides. we are shooting on a gray background. i think where our problem lies is the glass. first off, it is casting a green color. secondly, no matter what we do, we can't get the coin in focus. I'm having a suspicion that our glass is just too think (1/4 in) however, i still dont understand how it can't give us sharp focus? could the light be refracting and distorting the image somehow? i read that buying a beamsplitter may work, and that the best results come from using glass that is 2mm thick. what kind of glass do you use?

A thick beamsplitter will cause a fair amount of distortion, possibly enough to make the image never appear in proper focus. Even the relatively thin Edmund splitters cause this problem. This is one reason I have never been satisfied with an axial system.

When I do coin images that need axial content, such as deep toning or certain proofs, I will do what I call "pseudo-axial" lighting. I use a single large, diffuse light at 12:00, and place a mirror where the coin will be. I tilt the mirror until the center of the light shines directly into the lens. I use a goniometer for this, but just a manual tilt works fine. Prop the mirror up with something to hold the angle, then replace it with a disk or plate or something that will hold the coin and be its background. Place the coin and shoot.

Problems with this method are that focus may not be acceptable, and the coin will be distorted into a slight oval shape, due to the tilt. This can be fixed by using a tilt/shift adapter to compensate for the tilt optically. I use an adapter at the camera side that can tilt up to 8 degrees. They are fairly inexpensive. You can almost 100% compensate the coin tilt with camera tilt, and eliminate the perspective and distortion problems. The result is direct reflection off the coin similar to true axial lighting, but without the need for added glass in the optical path. Less glass means a more faithful image.

[styxman]

niknakphoto

Thank you for your questions. I have given your situation considerable thought and have a few ideas. Your list of photographic equipment sent me to the web to figure out what you are using. Wow – talk about being outside my league! An 80 Megapixel sensor is mind blowing – I hope you will share some of your photos when you are done.

The camera settings you describe sound just fine. An aperture of f/11 is sufficiently small to give you some good depth of field allowing for a good focus range (Hasselblad HC Macro 120mm f/4 II Lens). Additionally, a shutter speed of 1/60 of a second is short enough to avoid vibrations / shakiness issues. I cannot find any problems with these settings.

The inability to focus has me perplexed. My first thought relates to the foundation of your setup. Is your camera mount solid or does it shake if someone walks near your stand like mine does. I often get blurry images if I am moving about during the shot. Secondly, I wonder if your glass has some distortion as this would cause out of focus issues.

The green color, I suspect, comes from the iron oxide used as a lubricant in the manufacturing of glass. Please try a thin piece of glass as described by Ray Parkhurst on 02-07-2016 (Page 1) of this thread. At the suggestion of John (stoneman227), I have been using sheets of glass from Surplus Shed (http://www.surplusshed.com/). There are a couple of listings that might work: http://www.surplusshed.com/pages/item/m2115.html Plate glass, 5 inches by 5 inches by 0.08 inches thick. (10 plates for $4.50) and http://www.surplusshed.com/pages/item/l14674.html 88.3mm long by 61.5mm wide by 1.6mm thick. ($0.75). Both of these are classified as optical glass which should minimize the amount of iron oxide and assure that there are no defects or distortions within the glass.

Something to try in determining the cause of your focus problems is to take the camera, lens, and back outside and shot some non-macro photos. Make sure the focus problem lies in the bench / macro work and not a lens / camera / back mismatch. If the camera system works OK outside, then try just the camera with a close up of an object illuminated by a lamp or some simple light source – don’t use any glass between the object and the camera. One of these methods should help to isolate your focus problem.

As far as a beam splitter – I would listen to Ray’s comments as noted above. The only beam splitter I have used is with lasers – both argon and die. I am not sure if a beam splitter would work well with your Broncolor Pulso G Strobes.

