M8 Focusing with CV screw mt lenses !

[D&A]

Hi All,

I was trying out two Leica M8 bodies which focused perfectly at infinity with all the Leica and Zeiss M mount lenses (of all focal lengths I tried...focusing on objects 1/4 to 1/2 or more miles away.

In contrast all the CV screw mount lenses (with CV adapters) on these two bodies were able to focus past infinity as judging by the rangefinder patch in both M8's . It's hard for me to imagine all thoses screw Mt CV lenses I tried all needing recollimation (for infinity) or the various CV mounts with these lenses being machined slightly wrong...nad since both M8's focused at infinity perfectly with all Leica and Zeiss lenses...I eliminated them as the culprits. So has anyone observed this (focusing past infinity) with screw mount CV lenses used with CV adapters, specifically on an M8 body?

No other adapters were on hand to try (such as Leica's). If it was all thioses CV lenses in use with their Cv adapters acting this way on M8 bodies....I assume re- colloimation of the lenses has to be done by a qualified tech?


Thnaks in advance for your observations with your own M8's and CV lenses.

Dave

 

[Bryce]

Sounds like the adapter is too thin... Not a good policy on the part of CV if true.

 

[Bob Parsons]

Yes, I have a 50/1.5 Nokton which will focus past infinity according to the rangefinder patch. However when the M8 rangefinder shows coincidence on a very distant object the image from the lens is also in focus. With my lens it looks as if the focus helical is able to take it a fraction past infinity. The lens cam and screw adapter must be in spec otherwise the rangefinder and image focus would not agree.

I'll add my 35/1.2 Nokton also focuses fractionally past infinity and that doesn't have a screw adapter. Again when the rangefinder shows coincidence a distant object is in focus. You can't assume that the rotational end stop is exactly infinity. You have to use the rangefinder if you want to be accurate.

Bob.

 

[Bryce]

Bob-
That is in keeping with the adapter being too thin. Basically, everything works fine except the infinity stop and the focusing scale.
Still, it represents an error in manufacture of the adapter. Whether or not it is significant probably depends on just how large the error is and which lens is in use. 12 and 15mm lenses could be a problem.

 

[Bob Parsons]

Now that I've thought about this again I think you're right, the distance of the lens flange from the camera bayonet is too small, ie the adapter is too thin. In the case of my 35/1.2 the lens flange must be too thin. I guess the real trouble with this is if the lens has floating elements whose relative positions depend on the focus distance. The floating corrections are only valid for one lens to camera flange distance. If an adapter or flange is too thin you will still be able to obtain infinity focus but the floating corrections could be wrong.

Bob.

 

[D&A]

Hi,

Thanks for all the replies. Like manual focus lenses of years ago (in the sixties and seventies)...most manufacturers would collimate their lenses precisely relative to their bodies and if one truned the focusing helical of these lenses to infinity (where the barrel could not rotate any more....the lens would be at perfect infinity. Leica M lenses are much the same. Put them on an M body and throw the lens to infinity and the rangefinder patch would be in perfect focus. If one looks at the current crop of Af 35mm lenses for SLR cameras..most all can fopcus past infinity. This is partially because the collimation is done by machine and no machine is precise enough to have precise infinity at the end of the barrel travel..so they overshoot it a bit.

Since Leica assumes their lenses will only be used on Leica bodies (like Nikon, Canon etc. assume much the same for their lenses/ bodies), Cosina realizes that their lenses may be used on all sorts of bodies and so leaves a little leeway or "overshoot of infinity to compensate for the various bodies. I suspect if a VC lens was used with any manufacturer adapter, the lens would still overshoot infinity by a small amount. Just a guess.

Dave

 

[D&A]

Hi,

I'm still trying to get a handle on using CV lenses with the M8 and how prevelent Cv lenses overshoot infinity on a properly calibrated M8. So far the few responses I've received in this post have found the same thing (that the CV lenses do overshoot infinity by a small margin). Before I decide to have the CV lenses looked at or recollimated...I was hoping to hear from some others who have various CV lenses (whether they use CV or Leica adapters or even CV "M" mount lenses) and a M8 and what they observe. Many thanks in advance.

Dave