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Where is the limit.

 
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soldevilla



Joined: 16 Dec 2010
Posts: 466
Location: Barcelona, more or less

PostPosted: Wed Nov 22, 2017 10:54 am    Post subject: Where is the limit. Reply with quote

After enough time and enough photos, I do not get quality photos of minerals below two millimeters of field. I have lenses that I know are not top of the range, x10, x20 and x40 Nikon, but I do not get sharpness. Is it something that happens to everyone or am I who have not yet discovered the secret ???

Attached a cut to 100% of an image and the reduced version. Field of 1,6mm. At that size the image can still be seen, but if I want to get an impression or a publication in A-4, the result is not acceptable.

Only at the level of curiosity, this image is obtained with a finite nikon x10 objective in front of a Vivitar 100-200 telephoto lens. If I do not use the Vivitar, the chromatic aberrations and the violet haloes destroy my image.




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rjlittlefield
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Joined: 01 Aug 2006
Posts: 18248
Location: Richland, Washington State, USA

PostPosted: Sat Nov 25, 2017 9:05 am    Post subject: Reply with quote

Pixel-level sharpness at x10, x20, x40 is hard to get, mainly because of the small effective apertures that cause diffraction.

In your case there is also an issue of spherical aberration that is introduced by using a finite objective as infinite. I expect that essentially you are trading reduced chromatic aberrations for greatly increased spherical aberration that kills contrast for fine details. See http://www.photomacrography.net/forum/viewtopic.php?p=59673#59673 for my experience in testing a finite Nikon CF N objective on 200 mm telephoto, and compare against the same lens on bellows shown at the start of the same thread, http://www.photomacrography.net/forum/viewtopic.php?p=59589#59589 . A similar test with your own equipment might be informative.

I think the only good method for handling subjects like this is to use apochromatic lenses, such as the Mitutoyo M PLan Apo series. They are expensive, but the reduction in false color is dramatic. See http://www.photomacrography.net/forum/viewtopic.php?p=147672#147672 for comparison.

--Rik
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