You mention that you are using black foam core to close off the sides of your setup. Please make sure that you have something in front of your object to block the direct light from the strobe - see the attached diagram and photo. If the strobe light is flashing directly on the object, you will get ghost images, haziness, and a nonuniform lighting of the object. This could be the cause of your blurred images. In the attached photo, I have used a 6 inch black PVC pipe that has been cut to length and then split in half down the long axis. This prevents light from the source (strobe) from striking the object directly. Only the light reflected off the glass is used to illuminate the coin (object).

Hope something here will help. Please keep us posted and let us know if you are still having problems.

styxman

[niknakphoto]

niknakphoto

Thank you for your questions. I have given your situation considerable thought and have a few ideas. Your list of photographic equipment sent me to the web to figure out what you are using. Wow – talk about being outside my league! An 80 Megapixel sensor is mind blowing – I hope you will share some of your photos when you are done.

The camera settings you describe sound just fine. An aperture of f/11 is sufficiently small to give you some good depth of field allowing for a good focus range (Hasselblad HC Macro 120mm f/4 II Lens). Additionally, a shutter speed of 1/60 of a second is short enough to avoid vibrations / shakiness issues. I cannot find any problems with these settings.

The inability to focus has me perplexed. My first thought relates to the foundation of your setup. Is your camera mount solid or does it shake if someone walks near your stand like mine does. I often get blurry images if I am moving about during the shot. Secondly, I wonder if your glass has some distortion as this would cause out of focus issues.

The green color, I suspect, comes from the iron oxide used as a lubricant in the manufacturing of glass. Please try a thin piece of glass as described by Ray Parkhurst on 02-07-2016 (Page 1) of this thread. At the suggestion of John (stoneman227), I have been using sheets of glass from Surplus Shed (http://www.surplusshed.com/). There are a couple of listings that might work: http://www.surplusshed.com/pages/item/m2115.html Plate glass, 5 inches by 5 inches by 0.08 inches thick. (10 plates for $4.50) and http://www.surplusshed.com/pages/item/l14674.html 88.3mm long by 61.5mm wide by 1.6mm thick. ($0.75). Both of these are classified as optical glass which should minimize the amount of iron oxide and assure that there are no defects or distortions within the glass.

Something to try in determining the cause of your focus problems is to take the camera, lens, and back outside and shot some non-macro photos. Make sure the focus problem lies in the bench / macro work and not a lens / camera / back mismatch. If the camera system works OK outside, then try just the camera with a close up of an object illuminated by a lamp or some simple light source – don’t use any glass between the object and the camera. One of these methods should help to isolate your focus problem.

As far as a beam splitter – I would listen to Ray’s comments as noted above. The only beam splitter I have used is with lasers – both argon and die. I am not sure if a beam splitter would work well with your Broncolor Pulso G Strobes.

You mention that you are using black foam core to close off the sides of your setup. Please make sure that you have something in front of your object to block the direct light from the strobe - see the attached diagram and photo. If the strobe light is flashing directly on the object, you will get ghost images, haziness, and a nonuniform lighting of the object. This could be the cause of your blurred images. In the attached photo, I have used a 6 inch black PVC pipe that has been cut to length and then split in half down the long axis. This prevents light from the source (strobe) from striking the object directly. Only the light reflected off the glass is used to illuminate the coin (object).

Hope something here will help. Please keep us posted and let us know if you are still having problems.

styxman

Thank you for all the great information and tips! i would love to share the photos, but unfortunately I can't because it is for work and i cannot leak images from the museum. if they are posted up for publication, i will certainly share a link.

we have tested the focus with and without glass, and it is most definitely our glass that is causing the lack of focus; our lens focuses perfectly without it, so we are positive it is our glass that is the culprit. right now we are using regular frame glass, which more than likely has flaws and distortions within. My supervisor is trying to source a piece of glass at the moment, so thank you so much for your recommendations for optical glass. we were wondering if the relationship between the object and how close it is to the glass would affect the focus? or is it purely the quality of the glass that is giving us issues?
we are also working on a axial set in which we can set the glass at a desired angle more easily, and will be bolted down to a more solid surface. we do have a piece of foam core blocking direct light, but i wonder if it's not positioned correctly and some direct light is still spilling onto the object? tomorrow i will be testing if the foam core blocking direct light from the coin is contributing to the focus issue and i will report back.

