Lotusm50 Offline Image Upload: Off
Registered: Sep 26, 2005 Total Posts: 3275 Country: United States

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Re: Please help in finding bad CA on my ZF lens | |
rfkiii wrote:
Earlier this year, I bought the 25 ZF but had a problem with undue softness encroahing well inside the edges that even f16 couldn't tame. I suspected the adaptor (Liliybox) but at the time did not have enough experience with these matters to be 100% sure it was the adaptor so returned the lens while still within its return period.
The ZF 25mm is a curious beast. In some ways it is a stellar performer in other ways it seems to fall flat. In some respects, according to communication from Zeiss, its design was done to optimize performance for an APS-c sensor -- not full frame even though the lens covers full frame. Further, they make a point of the making the lens focus closely, yet seem to do little to optimize its performance at close focus (e.g. no floating element) with Zeiss suggesting it's use at close focus would be for "atmosphere" (which to me is a cop-out rationalization for bad performance). Zeiss could have done a lot more with this lens. I was originally quite interested in this lens, but no longer as it ultimately disappoints.
Here is the relevant text of the comments I received from Zeiss on the ZF 25mm:
In spite of the close minimum focus distance the lens has no floating elements. So the close focus is not intended to be used for copy work. It is for three-dimensional subjects, where there is a main part in the centre and the rest is just "atmosphere". It allows very dynamic pictures of small things, very different from the distant view of typical macro lenses. And in this kind of subjects field curvature is no issue. Testing the lens with flat targets reveals the typical weaknesses, but it is far away from many practical applications.
The close focus capability is also a kind of historical footnote, since the "great grandfather" of this lens for the Contarex had the same feature. The design is of course new, and we particularly looked for improved field flatness within the APS area.
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