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Message:: [QUOTE="dougsmit, post: 1953325, member: 19463"]I'm sorry I missed this discussion when it was current but those interested will want to study up on the term 'diffraction' which will explain why coins do not get sharper when you stop down too far.  In general, a 1.6x crop camera should not be stopped down past f/8 and a full frame past f/11 unless you are willing to trade a little sharpness for the additional depth of field.  <a href="http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm" target="_blank" class="externalLink ProxyLink" data-proxy-href="http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm" rel="nofollow">http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm</a>When you need depth of field, try using a focus stacking program like the freeware CombineZ (there are ones you pay for if you like to waste money).   Finally, I can not believe anyone can keep a straight face talking about sharpness when shooting slabbed coins.  Even the cleanest plastic is a lot worse than air.  For that matter, don't use a filter to 'protect' your lens either.  Everything between lens and subject degrades sharpness.  Everything. The top parts below are reduced; the bottom 100% as shot but cropped to fit.  Canon 100mm macro.  I have very few US coins and no slabs.  [ATTACH=full]342798[/ATTACH] [ATTACH=full]342799[/ATTACH] [ATTACH=full]342800[/ATTACH] [ATTACH=full]342801[/ATTACH][/QUOTE]