@ray_parkhurt: Thanks for your reply!! i thought that i replied back but i guess i didn't submit it.
we are still doing testing with the glass, but i will definitely give your method a try and report back!

[ray_parkhurst]

The 1.6mm thick glass window that styxman links to above has a lot of potential. Even thinner would be better but 1.6mm is fairly thin. Definitely worth a try. I plan to buy several myself to test them out.

[styxman]

niknakphoto,

What a relief to hear that the glass is the culprit for your focus problems. Now that you have this solved, the rest is easy. Sorry about asking you to post your photos – my bad for not thinking about proprietary rights of the museum. What an exciting job you have!

The placement of the optical glass is crucial to getting the light just right. The distance between the object and the glass as well as between the glass and the camera lens makes no difference – as long as the edges of the glass do not come into play.

I use a Fisso articulating arm to position the optical glass. The one I use came from Amazon - https://www.amazon.com/Strato-3D-Line-Gaging-Arm/dp/B001C1B7AI/ref=sr_1_1?ie=UTF8&qid=1467273067&sr=8-1&keywords=fisso

The arm costs a lot - $245.00 and it is worth the price. To release the arm, simply loosen the one knob on the arm. Once loose, you can move it up, down, forward, backwards, right, left, rotate counter clockwise, rotate clockwise, angle up, angle down – any way you want. Once you have the glass properly positioned simply tighten the knob. The arm stays exactly where you positioned it – there is zero movement after the knob is snugged up. I mean zero. Additionally, the clamp that is supplied with the arm is perfect for holding a thin piece of glass. The base is small but heavy with retractable magnets. It is sound enough to hold the glass without the magnets, but if you can engage them then you could probably hold over 5 pounds. Please see attached photos. The blue tape is just to protect fingers from sharp, rough edges.

You might need a good light source to adjust the position of the optical glass as opposed to firing off the strobes a whole bunch of times. A museum should have a bunch of old 35mm slide projectors lying around somewhere. These make excellent continuous light sources for axial lighting. You will need to align the slide projector beam along the same axis as your strobe lights. Having a steady beam will allow you to get the angle of the glass just right so your strobe light will work as desired.

A last thought for the night: you might consider focus stacking if your coins are blurry on the top (or bottom) with the bottom (or top) sharp. This is indicative of a narrow depth of field where you can get only part of the coin in focus. Focus stacking can eliminate this problem should it arise. Let us know if you encounter this problem, we can walk you through the focus stacking technique.

Please keep us posted. It is always enjoyable to tackle these problems. It sounds as if you near to having an ideal setup.

Over and out, styxman

[niknakphoto]

thanks for the quick reply! and dont be sorry at all! i'm sorry that i cannot share full res images at this time.

we believe that our angle is correct, and seeing as the shape and sizes of the coins vary, we have our prep team constructing a setup in which we can adjust the angle accordingly. until that is finished we are just propping the glass at the angle in which the light looks best on the object. we do use a continuous light source to see what kind of light quality is on the object; the Pulso Gs have a great modeling light that you can adjust to show an approximate preview of what the object will look like when the strobes go off. We are using Helicon focus for focus stacking.

i tested the foam core that was blocking the light source, and although it did look better than what i was getting yesterday, focus is still not tack sharp. this leads me to believe that it IS our glass that is causing the problem. at 100%, details in the photo look streaky. i attached a detail at 100% with and without glass (both after focus stacking); the one of the left is with glass, and the one on the right is without. you can see a significant change in detail quality. for the pic on the left, we know that the little starbursts are due to helicon, but we have no idea why helicon is doing that; we are suspecting it is due to the issue with focus and that as soon as we achieve focus it'll stack much clearer.


http://www.lincolncentforum.com/forum/attachment.php?attachmentid=111715&stc=1

[jfines69]

I had the star bursts, using Helicon Focus, and realized the mounting for my camera was not 100% secure, had a minute vibration... Tightened it up completely, there was no further movement and the star bursts went away... If the glass you are shooting thru has any movement at all then that may be causing your problem... Hope that helps some!!!

