PHOTOOG Photography writings by Olivier Giroux

8Jul/085

Disappointing update for the ZF 18mm Distagon

We now have MTF available for the Zeiss ZF 3.5/18 Distagon T*, previously discussed here and here. I don't how Diglloyd got the chart PDF, but he's got it.

**Added**: this now also posted on the Zeiss website, here.


Hrm… let’s talk to this chart...

Comments from Diglloyd...

“The MTF graphs […] look quite promising, showing very high contrast, suggesting that performance is near optimal wide open.”

…if you only like sagittal detail, I guess. The high contrast doesn’t seem to apply to tangential details, which even appear relatively worse when the lens is stopped-down.

I agree with Diglloyd, wide-open the lens starts off looking promising, but the gap between sagittal and tangential detail contast (stopped-down) is too important for this league of product. Now if this sounds like a dry theoretical opinion... if sagittal contrast was the determining factor of performance, wouldn't you expect this sample (below) to pop a lot more?


Sample put up by Zeiss in this directory. It's frustrating that Zeiss did not include any samples from which to easily judge sharpness.

Looking at the sample closely I conclude we're seeing detail smearing in the upper right corner. This is consistent with the posted MTF.


Corner 100% crop. Blah-quality.

I first hoped the test shot was taken at f/3.5 and wouldn’t be indicative of maximum performance, but now we know the corner performance is independent of aperture...

In the end, with its completely new optical formula the ZF Distagon-18 does improve greatly on the MM Distagon-18 but only to net a bias for the orientation of detail. This is rather short of success in my opinion. It is miles behind the MM Distagon-21, which offers even better performance that is independent of orientation.

It’s clear to me that Zeiss will eventually ship a ZF 2.8/21 Distagon, having shipped a 2.8/21 for every other system they supported. I’ll stay put and hope they deliver a home-run like the MM 2.8/21.


Comments (5) Trackbacks (0)
  1. I don’t understand what your point is. We only have some low-level pictures from this lens that makes it impossible to give any serious comments. Why can’t you just wait until you see better pictures?

  2. The MTF chart is quite valuable in this respect, and it’s quite clear too. The chart is worth 100 test images.

    Some of the best wide-angle lens images are found here (http://www.16-9.net/lens_tests/), particularly the collection under the 14-24 review. Compare what you see there with the published MTF charts for the lenses tested. The charts describe quite clearly what the images also show.

    Consider also the DPReview review of the Nikkor 70-200 VR. The review reveals the lens is incapable of resolving detail in the corners – everyone was shocked. Except the MTF chart posted at the lens’ original launch clearly says the same thing.

  3. Experience with the lens so far — and you can see example posted around the web — indicate that it is an exceptional performer. It is much better than the old Contax Zeiss 18mm f4.0 Distagon and some have compared it’s quality as approaching the Zeiss 21mm f2.8 Distagon. And better than the Canon and Nikon zooms at the focal length. Your evaluation here and your interpretation of the MTF imply that this is a weak performer. However, the evidence to date suggest that is not the case. The Zeiss ZF 18mm is proving to be an exceptional lens.

  4. Hi Bob, can you point me to online discussions to this effect that include image samples? I know Lloyd Chambers got his copy of the lens, but I haven’t seen him comment on the performance yet.

    Comparisons to the MM Distagon-21 should not be made lightly… I mean if true then that’s _super_ but mark me skeptical.

    I think the Nikon 14-24 is likely going to remain the reference at 18mm for a little while longer.

    But hey, I can’t wait to be proven wrong!

  5. Here’s a review of the Zeiss 18
    that indicates it is less than
    a stellar lens:

    http://slrlensreview.com/content/view/498/51/

    maljo


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