close-up lens' versus extension tubes

Started Aug 20, 2012 | Discussions thread
Nass
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Re: another example...
In reply to Olaf Ulrich, Aug 29, 2012

Olaf, thanks, very interesting test -- news to me also. Only thing is for completeness sake on this test is there any chance of testing like for like, ie comparing diopters and ETs using completely the same optic?

Olaf Ulrich wrote:

Dave Martin wrote:

Can you post or point to a similar test of a diopter lens on a normal lens that does not show this effect?

http://www.ulrix-photo.de/misc/closeup/en/closeup.html

This web page compares the results shooting a flat subject with three 50 mm lenses on an APS-C-format DSLR camera at 1:3 magnification:

  1. Dedicated 50 mm macro lens

  2. 50/1.4 lens with +5.8 dpt close-up diopter lens

  3. 50/1.4 lens on a 17 mm extension tube

The combination #3 yields good center sharpness and definitely is good enough for most typical three-dimensional macro subjects, but clearly falls off in the corner for a flat subject. In contrast, combinations #1 and #2 are almost equally good, with perfect sharpness from center to corner.

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