[styxman]

niknakphoto

Excuse me while I extract my foot out of my mouth. It is absolutely wonderful to have another person running focus stacks. I believe there are several others using focus stacking: jcuve (Jason) who has tons of outstanding photos throughout the forum, notably in Die Varieties by Year. He has so many photos of varieties that he must own millions of coins. Someday I want to grow up and be like him! Ray Parkhurst: ray_parkhurst is the modern day Rembrandt of coin photography. You already know him; his web site is http://www.macrocoins.com/ . He has so many cool items it is hard to even begin to try to detail his work. The following internal link describes some of his work – just fantastic! http://www.lincolncentforum.com/forum/showthread.php?37965-Thanks-to-Ray-Parkhurst-he-solved-a-problem-with-his-fantastic-Photography&highlight=parkhurst .

Stoneman227 (John) has tons of absolutely outstanding examples in this forum, and is very knowledgeable. He is another individual I admire so much! There are others whose work is outstanding – I am a complete rookie in comparison to all of them. What I am trying to explain is that you have found a great site to get answers to your coin photography questions. These are really knowledgeable and kind folk who have helped me more than I can say.

Your uploaded images are excellent with incredible detail on the right image. As John has mentioned, the stars are most likely from a small wobble in your camera mount; I also get streaks from highly reflective areas if my camera is loose or if there is an angle between the object and the camera lens. I hope that once you get a good piece of optical glass and, tighten your camera, the detail found in the right image will be present in all your shots.

I believe Helicon Focus is the best Focus Stacking software as it allows for processing of camera raw images ( Hasselblad proprietary .3fr and .fff formats) . While Zerene Stacker is a bit faster, it only processes JPEG files. Not much more that I can add.

Your work is excellent and I hope we will get to see some of it when it is published. Please keep us posted on your progress.

Over and out, styxman

[ray_parkhurst]

I expect those stars are due to coma or other geometric aberrations of the axial lighting glass.

Your shot on the left is about as good as I've ever been able to achieve at 100% using tilted-glass lighting. I have done a bit better using both prisms and purpose-made axial lighting fixtures from microscopes. The one made by B&L in the 1960's has very thin glass (perhaps 0.5mm or maybe thinner) with good coatings, and does very well. I also have one made by Nikon, but have not yet tried it. Glass is similarly thin. The B&L still adds some distortion, and I expect the Nikon will as well.

I've heard rumors that Pellicle Beamsplitters eliminate this problem, but are difficult to use due to their extreme thin-ness. I have never taken the plunge.

None of the microscope or pellicle splitters will give you much flexibility in adusting lighting angles to bring in non-axial content like the tilted glass does. If you did adopt any of these, you would need to add non-axial fill lighting.

In the microscope world, both short working distances and the desire to eliminate these aberrations result in the use of coaxial splitters BETWEEN the objective lens and the ocular or camera. This is a better place for the splitter to be placed, and results in fewer aberrations. But again, the result is "pure axial", and would need additional non-axial content added to achieve the result you're looking for.

[niknakphoto]

niknakphoto

Excuse me while I extract my foot out of my mouth. It is absolutely wonderful to have another person running focus stacks. I believe there are several others using focus stacking: jcuve (Jason) who has tons of outstanding photos throughout the forum, notably in Die Varieties by Year. He has so many photos of varieties that he must own millions of coins. Someday I want to grow up and be like him! Ray Parkhurst: ray_parkhurst is the modern day Rembrandt of coin photography. You already know him; his web site is http://www.macrocoins.com/ . He has so many cool items it is hard to even begin to try to detail his work. The following internal link describes some of his work – just fantastic! http://www.lincolncentforum.com/forum/showthread.php?37965-Thanks-to-Ray-Parkhurst-he-solved-a-problem-with-his-fantastic-Photography&highlight=parkhurst .

