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<p>[QUOTE=&quot;dougsmit, post: 2608752, member: 19463&quot;]Diopter lenses come in +1 to +10 strengths with each number slightly more powerful than the one before.&nbsp; They degrade the image slightly if they are the expensive two element versions and a lot if they are one element versions that usually come in sets for very low prices. They should be used with cameras which do not allow the lens to be removed.&nbsp; The image below shows results on the edge of a serrate denarius (top right).&nbsp; The right part of the close up was shot with a one element cheap diopter.&nbsp; The left part used a very high grade multi-element accessory diopter.&nbsp; Single elements can not correct chromatic aberration so you get some color fringing.&nbsp; You get what you pay for. </p><p><img src="http://www.forumancientcoins.com/dougsmith/chroma.jpg" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /></p><p><br /></p><p>Extension tubes have no glass and reduce the quality very little (depending on the lens design, possibly none).&nbsp; They go between the lens and the camera so can only be used on interchangeable lens models.&nbsp; Only buy models with electric contacts (brass pins in image of this Canon model) so your auto diaphragm still works.&nbsp; </p><p><img src="http://www.pbase.com/dougsmit/image/81666283.jpg" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /></p><p>&nbsp;The other (much cheaper) type can be used with manual lenses (like enlarger lenses) to good effect (especially for very large magnifications) but it takes some care to learn to use them. Examples:</p><p><img src="http://www.pbase.com/dougsmit/image/132290945.jpg" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /> </p><p><br /></p><p>Extenders (1.4x, 2x usually) have glass and magnify both the image and the faults of the lens.&nbsp; Some do better than others but the main reason people use them is to get a telephoto lens cheaper than buying a real one.&nbsp; You could use one with a short macro lens to turn it into longer macro and get the advantage of the greater working distance.&nbsp; I have done it with very small coins but usually the quality loss is about the same or greater than just cropping.&nbsp;&nbsp; I do not recommend them. </p><p><br /></p><p>The rules have really changed in the digital age.&nbsp; Sharpening routines, properly used in postprocessing, can improve some lens problems.&nbsp; Misused, they can wreck images.&nbsp; Focus stacking can make depth of field problems much less a problem.&nbsp; I am not saying that learning all the tricks will mean you can use lousy lenses but I&#039;m wondering if that might be coming to a generation in the not so distant future.[/QUOTE]</p><p><br /></p>

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