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What Happens if the Sensor is not Exactly Plane Parallel to the Lens Mount?

Four lenses with skew, two camera bodies (Nikon D800E, D800 both previously adjusted).

To my review of the Zeiss 135mm f/2 APO-Sonnar in Guide to Zeiss is added an example of what happens when a camera system does not have everything perfectly aligned.

Such problems are particularly acute with high megapixel cameras plus high performance lenses and infinity focus. I’ve seen it with every brand now, and it’s super frustrating.

A comparison with the Nikon 135mm f/2 DC now follows. It shows the same issue, but this does not prevent unequivocal conclusions from being drawn about its performance relative to the Zeiss 135mm f/2 APO-Sonnar.

According to Nikon, specifications and tolerances for the flange distance and similar are not made public. My suspicious is that tolerances are too loose for a 36-megapixel sensor. Based on MTF through-focus graphs I’ve seen, there is room for no more than 5 microns of variation from corner to corner at f/2.8, a figure that might be unattainable by mechanical adjustment.

Nikon D800E + Zeiss 135mm f/2 APO-Sonnar @ f/2.8
Nikon D800E + Zeiss 135mm f/2 APO-Sonnar @ f/2

Michael M writes:

I have been paying much closer attention to your site as subscriber as I begin to re-engage with photography. After giving up my Hassy's, Leica's and Ebony 4x5 film systems I quickly became disinterested in the digital world given the huge optical shortcomings vs. emulsion-based systems. I concluded back in 2005 that digital was a real stinker and I was never going to get the Zeiss or Leica feel to an image. My stomach still churns when I see chromatic aberration, though I have learned to scrub out most of it.

Within the past year, things are getting good enough again and digital darkroom tools and related necessary MW's of processing power are now reasonably accessible that I have begun to re-engage, in particular with the micro 4/3 world. Your frequent, thorough and thoughtful analyses - full frame and otherwise - are terrific; they pay out pros and cons and always remind us the balancing act that makes a camera tool rather than a "be all, end all" device. Most recently, your article on the lens mount alignment tolerance issue impairing the resolution of the new 36mp and above sensors is timely. I suspect we are seeing the design process in the major makers fragmenting: different subsystems are all striving for "break out" advances that the marketing folks can spin without thought as to how these advances work or often do not work with other subsystems. Sadly, very very very few users and even fewer writers and critics have the technical chops to shine the light where it belongs. Thus, thank you for doing so! It will be fascinating to see if and how the "interchangeable" lens world comes to grip with the notion that you might very well need a more robust mount or fixed mount approach so great glass can help the new sensor refinements bring out the best image. DP2 looks very interesting form that perspective, but is still in clunky Version 1.x mode I think.

Anyway, enough prattle: thanks for the great great product you produce.

DIGLLOYD: My Nikon D800E is off to Nikon. Maybe it really is off (just a little) and maybe it will be rectified— I don’t know yet.


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