Stoneman227 (John) has tons of absolutely outstanding examples in this forum, and is very knowledgeable. He is another individual I admire so much! There are others whose work is outstanding – I am a complete rookie in comparison to all of them. What I am trying to explain is that you have found a great site to get answers to your coin photography questions. These are really knowledgeable and kind folk who have helped me more than I can say.

Your uploaded images are excellent with incredible detail on the right image. As John has mentioned, the stars are most likely from a small wobble in your camera mount; I also get streaks from highly reflective areas if my camera is loose or if there is an angle between the object and the camera lens. I hope that once you get a good piece of optical glass and, tighten your camera, the detail found in the right image will be present in all your shots.

I believe Helicon Focus is the best Focus Stacking software as it allows for processing of camera raw images ( Hasselblad proprietary .3fr and .fff formats) . While Zerene Stacker is a bit faster, it only processes JPEG files. Not much more that I can add.

Your work is excellent and I hope we will get to see some of it when it is published. Please keep us posted on your progress.

Over and out, styxman

thanks so much for all your information! it's been extremely helpful to our research to get the lighting and focus just right.

we have contacted a company that makes optical glass and got a bunch of great information from them. they are sending us three free 6x6 beamsplitters (1mm, 2mm, 3mm) to test before we make a decision, so hopefully this will yield good results. if i find that this glass works better than what i've been getting, i will be sure to post the company, type of glass and the thickness as reference.

@ray_parkhurst the 1mm glass we are getting to test will be interesting to work with. the thinnest glass i've used is 1.5mm, so it'll be interesting to see what kind of results i get from it. while i what for the glass to come in, i may try the approach you suggested earlier without the glass.

i have also contacted the imaging science head at RIT and he DID bring up the pellicle beamsplitter. unfortunately we have been told that this glass is very pricey, but we will call up the company he directed us to and get a couple quotes.

[silver1985]

I've been following the discussion on this topic and was wondering if the digital camera being used has a "manual focus" option, and was used to "force" the correct focus on the object, has been considered in your experimentations.

[silver1985]

thanks for the quick reply! and dont be sorry at all! i'm sorry that i cannot share full res images at this time.

........... we are suspecting it is due to the issue with focus and that as soon as we achieve focus it'll stack much clearer.


http://www.lincolncentforum.com/forum/attachment.php?attachmentid=111715&stc=1

If your camera has a manual focus option, I am interested in knowing the results of the following test to correct the focusing confusion to the camera's autofocus, caused by the glass plate being in the depth of field for the aperture setting being used.

Set the focus option on the camera to MANUAL; remove the glass plate; focus the object (coin?) manually; place the glass plate in proper placement; set the f-stop as high as can be allowed for the lighting source being used; take the shot of the image. Compare images!

Thanks!

[ray_parkhurst]

For sure the camera will need to be slightly re-focused when the beamsplitter glass is put in place versus no glass, since it's in the optical path. Are you trying to figure out the amount of focus shift due to the glass?

[niknakphoto]

If your camera has a manual focus option, I am interested in knowing the results of the following test to correct the focusing confusion to the camera's autofocus, caused by the glass plate being in the depth of field for the aperture setting being used.

Set the focus option on the camera to MANUAL; remove the glass plate; focus the object (coin?) manually; place the glass plate in proper placement; set the f-stop as high as can be allowed for the lighting source being used; take the shot of the image. Compare images!

Thanks!
Hi! thanks for the reply!

yes, we did consider that, as we were absolutely confounded at how much trouble we were having with focus. we did the steps above using manual and auto. unfortunately, as soon as we put the glass back in, it would be extremely unfocused again. no matter what we did, we weren't getting tack sharp focus. i'll look around for our test shots with and without the middle glass and i'll edit this post.

