The 28mm Distagon ZF is the best kept secret of the ZF lens program. Overall it is a powerhouse of a lens, with particularly excellent treatment of color, but some issues at full aperture have kept it in the shadow of more consistent lenses in the series. This Distagon is an excellent choice for a normal lens on APS-C cameras and a demanding (but rewarding) high-speed wide-angle on full-frame cameras.
This Distagon is quite closely related to its Contax predecessor, one of the pioneering designs for floating elements in wide-angle designs. The new design improves performance at the maximum aperture substantially while keeping other parameters largely unchanged. As a result the new lens inherits high and low points from the advanced Contax design.
The 28mm Distagon ZF was a happy surprise for me. I delayed testing it because I anticipated problems and enjoyed my 35mm Distagon too much to feel the need to overcome them. In the end I enjoyed this lens a lot and can now imagine using it in addition to, or even in place of, a 35mm Distagon.
Once again I want to thank Roger at LensRentals.Com for allowing me to review this lens. Double thanks for letting me hold on to the lens for an extra week.
The 28mm ZF is of average size and weight for a ZF lens. As in almost all things, it sits between the 35mm and 25mm lenses and could easily be confused for either by sight or by touch (I made this mistake at least once). Like these other lenses on the D700 the combined pair is slightly rear-heavy but comfortable, and far more portable than most other lenses.
Manual focus is quick and decisive with this lens, with a rate of focus that is ideal for use in photojournalistic use. Unfortunately at full aperture accurate placement of focus for emphasis in the other regions requires special attention and skill, due to (very) strong field curvature. This issue is compounded by the poor quality of the D700’s manual focus assistance in the outer regions.
The 28mm ZF extends slightly when focusing. A floating group at the rear helps to maintain image quality in the close range, down to 0.24 meters.
The 28mm ZF draws outstanding colors, at times giving you the impression that you are shooting at the golden hour while standing in middling afternoon Sun. Besides its great color output, the 28mm ZF is a high performance lens with one key flaw: it exhibits strong field curvature. For this reason (mainly) its other strong suits are only revealed at smaller apertures.
Wide-open sharpness is high and micro-contrast is good (but not great) over almost the entire frame. This is a little-known fact which is revealed by careful focus in live-view mode, but is well hidden in actual use due to large amounts of field curvature. Obviously this fact is also hidden in laboratory tests that use flat resolution charts.
More typically, and under test conditions, only the central region of the frame (or the selectively focused region) has high sharpness and good micro-contrast at the maximum aperture. The outer (or other) regions then are drawn in defocus and with strong aberrations (coma and astigmatism) that further degrade image perception.
Stopping down to f/2.8 improves micro-contrast to excellent levels over a good portion of the frame -- in fact this lens thus produces some of the best micro-contrast I’ve seen yet! This stop also mitigates field curvature for many uses on full format sensors. On APS-C sensors image quality should be unreservedly excellent starting from this aperture.
Stopping down further to f/4 improves image quality at infinity on full format sensors, which now suffer very little from field curvature, and then not at all at f/5.6. Image quality at f/5.6 is excellent for all uses on all cameras.
Outside the (curved) plane of focus, aberrations play various roles against image quality. Coma, astigmatism and longitudinal CA combine to produce some very ugly Bokeh at times – this is one lens which does not pass the “backlit foliage” test for example. This is something to be aware of and can be a problem, but luckily stopping down to f/2.4 or f/2.8 improves things dramatically. Bokeh quality becomes very high around f/4.
Lastly, the 28mm ZF is a poster child for the extended Zeiss T* family of lenses when it comes to color and global contrast. Resistance to veiling glare is high. Resistance to internal reflections is good – though it can produce curious looking flare spots against the Sun.
The 28mm Distagon ZF is often overlooked because of its reputation for high levels of field curvature that reduce its effectiveness at f/2 on full-frame sensors. There is no denying that this is a low point for the lens, but with so many high points there is much to redeem it also. At the very worst, one could think of it as a splendid 28mm f/2.8 lens.
Would I recommend this lens to other photographers? Yes. Especially APS-C users.