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November 27, 2013

Can you tame an Otus Zeiss?

Otus scops aka Eurasian Scops Owl aka Otus Zeiss (Image under Wikimedia Commons)
The ZEISS Otus 1.4/55 lens currently is the finest lens ever made for a 35mm SLR. Every test coming in from DxO, DPReview and other test sites all speak the same language: there has been no lens with a similiar performance before the Otus. Wide open at F/1.4, it beats many excellent lenses out there at F/2.8, and by F/4, it breaks most limits. Across the entire field.
     So, even at its undesirable price level, it remains a desirable item sold out for six months now. But a question remains: can you tame it?
     This question is very legit because to actually make use of the extreme resolving power you not only need a high resolving camera body (like the Nikon D800E) but also extreme luck when focusing it, it seems. This is because the Otus lens has no autofocus and digital SLRs have view finders with low magnification like 0.7x and no manual focus-optimized ground screens.

I should probably add that in order to see the merits of the Otus lens wide open,  it is not necessary to look at the center only. The improvement of corners is drastic enough to be visible with a non-perfect focus too. Nevertheless, I am curious to understand if the Otus can be focused precisely in the field.

http://www.smugmug.com/photos/i-s8zHZv8/0/O/i-s8zHZv8-O.jpg
Sample photo D800E + Zeiss Otus 55 at f/1.4, 1/125s, iso1800 available light, handheld (click for original size)

The beast
The beast to be tamed is manual focusing the Otus in the field. I.e., not using an HDMI monitor connected to HDMI and featuring peaking even with a D800E. So, I decided to do a field test.

I had the opportunity to handle a D800E with a split-prism / microlenses focus screen. However, I did not have the impression that it helped me much with the focus beyond the help I obtained from the focus assist >O< meter in the viewfinder. Therefore, I did all further tests with my own D800E which has the stock screen.

The test was handheld in available light after dark using the city lights (with no reflectors) as illumination. I tried to use fill flash but I wasn't content with the results. All samples shown here are w/o flash. Photos are processed in Lightroom, applying exposure boost, mild sharpness and vignetting effect actually, but no crop. So, you may still evaluate out-of-focus highlights but note that this is no test for charts or raw image quality. Rather, it is just meant to help me understand what I can achieve using the lens. YMMV. But as a courtesy to my readers, you may access full resolution samples by clicking the small ones.

As you can see in the above image, I was able to achieve reasonable focus. However, don't expect studio quality sharpness in this kind of situation. I am sure the lens can do better with even shorter exposure and at base iso, using critically controlled focus. But all things considered, I think the sharpness is satisfactory. Overall, the sharpness on the eye, the bokeh and highlights are beautiful. Note that the out-of-focus highlights aren't round in the corners anymore, vignetting at work where the left side of the sensor simply can't see the left side of the exit pupil, a constraint I guess which is imposed by the mount diameter.

Results
My keeper rate in the above situation was about one out of ten. This sounds low but in reality, it is surprisingly large. Let me explain. I focused using the focus indicator pointed onto the left eye (right in images) and then recompose. I watched the focus indicator and tried to make the green focus lock emerge. This was challenging for two reasons: First, the >< indicators kept flickering with the lock being hesitant. I often actually fired with both >< signs illuminated together (and no O). Second, the focus area is larger than an eye and it was too dark to even try to focus using the screen, just being happy to keep the eye in the center. Below is a crop of the left eye:
100% 1:1 crop at f/1.4, 1/125s, iso200 in a store. You can see the store reflected in the pupil.
As you can see, pixel-peeping sharpness does not even reach from eyelashes to pupil, or from the left to the right side of the pupil. No way you could tell the AF (or its indicator) what part of the eye you wanted to be in focus. This considered, to hit the pupil's center without a magnifying live view focus method was not bad.
     If you enter 8┬Ám as circle of confusion (for pixel sharpness after sharpening) and 550mm as approx. distance (for 10:1 magnification or 24cm image height), a DoF calculator returns 2mm as "depth of field" (1mm in front and behind). Which explains why as few as 3 eyelashes are sharp and the others aren't. Here is the full image the above crop is taken from:
http://www.smugmug.com/photos/i-vpFZLg7/0/M/i-vpFZLg7-M.jpg
Sample photo D800E + Zeiss Otus 55 at f/1.4, 1/125s, iso200 available light in a store, handheld (click for original size).
Note: the overall image does of course have larger depth of field (8mm actually).

So yes, it is possible to tame a Zeiss Otus 55 lens in the field, using manual focus and wide open. Even in low light. But be prepared to have a lower keeper rate than normal as the focus simply won't be as quick. Even when tamed, the Otus remains a wild animal. In my case the keeper rate was 10% but with more practice, it may improve a lot. Of course, I don't even think of shooting a moving subject this close at f/1.4 with manual focus.

While in the studio, where the Zeiss may actually exploit its overall resolution advantage, if used wide open in the field at f/1.4, its bokeh, good contrast and corner sharpness may actually be equally important arguments for this lens. It would be interesting to compare shots from a competing lens in a similiar situation (I did not). So, let me conclude the article with another sample image for the fans of her.
http://www.smugmug.com/photos/i-HJXKdbn/0/O/i-HJXKdbn-O.jpg
Sample photo D800E + Zeiss Otus 55 at f/1.4, 1/125s, iso200 available light from shop window, handheld (click for original size)
Thanks for reading,

Falk

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