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For landscapes that require you to actually walk to get there (!) giant tele lenses are a big problem, no pun intended, and no IS gets near a tripod image. Which outs the tele zoom set for me at least. Sony make a great 70-200 also but it is huge.
Thanks AhamB, I saw those tripod collars but they all refer to a f4.5 lens, which I thought might be yet another lens, but checking the Contax list I see no other. If so, that would assist greatly in consistently sharp images. The only place for a collar is at the front of the lens it seems - unless you attach it just in front of the aperture ring, over the focal length scale? Maybe an oversight on Zeiss's part, for such a slow lens would be hard to handhold at decent shutter speeds.
I like the zebra MTF test, which the Canon passes with flying colours, although it looks more like 2 lp/cm than 40 lp/mm - hah.
Back to the 100-300, sadly it extends in linear fashion - 100mm in retracted form, 300mm at full extension, unlike the 35-70. Happy to be wrong about these things.