[niknakphoto]

I just wanted to let you know that we are trying the method without the glass that you suggested now. i'm happy to see our coin in tack sharp focus for once! :xd:

we have a test quarter on a frosted plexi, which is being lit from below with a pulso g bouncing light off a mirror, and another pulso g with a softbox from camera right coming from high up. our coin is tilted slightly toward the softbox.
we are shooting with our regular 120mm macro at the moment, as we are on the search for our linhof sliding back so we can get the linhof 4x5 up and running and fix distortion in camera, but from what i can see, it is lighting the coin nice and evenly. so we will see what the ancients look like once we get the setup right.

[ray_parkhurst]

I just wanted to let you know that we are trying the method without the glass that you suggested now. i'm happy to see our coin in tack sharp focus for once! :xd:

we have a test quarter on a frosted plexi, which is being lit from below with a pulso g bouncing light off a mirror, and another pulso g with a softbox from camera right coming from high up. our coin is tilted slightly toward the softbox.
we are shooting with our regular 120mm macro at the moment, as we are on the search for our linhof sliding back so we can get the linhof 4x5 up and running and fix distortion in camera, but from what i can see, it is lighting the coin nice and evenly. so we will see what the ancients look like once we get the setup right.

Sounds good!

If you will have camera standard movements available, you can use either tilt or shift to compensate the offset. Tilt is easiest, but shift can compensate both distortion AND perspective. I would suggest trying both to see the best result with the Ancient coins.

[niknakphoto]

Sounds good!

If you will have camera standard movements available, you can use either tilt or shift to compensate the offset. Tilt is easiest, but shift can compensate both distortion AND perspective. I would suggest trying both to see the best result with the Ancient coins.

so we shot an ancient on the set, and it came out pretty well! only thing is we have to wait for out linhof digital back plate to come back from repairs before we can really start fixing distortion in camera. one thing we are a bit concerned with is the fact that we do not have a great mount to tilt the coin; we also would have to touch the coins constantly in order to get the right angle towards the softbox, as all our coins are different shapes and textures. conservation does not really want us to excessively handle the coins, so if we take this route, we will have to come up with something easy and constant where we won't need to touch the coin often. we are now going to test a smaller light source for this set (changing from a small softball to a pico box).

we also got the three sheets of glass in. the 1mm optical glass from PGO worked like a charm! getting tack sharp focus! now our decision of which set to shoot these coins on comes down to our head curator and see what he prefers.

a question i have is, is there a way to shoot on the axial set with the coin on a gray background? my manager wants to see results of it, since it would help our imaging techs during post production; we have about 4000 ancients to shoot and shooting on gray would cut one extra step in the process. however i am not confident that it will work; it would definitely reflect off the glass and fog the image correct?

[niknakphoto]

so here are my findings with using different glass thickness on the axial setup.
we got three free 6x6" optical glass plates from PGO to test, all varying in thickness. these details of the three shots were shot with the same lighting and same set up, just different glass. we focus stacked with helicon.
the 1mm thickness is without a doubt the best choice.

going from left to right: 2mm, 3mm, 1mm


http://www.lincolncentforum.com/forum/attachment.php?attachmentid=111879&stc=1

[styxman]

Well, that's a slam dunk! I would have never guessed that 1 mm thickness of glass would make that much difference. I am very impressed with your work and the knowledge of Ray Parkhrust! Hand me that box of cover slips. I shot all my coins on a flat surface with an optical gray paper as background. If you are getting a lot of assistance with back-illumination, then covering your back light source with gray paper makes little sense. If you can achieve a good lighting with just the beam splitter and strobes, then using the gray background would probably be OK. With a flat surface, a positioning apparatus should be fairly elementary. (My Mon used to be a curator at the Denver Museum of Natural Science – many many years ago, and I still remember hearing her yell – “Put your gloves on.” I am very respectful of all curators and have suffered their wrath more than once. Keep your head low.) If you find that an angle between the lens and the coin is best, one might consider angling the camera – leaving the coin flat. Then, as Ray has mentioned, adjustment with standard movements might yield the correct alignment. Just some thoughts.

