Adapter causing backfocussing?

[mfogiel]

I have made some test shots lately, to see how my fast lenses perform wide open, as I would like to do more portraiture.
Strangely, I have found that the biggest misfocussing happens with a Canon 50/1.2 and Summitar 50/2, which are both sharing the same adapter, and both front focus quite consistently. This has prompted me to believe, that perhaps the adapter I am using is too thick - has anybody experienced a similar problem, and if yes, what would be the "thin" alternative adapter, if it exists?
Thanks
Marek

 

[rxmd]

I assume you are talking about adapters to Leica M, about focusing the lens wide open, and about close distances.
Also you mention front focusing in the text, and back focusing in the headline. I assume you mean front focusing, in which case the adapter would indeed be minimally too thick. It would be interesting to know by how much the lens is front focusing. A centimeter at 1m wide open? Ten centimeters?

Anyway, what brand adapter are you currently using? The tolerances here are quite strict, it happens easily that an adapter is too thick by a few hundredths of millimeters.

 

[colyn]

My experience with the off brand adapters is that they are either too thick or too thin. I have since gotten rid of all except for the original Leitz versions and no longer have focusing issues.

 

[mfogiel]

Sorry, the title is wrong, it should read front focussing - both these lenses front focus about 4cm at 1m. I don't have the adapter with me now, will check on the brand this evening.

 

[ath]

If you are talking about 50mm LTM lenses adapted to M-Bayonet a wrong thickness of the adapter will lead to a disagreement between actual focus and distance scale. But rangefinder and actual focus will agree.
Reason: for 50mm lenses the RF cam travels the same amount as the optical block of the lens; if the adapter is too thick both are offsetted by the same amount and this cancels out.
Other than 50mm the story is different.

 

[Brian Legge]

I tried a generic adapter for a 90mm lens. It didn't focus to infinity and the focus didn't match the rangefinder throughout.

I ditched it and switched exclusively to Voigtlander adapters. I haven't had any issues with them.