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<p>[QUOTE="rmpsrpms, post: 4987293, member: 31773"]Backlights are a really bad idea for coins, where accurate color is desired. The only light you want hitting the lens is what is coming from the coin. Light from the backlight can cause problems 3 ways:</p><p><br /></p><p>1...it can enter the lens directly and change the colors through "lens flare", internal reflections within the lens, etc</p><p><br /></p><p>2...it can reflect off surfaces in the environment, shine onto the coin, and then up to the lens</p><p><br /></p><p>3...it can reflect off the lens itself, back to the coin, and then back up to the lens. </p><p><br /></p><p>All of these effects are subtle, but they can detrimentally change the color and contrast of the coin image. </p><p><br /></p><p>My recommendation is always to shoot on as black a background as you can. I use astrophotography-grade photographic velvet. It is very non-reflective, and provides a safe surface for the coin to sit on. The exposure can be adjusted to black out the background prior to the shot, or black level can be adjusted after the shot, depending on desired workflow. Only issue is that dust on the velvet will show up, so it must be kept clean and dust-free to minimize postprocessing work. </p><p><br /></p><p>In some of the photo systems I've built over the years I have used lenses with more than acceptable levels of flare. For these lenses an aggressive lens hood does the trick to eliminate the flare. I suppose a hood with a rectangular aperture might be suitable for use with a backlit system to minimize the total amount of light coming from the backlight. You would still need to ensure minimal reflections off of the environmental surfaces but the hood may give enough flare and reflection suppression to allow backlights to work. It might be worth a try for folks who really want to use a backlight but are bedeviled by the problems it causes.[/QUOTE]</p><p><br /></p>
[QUOTE="rmpsrpms, post: 4987293, member: 31773"]Backlights are a really bad idea for coins, where accurate color is desired. The only light you want hitting the lens is what is coming from the coin. Light from the backlight can cause problems 3 ways: 1...it can enter the lens directly and change the colors through "lens flare", internal reflections within the lens, etc 2...it can reflect off surfaces in the environment, shine onto the coin, and then up to the lens 3...it can reflect off the lens itself, back to the coin, and then back up to the lens. All of these effects are subtle, but they can detrimentally change the color and contrast of the coin image. My recommendation is always to shoot on as black a background as you can. I use astrophotography-grade photographic velvet. It is very non-reflective, and provides a safe surface for the coin to sit on. The exposure can be adjusted to black out the background prior to the shot, or black level can be adjusted after the shot, depending on desired workflow. Only issue is that dust on the velvet will show up, so it must be kept clean and dust-free to minimize postprocessing work. In some of the photo systems I've built over the years I have used lenses with more than acceptable levels of flare. For these lenses an aggressive lens hood does the trick to eliminate the flare. I suppose a hood with a rectangular aperture might be suitable for use with a backlit system to minimize the total amount of light coming from the backlight. You would still need to ensure minimal reflections off of the environmental surfaces but the hood may give enough flare and reflection suppression to allow backlights to work. It might be worth a try for folks who really want to use a backlight but are bedeviled by the problems it causes.[/QUOTE]
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