CV Nokton 35/1.4 - focus issues

[karlukov]

hi everyone

i have a very strange and very annoying problem with my cv 35/1.4.
when shooting wide open focus is where it should be, from 1m to infinity.
but starting from f/1,7-2 to f/8 lens shows awful back-focus at close and middle distances - oof spot at center and blurred corners (dissapears at f/5.6 and smaller)
far objects is okay though

a couple of months ago i noticed this problem so i gave a lens to repairman, he said that infinity was off like at 5m or something
so he adjusted a lens to my camera using collimator.

last week when i got developed two rolls of across i saw that nothing's changed - wide open is okay; stopped down it has back focus; at f/11 and f/16 - sharp enough, but can't beat even my olympus xa2

yeah yeah, i know about 35/1.4 focus shift and stuff
it just didn't seems like a shift - focusing at 2-3m using rangefinder in range f/2-f/8 i get oof image at 2-3m at the center and sharp infinity.

oh forgot to say
i'm shooting with this lens on bessa r2 and bought it used without box and papers from epson rd-1 user
judging by his shots he didn't suffer from this problem.
it's my only leica-m lens - all other lens are ltm via leica-m adapters (soviet Jupiter-3 50/1.5, Jupiter-8 50/2 and Orion-15 28/6), they're fine though - no problems with focus even with J-3 wide open.

i love this lens - it gives me a nice glowing images wide open.
but mainly i'm shooting street and genre photography using scale and small apertures and honestly, i'm sick of guessing if there was a right focus or not.
so, what should i do?
it needs to re-adjust or i should just sell it and get another one?

 

[rscheffler]

It does sound like focus shift.

My understanding is focus shift is worse at near distances than when approaching infinity. That lens also has a lot of field curvature, which might complicate matters when the subject is placed off center.

You could try having the lens optimized for correct focus at f/2 or f/2.8, which will balance the focus shift somewhat, but will cause front focus when shot wide open.

It might be a hassle, but I would almost consider using the Nokton for wide open shooting and get a 35/2.5 for everything else (assuming it doesn't also have focus shift problems). It's small enough, but yes, it's one more thing to carry.

 

[ferider]

It does sound like focus shift.

My understanding is focus shift is worse at near distances than when approaching infinity. That lens also has a lot of field curvature, which might complicate matters when the subject is placed off center.

You could try having the lens optimized for correct focus at f/2 or f/2.8, which will balance the focus shift somewhat, but will cause front focus when shot wide open.

Agree.

I optimized mine for f2 on my m240. That makes 1.4 front focus in the center a bit, but when you focus using rule of thirds, the cosine error compensates perfectly wide open. For critical focus, I avoid f2.8, 4, and 5.6, if possible.

Roland.

 

[karlukov]

thank you guys!

i'll try to tighten up the span ring - my lens gets a little bit wobbly
maybe sharpness problem is connected with it somehow