Carl Zeiss Distagon T* 3.5/18 ZF lens review

Introduction Carl Zeiss "ZF" line of lenses was introduced in January 2006. The lenses feature manual focusing and are designed to be used on Nikon F mount cameras. The original ZF lenses come with the features that users of the classic Nikon SLR cameras expect to have: Nikon F bayonet, automatic close–down aperture, the same rotation direction of focus and aperture ring, second aperture scale to enable optical readout of the aperture in the viewfinder and AI coupling fork. The lenses, however, do not have any electronics and thus there is no electronic communication with the camera. In practice this means that one has to input lens data (focal length and maximum aperture) in the camera and set aperture on the lens.

In November 2009 the original ZF line was upgraded to ZF.2. The updated lenses no longer have the pre–AI coupling fork, due to which light metering cannot be used on older Nikon cameras (F, F2, Nikkormat, etc.). Very importantly, however, they boast electronic interface thus allowing full support of automatic exposure modes and inclusion of lens–related data in EXIF. At the same time, ZF.2 lenses have a mechanical lock on the aperture ring to lock the aperture ring at the smallest aperture setting. There is no difference between ZF and ZF.2 lenses in terms of optics.

The lens was tested on a 12MP Nikon D700 camera. FX format cameras of higher resolution will put a further emphasis on some of the performance deficiencies reported in the review. At the same time, vignetting, distortion and corner sharpness will be less problematic when the lens is used on DX format cameras.

Build quality, focusing and handling

The lens is made of metal and built like the proverbial tank; every aspect of its construction exudes quality. Operation of the focus ring is smooth and buttery; operation of the aperture ring, on the other hand, is fluid yet firm. Front element does not rotate as you focus the lens, which makes using polarizing and graduated ND filters easy.

Of and by itself, the lens is neither big nor small, neither heavy nor light (470g). To put it into perspective, it is roughly in the middle between the Zeiss 2.8/21 ZF/ZF.2 lens and Nikon's smaller AF–D prime lenses (e.g., AF Nikkor 28mm f/2.8D) in terms of both size and weight. When mounted on a camera, the lens–and–camera combo feels somewhat bulky because of the uncommonly large front of the lens. The lens takes 82mm filters, which is an unusual size and might require buying additional filters specifically for this lens.

Sharpness

It is understandable why most photographers usually put more emphasis on sharpness than on other optical performance factors—while such aberrations as distortion, vignetting, etc. will be seen only in some images and, at least partially, can be dealt with in post processing, soft corners will be visible in most, if not all, photographs and cannot be remedied after the fact. Thus, let us first see how the lenses perform in the department of sharpness. The images below are crops from the original test shots shown at 100% magnification; no sharpening was applied to any of them.

Centre

Corner

f/3.5

f/8

The test shots and my overall experience with the lens indicate that it is impeccably sharp, centre to corner, starting right from f/3.5—to the extent that it can be used as a benchmark for evaluating other lenses. If you resort to hardcore pixel peeping, there is a very slight loss of sharpness and contrast in the farthest corners at f/3.5; this, however, is unlikely to be noticeable in reasonably sized prints.

Vignetting

The test shots below were taken at the same EV (exposure value). The lens apparently has a small image circle and shows very strong vignetting at f/3.5 (keep in mind that f/3.5 is only 1/3 stops faster than f/4, which means that we have a lot of vignetting at a pretty slow aperture). At this aperture the aberration will be seen in most real life photographs; it is very difficult to completely remove in post processing but can be reduced to a level where it is less objectionable.

	f/3.5		f/5.6		f/8

Vignetting is still quite noticeable at f/5.6 and is reasonably controlled only by f/8.

Distortion

As can be seen in the photograph below, the lens exhibits predominantly pincushion distortion that has a slightly complex (wavy) signature (pay attention to the yellow line at the bottom of the image—the line is supposed to be straight). Its degree, however, is very low and you will not see it in most photographs. In fact, given how wide the lens is, one has to go out of his way to find pictures where the aberration is noticeable.

Chromatic aberration

Chromatic aberration is very well controlled. Small amount of colour fringing can be seen around high contrast edges; rather than being a thorn in the eye, however, it is something that you have to know how to induce and purposefully look for. Colour fringing is manifested as lateral chromatic aberration that can be easily removed in post processing; I could not detect any immediately visible longitudinal chromatic aberration. Below is an example of the worst (yet still very minor) chromatic aberration that I have seen from this lens.

Colour fringing: unprocessed on the left, removed on the right

Flare

The lens is very flare resistant, which is quite impressive given the lens' fairly large front element and how complex the lens is optically (13 elements in 11 groups). I purposefully tried to induce image degradation from flare by shooting into bright sources of light, but only managed to get relatively minor ghosting.

Bokeh

The Carl Zeiss Distagon T* 3.5/18 ZF is an ultra wide angle lens that, as mentioned above, is not exactly fast. Thus, bokeh will not be of a major concern in most situations. Nevertheless, if you are interested, bokeh is fairly neutral at f/3.5 (i.e., it is not distracting, yet not too pleasing to the eye) and very smooth at smaller apertures.

Final thoughts

Carl Zeiss Distagon T* 3.5/18 ZF is a great optic and its performance is perfectly in line with what one expects from Carl Zeiss. The only gripe that I have is that it is a relatively slow lens but, even so, still has very strong vignetting wide–open (but then again, many ultra wide angle lenses have this quality). If you need a lens of this focal length and do not mind this caveat, I recommend it without reservations.