[ray_parkhurst]

It looks like the 1mm has pretty low distortion, perhaps less than can be captured by the sensor. I'd be very interested to get similar 6"x6" 1mm optical glass plates to try (yet again) to see if I can be satisfied with an axial setup. Would you mind providing the sourcing info? I'm hoping the plates are not too expensive...

[niknakphoto]

Well, that's a slam dunk! I would have never guessed that 1 mm thickness of glass would make that much difference. I am very impressed with your work and the knowledge of Ray Parkhrust! Hand me that box of cover slips. I shot all my coins on a flat surface with an optical gray paper as background. If you are getting a lot of assistance with back-illumination, then covering your back light source with gray paper makes little sense. If you can achieve a good lighting with just the beam splitter and strobes, then using the gray background would probably be OK. With a flat surface, a positioning apparatus should be fairly elementary. (My Mon used to be a curator at the Denver Museum of Natural Science – many many years ago, and I still remember hearing her yell – “Put your gloves on.” I am very respectful of all curators and have suffered their wrath more than once. Keep your head low.) If you find that an angle between the lens and the coin is best, one might consider angling the camera – leaving the coin flat. Then, as Ray has mentioned, adjustment with standard movements might yield the correct alignment. Just some thoughts.

we definitely all use gloves in the studio. we have a mandatory weeklong training on conservation alone. :)

the reason i ask about the gray background is purely to help our technicians edit these images quicker. we have another 4000 of these coming in and we just need a system in which we can shoot many coins in one day. i just tried a regular quarter on gray and it looks okay, but i'm definitely gonna keep working on it and i need to see what the actual coin looks like on set. right now the background is a little up in the air, because we are awaiting curator approval on what standard he wants to go with, so there are a lot of outside factors that are determining how we shoot these, but i figured i'd explore every avenue so that he can make an informed decision. as far as our other set without the glass, we need to wait for our linhof plate to come back from repairs so that we can actually fix distortion in camera.

@ray parkhurst: the site we got it from is http://www.pgo.com
we told the customer service rep that we were testing and he was nice enough to ship over three free plates. I'm not 100% sure of the cost since my manager was the one who called them. it may very well be quite pricey. :(

[jfines69]

I like to use a flat black back ground... For me it is a better contrast from the coins!!!

[ray_parkhurst]

@ray parkhurst: the site we got it from is http://www.pgo.com
we told the customer service rep that we were testing and he was nice enough to ship over three free plates. I'm not 100% sure of the cost since my manager was the one who called them. it may very well be quite pricey. :(

Thanks, I have contacted them, am waiting for reply.

I see they have "official" beamsplitter glass at 1.6mm thickness.

[styxman]

Just contacted PGO. They have a beamsplitter with a 50/50 transmission/reflection ratio that is 1mm thick. I have requested a quote and will let you know the cost when they return my email.

[styxman]

Received the quote from PGO showing that a 5 inch by 5 inch 50/50 1mm thick beamsplitter is $98.00. Rather pricey, but I am not sure if there is any alternative.

[silver1985]

Well, that's a slam dunk! I would have never guessed that 1 mm thickness of glass would make that much difference.

I would be interested in comments from those who use cameras with 20 MegPixel sensors for coin photography. The conclusion that a 1 mm (+/-) glass plate produces satisfactorily "focused images" with the museums camera having an 80 MegPixel sensor, should imply that a glass plate that is 4 mm thick would produce the same focusing quality with a camera having a sensor with a 20 MegPixel rating.

[ray_parkhurst]

1985...this seems logical, but unfortunately the physics goes the other direction. Rather than the MP rating, it is the pixel pitch that is relevant in these considerations. The 80MP IQ180 has a Large Format (LF) sensor, with dimensions 53.9mm x 40.4mm. The sensor has 10,328 x 7760 pixels, such that the pixel pitch is about 5.2um. These are rather large pixels. Compare this with a 20MP Canon 70D. Its sensor is 22.5mm x 15mm, with 5472 x 3648 pixels, such that the pixel pitch is 4.1um. The smaller pixels of the 20MP sensor make most optical considerations more difficult. The 20MP camera will actually require a bit thinner glass to have similar performance to the 80MP camera.

