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We recently acquired specifications for all DSLR lenses by Carl Zeiss and almost always the Canon EF-mount version is larger and heavier than the Nikon F-mount version. The difference ranges from small (20g / 1mm) to large (120g / 8mm) or up to 20% difference by weight and 12% by dimension.

Is there a technical reason why there should be a difference in size? Both always cover the same full-frame imaging circle and have the same optical design, number of elements, etc. Would image quality be affected by such differences?

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1  
Which lenses have the largest difference in weight? –  Matt Grum Apr 27 '13 at 10:28
    
I would like to know the same thing Matt asked. Could help a lot in offering a valid answer. –  jrista Apr 28 '13 at 4:45
    
By weight, it is the Zeiss Distagon T* 2.8/21. By volume the Zeiss Distagon T* 2/35 and Zeiss Distagon T* 2/28. –  Itai Apr 28 '13 at 14:57

3 Answers 3

up vote 4 down vote accepted

Wikipedia lists Canon's (outer) throat mount diameter as 54mm vs. Nikon's at 44mm. This means, at the mount, there is an extra 31.4mm of circumference on a Canon lens vs the same Nikon lens (assuming the lens is throat-diameter-limited) that has to be made. Depending on how Zeiss chooses to incorporate this extra girth in the packaging of the lens, the amount of additional size and weight will vary.

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The circumference of a 54mm wide circle is 169.6mm, that of a 44mm diameter circle is 138.2. The difference in circumference is 31.4mm. –  Michael Clark Jul 2 '13 at 14:53

A small part of the differences can be accounted for by the shorter flange distance for Canon. For the same sensor to rear lens element distance the EF mount version must be 2.5mm longer than the Nikon version at the back of the lens. The Canon mount diameter is also 54mm across, compared to 44mm for Nikon, so the lens may need to be larger in circumference. The additional materials involved would add to the weight of the lens.

Depending on the focal length, many of the Zeiss lenses have a built in hood that is an appreciable part of the lens' length. This may vary from one mount to the next. Between Nikon, Sony, and Canon the Full Frame sensor height varies between 23.9-24.3mm. Thy are all 36mm wide. Zeiss appears to optimize each version of the lens for the mount with which it is compatible, so this may come into play as well.

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I'm a Nikon guy, but from what I know the Canon EOS system puts the AF motors in the lenses, not the bodies. So all EOS lenses that autofocus will need to have an AF motor built in. Maybe that's where the weight difference comes from, because all the top Nikon bodies have AF motors built in, so only need the focus drive shaft coupling. Presumably, entry-level Nikon owners with non-AF bodies aren't going to be buying expensive full-frame 3rd-party lenses like Zeiss.

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3  
It's a good theory, but Zeiss lenses for Canon and Nikon mounts are all manual-focus. (Not even screw-drive.) –  mattdm Apr 26 '13 at 23:44
    
Downvoted since Zeiss ZE and ZF/.2 are manual focus. –  bRad Gibson Apr 28 '13 at 2:02
    
-1 because "all the top Nikon bodies have AF motors built in" is simply not true. –  Olin Lathrop Jul 2 '13 at 23:28

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