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 Replies: 19 / Views: 3,989 |
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Pillar of the Community
United States
4038 Posts |
A long while back I introduced the concept of calibrating a studio photomacrographic system for planarity between lens and subject using a mirror. The concept is to place a mirror on the surface the coin will sit on, set the lens aperture to f/22 or smaller, and then adjust the camera X/Y tilt so that you can see the center of the lens in the center of the image. This guarantees the best sharpness across the whole coin at any aperture setting. Recently, I have discovered the perfect mirror for this application. The Darice company makes mirrors for craft use in various sizes and shapes. You can purchase them at all the craft stores (JoAnns, Michaels, etc). I recommend the 3" diameter ones as they are big enough for the intended purpose but still easy to handle and store. They come 2 in a pack for <$4. The reason I choose these particular mirrors is they are painted on their backside with a light grey finish that is useful as a background for coin shooting. It's not quite a perfect grey (it's about -7% red, +7% blue) but that is easy to compensate for during white balancing. Here is a link to the mirrors on Amazon: http://www.amazon.com/Darice-1613-4...+mirror+3%22 |
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Pillar of the Community
United States
4132 Posts |
These are the exact mirrors I use (from Michaels even).
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Pillar of the Community
United States
627 Posts |
I was trying to explain this to someone a while back, and to do so created this schematic. I found it helpful to go along with the verbal description. Thanks for the link Ray. As always, you are THE guru...and your help along the way is the only reason why I am a competent numismatic photographer today! ![[tip-#1]--Multi-Purpose-Mirrors](http://i1202.photobucket.com/albums/bb364/brg5658/Photo_HowTo/Centering_the_viewfinder_zpsedabc3fb.jpg) |
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Pillar of the Community
 United States
4038 Posts |
Excellent graphic explanation Brandon! Much better than verbal...Ray
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Moderator
United States
23522 Posts |
Wonderful graphic, brg. May I use it in the future as an educational tool?
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Pillar of the Community
United States
627 Posts |
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Wonderful graphic, brg. May I use it in the future as an educational tool? Most certainly. Use it for any purpose you may need. |
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Pillar of the Community
United States
3546 Posts |
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...guarantees the best sharpness across the whole coin at any aperture setting I am still unclear comprehending the logic of how the mirror/reflectivity functions to allow the camera to capture optimum sharpness. I do understand, however, that even a larger coin such as a Peace would still have portions of the mirror beneath the coin reflecting light back up to the lens' aperture but to a lesser extent compared to a Roosy, for example. In summary I guess the inquiries would be: 1) what exact properties of either the lens and/or the mirror combine so as to 'alter' the light towards enhanced/uniform clarity and 2) assuming the diameter of the underlying mirror remains a constant what have been the most common & effective adjustments factoring in fluctuations in coin breadths and patina reflectivity? |
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Pillar of the Community
United States
4038 Posts |
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1) what exact properties of either the lens and/or the mirror combine so as to 'alter' the light towards enhanced/uniform clarity and The mirror technique guarantees the distance all around the edges of the coin are equal. Depth of field is pretty shallow when you are operating at large apertures required for best sharpness, so any difference in distance top/bottom or left/right can cause part(s) of the coin to go out of focus. Quote:
2) assuming the diameter of the underlying mirror remains a constant what have been the most common & effective adjustments factoring in fluctuations in coin breadths and patina reflectivity? Most important thing is the angle vs horizontal of the light source. For coins with deep toning patina, my preference is to bring the light up so that it is nearly axial but not quite. Some folks go for partial axial and partial non-axial. The lights need to be adjusted for each size coin to get the correct reflection angles. |
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Moderator
United States
23522 Posts |
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I do understand, however, that even a larger coin such as a Peace would still have portions of the mirror beneath the coin reflecting light back up to the lens' aperture but to a lesser extent compared to a Roosy, for example.
Um, you take the mirror away before shooting coins....this is a setup tool for positioning the camera. |
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Pillar of the Community
United States
4038 Posts |
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Um, you take the mirror away before shooting coins....this is a setup tool for positioning the camera. OK, that makes more sense now. Actually, with the Darice mirrors, you can flip the mirror over and use the other side as a grey background for shooting the coins! But indeed you don't want to have light reflecting from the mirror during the actual imaging. |
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Moderator
United States
23522 Posts |
I don't think we sufficiently emphasize the importance of keeping extraneous light away from the camera. The only light to hit the lens has to be that reflected from the coin. Anything else costs you contrast, and the improvement in contrast offered by high-quality imaging systems is at least as important as the extra sharpness. There shouldn't even be nearby walls capable of reflecting light, and that's why I recommend black over white or grey for a background. Grey is OK but I'm paranoid.  |
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Pillar of the Community
United States
4038 Posts |
Most recently I've been using a cone attachment to vignette all but the coin itself with a small amount around it. This eliminates possibility of extraneous light getting in. It also gives a perfect mount for my diffusers. I should post a pic, I know. Maybe it will be tip#2...
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Pillar of the Community
United States
3546 Posts |
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...recommend black over white or grey for a background I am in that same camp for the greater majority of my coins especially the silver ones having a proof-like or highly reflective surface. |
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Pillar of the Community
United States
3546 Posts |
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...cone attachment to vignette all but the coin itself A picture is worth a thousand words especially in my case since I could mistakenly ask what flavor of ice cream does your cone taste the best with.  I really would like to avoid asking a third dumb question since three is my self-imposed limit for these type of misdirected inquiries. |
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Moderator
United States
23522 Posts |
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I really would like to avoid asking a third dumb question since three is my self-imposed limit for these type of misdirected inquiries.
The only dumb question is the one unasked. Employ various measures to constrict the light falling upon the coin, the goal being to achieve a perfectly regular and circular pattern of light a little larger than the subject coin. No excess light, anywhere. It'd be cool if you could do that by concentrating the light into greater coherence, meaning less lumens lost, but that's a bit complex optically so rather than building a laser we choose to create specific shapes from varying diffuser papers to achieve the same. Losing extraneous light is that important. |
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Pillar of the Community
United States
1476 Posts |
Sorry to breath life back into this old thread but I am wondering if anyone was going to post pictures of the various setups mentioned here. Pictures of what devices/reflectors ect you are using to diffuse light as mentioned.
Oh, and did I miss Tip #2?
Edited by Dar
05/04/2015 5:08 pm
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Replies: 19 / Views: 3,989 |
Posted 03/07/2015 2:57 pm
