Zeiss ZM 50/1.5: is this focus shift or something else going on?

[lct]

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29 minutes ago, Kl@usW. said:

Zeiss seems to adjust the lens for F 2 at 1m [...]

This same lens has been adjusted in the past at f/1.5 or f/2.8 as well. I had a choice between f/2.8 and f/1.5 myself and chose f/1.5.

[Keith (M)]

Bought mine prior to the f1.5 optimisation choice so with mine f2.8 is the 'sweet spot'.  Using it on my M7, if I want /need to use f1.5 I've learnt to focus then lean forward very slightly - works for me  

[Kl@usW.]

vor 23 Stunden schrieb Pyrogallol:

Does that mean that they expect the majority of users will be using the lens at f2 and 1 metre ?

No. I think they know  that the focus shift problem vanishes beyond 2-3 m and apertures smaller than 4. So if you want to use the lens for close portraits and wide open the information about the front focus/ back focus is helpful. 

Many years ago I was the proud but desperate owner of an Apo Summicron 90. Proud because it´s such a fantastic lens, desperate because  I always got sharp ear lobes instead of sharp eyes. Took the lens to Solms with my M6 several times ( I lived not far away) ---they checked the combo  and told me it´s OK. I wish they had cared to tell me about the terrible back focus of the lens wide open in portrait distance.... The Apo Cron 90 became the shelf queen until I sold it.

 

[hmzimelka]

17 hours ago, Keith (M) said:

Bought mine prior to the f1.5 optimisation choice so with mine f2.8 is the 'sweet spot'.  Using it on my M7, if I want /need to use f1.5 I've learnt to focus then lean forward very slightly - works for me  

One has the great benefit of a f/2.8 adjusted lens in that simply unscrewing the retaining ring, sliding out the optical cell, and removing one of the thinner shims, will shift the focus optimisation towards that of wider apertures. Its certainly easier to remove these shims and keep them as spares than it is to source new ones 

[escimo]

Maybe of some help:

https://yukosteel.wordpress.com/2018/07/02/disassembly-carl-zeiss-c-sonnar-t-50mm-f1-5-zm-lens/

[Infantasy]

I bought this lenses recently and should be optimised for f1.5. I also notice focus shift at f4. You may try f5.6 next time for better focus.