Question for Ray or anyone else in the know

[Roller]

Please ignore all the issues with this shot except the umbra/reflection of the east edge beyond the primary image. I chose this shot only because it clearly shows what I'm posting about. I am using axial lighting. The umbra shows much less on shots taken with tighter apertures (this one was taken with 8). 11 produces a very sharply detailed image but the anomaly still shows, though less visibly. My light source is a slide film projector and I have a black background behind the set up. I have taken some 50 shots with different apertures and exposure times; have moved the reflective glass to several positions to see if that was causing the problem (this shot it is set a 45 degrees to lens and light source); have moved the light source in various distances from the glass; etc, etc, and still can't get rid of the problem. Any suggestions as to what may be causing this? Thanks in advance.

[Petespockets55]

I have no experience with this type of lighting but what is the thickness of the glass the images are taken through? Was the glass closest to the coin where the umbra is?

Do you think it's possible it is a distorted image from the second side of the glass? Maybe a different or special type of glass might help?

[Jacob]

I think you have to put a white cover over the lighting to dull brightness of light.

[jfines69]

That is a tuff one and most likely Ray will need to see this... If this is occurring on all of your shots for different coins in the same spot I would think it may be an issue with the camera lens or sensor??? One other possibility would be an extraneous light source causing a ghost image to show???

[ray_parkhurst]

I have no experience with this type of lighting but what is the thickness of the glass the images are taken through? Was the glass closest to the coin where the umbra is?

Do you think it's possible it is a distorted image from the second side of the glass? Maybe a different or special type of glass might help?

Sorry for late reply, just seeing this. I do think the problem is a reflection off the glass. What are you using for a reflector?

[Petespockets55]

Sorry for late reply, just seeing this. I do think the problem is a reflection off the glass. What are you using for a reflector?

Thanks for the insight.
The reason I thought the glass might be the issue is because years ago some window manufacturers decided to put multiple layers(4?) of micro-thin and separated plastic in their insulated windows to increase the insulating ability. What I remember most about the experiment was the multiple images that were visible when looking at items at an angle. (Straight on everything seemed to be ok.)

[Roller]

Sorry for late reply, just seeing this. I do think the problem is a reflection off the glass. What are you using for a reflector?
Saw this reply just now. My original pane was broken so I just took one from a small picture frame.

[ray_parkhurst]

Picture frame glass has a couple issues that make it non-optimum. First, it's too thick. I have found that anything >1mm really causes problems for reflections and distortion. And second, it has no anti-reflective coatings. If you are serious about doing this type of lighting, you should get some "real" 50/50 glass with anti-reflective coatings.

I have a backburner project to build an axial lighting system using such "real" glass, and will publish the results here when I get around to it.

[Roller]

Picture frame glass has a couple issues that make it non-optimum. First, it's too thick. I have found that anything >1mm really causes problems for reflections and distortion. And second, it has no anti-reflective coatings. If you are serious about doing this type of lighting, you should get some "real" 50/50 glass with anti-reflective coatings.

I have a backburner project to build an axial lighting system using such "real" glass, and will publish the results here when I get around to it.
Thanks. I will see to getting it and will report back.

[Roller]

Thanks. I will see to getting it and will report back.

I had no idea how "serious" and "real" this item is. Was told that an 8" X 5" would cost some $50 and would need to be special ordered. Wow!

[ray_parkhurst]

I had no idea how "serious" and "real" this item is. Was told that an 8" X 5" would cost some $50 and would need to be special ordered. Wow!

There are a few eBay sellers that sell beamsplitter glass. You don't really need a big piece of it, and in fact a big part of my project is to figure out how to work with much smaller beamsplitters.