Mamiya Sekor 500/5.6 not focussing to infinity

[simato73]

Simone, do you have any friends or second hand camera shop contacts that might loan you another Mamiya Sekor lens to check your adapters? 

I am thinking that another lens nearer the focal length of your problem lens rather than 45mm might be in order.  Just a thought.  Good luck.

Unfortunately that is not an option. Thanks for the suggestion though.

[simato73]

My thought is that the front group is to far away, so as to make the lens near-sighted. The other option is that the focus group doesn't move as freely as it should, i.e. the focus group can't travel far enough toward the film/sensor plane. Is there a way to adjust the travel of the focus group? The lens should focus slightly past the infinity mark.

Yes, the lens is a bit near-sigted. Boh reasons you offered are possible.
I suspect checking the travel of the focus group is possible but, as easy as it might be in this simple design, I am not confident opening up the focusing helicoid.

[simato73]

Following up from a few days ago.
Today I could finally do an infinity test (time and light were conducive).
I've chosen the Sun as a test object (using an Astro-Baader filter).
The following images were obtained after focusing all the way to infinity.
The first is f/5.6, then f/8, f/11, f/16, f/22 and f/32. All images are 100% crops from OOC JPEGs.
The last shows the adapters, a Mamyia/Nikon plus a Nikon/Fuji.
(the Nikon/Fuji is from Kipon and is MUCH better machined than the other one I have, from Metabones, which budges a lot in all dimensions).

The images clearly show that infinity focus is not achieved and that the images become better stopping down just because of increased DOF (actually the images at f/5.6 are quite soft even when properly focused but this is not evident here)

[Mongo]

In Mongo's view, the test tell you some critical distances (albeit tiny) are not quite right and that the lens is capable of infinity focus if you can correct those distances.

As a very simple further test, Mongo still think you should try this:-

"one quick thought. When you get an opportunity, mount the lens with adaptor onto the camera. Set it to infinity as much as possibly. Then, while looking through the viewfinder, unscrew the front element group slightly (as if you were going to remove it). Does this make the infinity focus better or worse "

[simato73]

In Mongo's view, the test tell you some critical distances (albeit tiny) are not quite right and that the lens is capable of infinity focus if you can correct those distances.

As a very simple further test, Mongo still think you should try this:-

"one quick thought. When you get an opportunity, mount the lens with adaptor onto the camera. Set it to infinity as much as possibly. Then, while looking through the viewfinder, unscrew the front element group slightly (as if you were going to remove it). Does this make the infinity focus better or worse "

That is something worth trying, when I get the opportunity.
I suspect that unscrewing the front element will make the focus problem worse (the lens is shortest at infinity)

[Bjørn Rørslett]

Maybe, maybe not. The air spaces in the optical design are important and changing them alters the lens configuration. Worth a try.

[Hugh_3170]

Simone, please forgive me if you have already done something similar to this:  one thing that is easy to try out is to set the lens on infinity and photograph a repeating pattern such as electricity supply poles or fence posts along a straight section of road. 

At some point out into the distance you will be able to estimate just where the sharpness of the image starts to fall off - you can then pace this out or measure it if you are fit & keen. 

If this distance is close in, then the excess thickness of your two adapers may be significant.  On the other hand if this distance is a long way out, then they may not need to be thinned down very much to obtain infinity focus.  The focus scale on the lens may be of some help here if it is finely graduated.  Either way, this process should give you a starting point to make adjustments.

[simato73]

Simone, please forgive me if you have already done something similar to this:  one thing that is easy to try out is to set the lens on infinity and photograph a repeating pattern such as electricity supply poles or fence posts along a straight section of road. 

At some point out into the distance you will be able to estimate just where the sharpness of the image starts to fall off - you can then pace this out or measure it if you are fit & keen. 

If this distance is close in, then the excess thickness of your two adapers may be significant.  On the other hand if this distance is a long way out, then they may not need to be thinned down very much to obtain infinity focus.  The focus scale on the lens may be of some help here if it is finely graduated.  Either way, this process should give you a starting point to make adjustments.

Thanks for the suggestion; it may be a bit difficult to find a suitable place as you recommend.
Most of all I know it is not a problem with the adapters. I have several and have tried all the combinations (albeit not as systematically as you suggested) and the results don't change.
Also, I have another lens in Mamyia mount, which I use with the same adapters, and it does not have the infinity problems this one shows.

[Hugh_3170]

OK, if the adapters are proven to be all right,   then it seems as if the lens needs a technician to adjust the end stop for the infinity focus. 

On the other hand, the test as outlined should still give you an indication of whether the lens is just a little bit off at its infinity setting or is a long way off.  Good luck - these things can be frustrating.