See Making Sharp Images for extensive coverage on maximizing image sharpnes (lenses, technique, diffraction, etc).
Read my comments on the tolerances and technique required to exploit the 36MP resolution of the Nikon D800 / D800E.
What are the requirements for a lens that can be considered not just good enough, but excellent for use with a 36 megapixel sensor?
Assuming exacting camera tolerances and excellent technique, here is what a lens must offer to be optimal on a 36MP sensor:
- High resolving power with high contrast = high MTF. The fine pixel pitch of a 36MP sensor demands very high contrast for the finest details.
- Low field curvature — designs with significant field curvature become even more problematic than they already are, yet stopping down to mitigate field curvature will kill contrast from diffraction (both topics addressed in Making Sharp Images). Fast lenses, even the most expensive ones with the red dot on them, often have significant field curvature. With some lenses, focusing at infinity requires f/8 to produce edge to edge sharpness— with an 18MP camera!
- Sharpness over the whole frame — here, even new designs have their limits when the edges and corners are approached. Espeically for wide angles, few lenses deliver full sharpness corner to corner. There are a few exceptions.
- Color aberrations. While lateral chromatic aberration can be corrected in software, it remains highly undesirable, and can impede Live View focusing when strong enough. Axial chromatic aberration is much more problematic because it interferes with focusing, making exact focus ambiguous, as well as polluting the resulting image with lower contrast and/or purple fringing.
- Accurate focus. This means using Live View with a loupe. And it means that manual focus lenses with manual focusing helicoids are even more useful than ever before. Many autofocus lenses are to work with for manual focus because of overly sensitive or twitchy focus throw for fine adjustments.
Zeiss ZF.2 lenses for Nikon
Here I will nit-pick on Zeiss lenses for Canon and Nikon, which are my preferred* lenses. These comments are strictly in the realm of obtaining maximum sharpness, sharpness is only one aspect of a satisfying image.
Thank you for buying Zeiss lenses using the links on this site.
A brief assessment of the currently Zeiss ZF.2 lineup. Lenses in bold are recommended as having the best potential for maximum performance on the 36MP Nikon D800 or similar high-resolution DSLRs.
- Zeiss 18mm f/3.5 Distagon — chromatic errors need improvement, field curvature at infinity can be readily observed, cyan color cast towards the corners.
- Zeiss 21mm f/2.8 Distagon — should carry forward nicely, but will likely show some limits that are not apparent at 21 or 24MP, including some traces of chromatic errors.
- Zeiss 25mm f/2 Distagon — perhaps the best 24/25mm lens available, but optimized for central 3/4 of frame, and thus still not strong enough at the edges and corners, interacting with mild field curvature. Central 3/4 of the frame should perform really well on 36MP sensor. Outstanding color correction might nonetheless show a trace of weakness on 36MP, but it’s the best of the best 24/25mm nonetheless.
- Zeiss 25mm f/2.8 Distagon — field curvature and chromatic errors need improvement (close range), but otherwise very sharp and contrasty, will hold up well overall to 3/4 of the frame.
- Zeiss 28mm f/2 Distagon — field curvature and chromatic errors need improvement. Edges and corners could disappoint on 36MP.
- Zeiss 35mm f/1.4 Distagon — will hold up well on 36MP, but as shown in my Zeiss Guide. Mild field curvature, and some axial color makes pinpoint focus a bit harder than with an f/2 or f/2.8 lens.
- Zeiss 35mm f/2 Distagon — great sharpness, but chromatic errors are too high for a 36MP sensor, and edges/corners might be more of an issue. Prone to color fringing with small photosite cameras.
- Zeiss 50mm f/1.4 Planar — moderate field curvature (which is also the case for just about every 50mm lens of the dozen I own). Focus shift from spherical aberration is already a challenge for a 24MP sensor. Will require careful focus, but if done properly, will deliver very high resolution.
- Zeiss 50mm f/2 Makro-Planar — field curvature as edges and corners are approached, which is odd for a macro lens. And limiting for full-frame sharpness.
- Zeiss 85mm f/1.4 Planar — focus shift from spherical aberration already makes it a challenge when focusing wide open and shooting at f/2 - f/5.6, especially at close range.
- Zeiss 100mm f/2 Makro-Planar — outstanding sharpness, but needs better axial color correction to reduce purple halos in the f/2 - f/4 range, as well as background color cast. Still, this lens is likely to produce the best sharpness in the entire ZF.2 line.
There you have it— even top-grade glass has plenty I’d like to see improved! Don’t take these comments as suggesting there are clearly better alternatives. If there were, I’d be shooting them!
The question is whether there is a middle ground between a $25,000 cine lens and a lens for a DSLR that is not too large and heavy (make a lens large enough and expensive enough and most optical issues can be addressed). Note that the recent Zeiss designs (21/2.8, 35/1.4 and 25/2) have already become more highly corrected than predecessors, with correspondingly higher prices. I would like to see Zeiss take that approach still further, even if it meant greater cost, since owning fewer better lenses is preferable to more lesser lenses.
* When I say the Zeiss lenses are my “preferred” lenses, I mean just that. I am not claiming that they are always the sharpest— they aren’t. Both Canon and Nikon have many excellent lenses also (and some duds). But the image that results from a lens, the way it draws is not something that comes down to a single sharpness value; it is a mistake to think that sharpness is the sole criterion for choosing a lens. By way of example, the Zeiss 25mm f/2.8 Distagon is poorly corrected at close distance, not very sharp, and yet it might still be my favorite lens for what I’d term “artistic” work. Ditto for the Zeiss 85mm f/1.4 Planar, and this is by design (class computation for portraiture). An artist doesn’t use just one brush, nor should any photographer looking for a particular style of rendition.