ray_parkhurst
09-23-2012, 08:34 AM
I have been thinking about "Diffraction Limited Aperture" (DLA)lately and effect on my imaging. DLA is dependent on the size of the pixels on the sensor. The smaller the pixels, the larger the aperture required to not have the image sharpness degraded by diffraction. For a few select Canon cameras, the DLAs are:
XS / 40D; 10.1MP; pixel size 5.7um; DLA = f9.1
XSi / T3; 12.2MP; pixel size 5.2um; DLA = f8.3
T1i / 50D; 15.1MP; pixel size 4.7um; DLA = f7.5
T2i / 60D; 18.0MP; pixel size 4.3um; DLA = f6.8
Any smaller (effective) aperture than the above and your shots will be limited by diffraction.
I got to thinking that because of the above, perhaps there would be little benefit for coin photography to having more and more pixels in the same sensor size. Larger sensors with more of the same size pixels gives a bigger field of view, but has other issues (such as lower effective magnification and of course $$) that make full-frame cameras less attractive for macro work. So what about going backward to earlier generations of cameras with same size sensors but fewer pixels, for effectively better DLA?
A problem is that if you have fewer pixels to work with, for same down-sizing ratio you will have smaller final image size. But is that such a big deal?
To test it all out, I got onto eBay and looked for a suitable guinea pig. I found a Rebel XS for sale for $109 (cheap!), body only (perfect, I don't need any more lenses), and with a minor problem with the flash card port (I don't use flash cards on bellows anyway). A few days later, my "new" XS arrived and I was doing comparison shots.
I only looked as far back as the XS and the 40D not because of sensor size, but because those are the first cameras in the Canon lineup that offer Live View, which is of course ultra-critical to have.
So I had not done the calculations before, but once I got the camera and started downsizing I discovered a nice mathematical property to the Canon sensors...going from XS at 10.1MP (3888 x 2592) to the T2i at 18MP (5184 x 3456) the ratio is a convenient 33% increase. This means that I can downsize the T2i images by 4x, and the ES images by 3x, and end up with the same 1292x864 final image size for web publishing. I usually crop whole coin images to 800x800 and either camera allows this while still maintaining an integer downsizing ratio, which I consider important for maintaining sharpness. I leave variety shots un-cropped.
So how's the result? Here are the two images, 5x variety shots of a Lincoln Cent RPM. I did this first since I wanted to prove the EFSC was functional on the ES. At 5x, with no EFSC the loss of sharpness would be very apparent.
Canon Rebel ES:
http://i943.photobucket.com/albums/ad273/rparkhurst/ES_1000D_zps7c4bfe86.jpg
Canon Rebel T2i
http://i943.photobucket.com/albums/ad273/rparkhurst/T2i_550D_zps4a613b26.jpg
My conclusion is that these are essentially equivalent in sharpness. The difference in DLA is offset by the sharpness improvement of 4x vs 3x downsizing. What this means to me is that I can recommend ANY of the recent Canon lineup shown above for coin photography. More pixels doesn't give a better result. I believe all that matters is the camera is new enough to have Live View and EFSC.
Would love to hear your thoughts on this...Ray
XS / 40D; 10.1MP; pixel size 5.7um; DLA = f9.1
XSi / T3; 12.2MP; pixel size 5.2um; DLA = f8.3
T1i / 50D; 15.1MP; pixel size 4.7um; DLA = f7.5
T2i / 60D; 18.0MP; pixel size 4.3um; DLA = f6.8
Any smaller (effective) aperture than the above and your shots will be limited by diffraction.
I got to thinking that because of the above, perhaps there would be little benefit for coin photography to having more and more pixels in the same sensor size. Larger sensors with more of the same size pixels gives a bigger field of view, but has other issues (such as lower effective magnification and of course $$) that make full-frame cameras less attractive for macro work. So what about going backward to earlier generations of cameras with same size sensors but fewer pixels, for effectively better DLA?
A problem is that if you have fewer pixels to work with, for same down-sizing ratio you will have smaller final image size. But is that such a big deal?
To test it all out, I got onto eBay and looked for a suitable guinea pig. I found a Rebel XS for sale for $109 (cheap!), body only (perfect, I don't need any more lenses), and with a minor problem with the flash card port (I don't use flash cards on bellows anyway). A few days later, my "new" XS arrived and I was doing comparison shots.
I only looked as far back as the XS and the 40D not because of sensor size, but because those are the first cameras in the Canon lineup that offer Live View, which is of course ultra-critical to have.
So I had not done the calculations before, but once I got the camera and started downsizing I discovered a nice mathematical property to the Canon sensors...going from XS at 10.1MP (3888 x 2592) to the T2i at 18MP (5184 x 3456) the ratio is a convenient 33% increase. This means that I can downsize the T2i images by 4x, and the ES images by 3x, and end up with the same 1292x864 final image size for web publishing. I usually crop whole coin images to 800x800 and either camera allows this while still maintaining an integer downsizing ratio, which I consider important for maintaining sharpness. I leave variety shots un-cropped.
So how's the result? Here are the two images, 5x variety shots of a Lincoln Cent RPM. I did this first since I wanted to prove the EFSC was functional on the ES. At 5x, with no EFSC the loss of sharpness would be very apparent.
Canon Rebel ES:
http://i943.photobucket.com/albums/ad273/rparkhurst/ES_1000D_zps7c4bfe86.jpg
Canon Rebel T2i
http://i943.photobucket.com/albums/ad273/rparkhurst/T2i_550D_zps4a613b26.jpg
My conclusion is that these are essentially equivalent in sharpness. The difference in DLA is offset by the sharpness improvement of 4x vs 3x downsizing. What this means to me is that I can recommend ANY of the recent Canon lineup shown above for coin photography. More pixels doesn't give a better result. I believe all that matters is the camera is new enough to have Live View and EFSC.
Would love to hear your thoughts on this...Ray