[silver1985]

1985...this seems logical, but unfortunately the physics goes the other direction. Rather than the MP rating, it is the pixel pitch that is relevant in these considerations. The 80MP IQ180 has a Large Format (LF) sensor, with dimensions 53.9mm x 40.4mm. The sensor has 10,328 x 7760 pixels, such that the pixel pitch is about 5.2um. These are rather large pixels. Compare this with a 20MP Canon 70D. Its sensor is 22.5mm x 15mm, with 5472 x 3648 pixels, such that the pixel pitch is 4.1um. The smaller pixels of the 20MP sensor make most optical considerations more difficult. The 20MP camera will actually require a bit thinner glass to have similar performance to the 80MP camera.

That's fantastic information on the sensor dimensions. My calculations hit your conclusion right on the head!
Thanks for the info!
I calculate that the 20 MP sensor would require a piece of glass that is 0.7893 mm thick to record the same (focus) shift between the red and blue, RGB matrices as the 80 MP camera sensor would record using a 1 mm thick piece of glass in the direct axis lighting setup.
Sound close to you?
Coin Photography sure is an interesting hobby!

[silver1985]

That's fantastic information on the sensor dimensions. My calculations hit your conclusion right on the head!
Thanks for the info!
I calculate that the 20 MP sensor would require a piece of glass that is 0.7893 mm thick to record the same (focus) shift between the red and blue, RGB matrices as the 80 MP camera sensor would record using a 1 mm thick piece of glass in the direct axis lighting setup.
Sound close to you?
Coin Photography sure is an interesting hobby!


More RGB information for the Axial Lighting Photography Analysis!

[ray_parkhurst]

Good stuff 1985! Even more interesting is the sensor demosaicing. In the attachment you provided, each of the pixels has full RGB information. But in real life each pixel is only an R, G, or B, and the other colors must be interpolated from surrounding pixels in order to get full color information. What this really means is that your 20MP sensor is "really" only a 5MP sensor of full RGB info. Some demosaicing algos are better than others, but I have yet to see anything close to full resolution at 100% pixel level. Look here for more info:

https://en.wikipedia.org/wiki/Demosaicing

[silver1985]

Good stuff 1985! Even more interesting is the sensor demosaicing. In the attachment you provided, each of the pixels has full RGB information. But in real life each pixel is only an R, G, or B, and the other colors must be interpolated from surrounding pixels in order to get full color information. What this really means is that your 20MP sensor is "really" only a 5MP sensor of full RGB info. Some demosaicing algos are better than others, but I have yet to see anything close to full resolution at 100% pixel level. Look here for more info:

https://en.wikipedia.org/wiki/Demosaicing


Interesting! Makes my pixels spin!

I wastrying to determine if there was an association between the principle ofrefraction in the glass and the problem the museum personnel was having withfocusing, with the high-end Hasselblad camera. Do you see any information inthe referenced Wikipedia article that indicates that refraction is messing withthe auto-focus (vertical and/or horizontal) contrasting technology?
Iwondering if this high-end camera would be able to properly focus on an objectthrough a regular glass window, if it was held at a 45 degree angle with theglass in the window.

[ray_parkhurst]

If the glass had a perfectly consistent thickness, and a refraction index that was constant across all RGB, then (I don't think) it wouldn't matter how thick it was, it would not cause blurring. Thicker glass would just cause a larger lateral "shift" to the image due to the non-zero refraction index. The problem is that refraction index is not constant vs wavelength, nor is the thickness of the glass. Because of this, color information that should be sensed by a pixel has information that is spread from other pixels, causing a blur. The "optical glass" that was sourced by PGO has better-controlled thickness and (likely low) refraction index, so has less effect than simple plate glass. Still, thinner is better because a single glass type cannot transmit all colors equally.

[styxman]

Additionally, a thinner sheet of glass would have few "pockets" of altered index of refraction within the glass than a thick sheet of glass.

[Scott]

Very interesting .