Which is the problem: rangefinder or lens?

[dyao]

I noticed today that my Biogon 35/2 won't focus to infinity, however my Canon 50/1.8 will. I'm using a M4-2, and it's my only M body. I tried the Canon with both a cheapo LTM-M adapter and a Voigtlander LTM-M adapter.

If you had to bet money, would you bet on the rangefinder or the Biogon as being out of whack? If it was the Biogon, would it be an easy fix?

 

[dyao]

I just remembered that I have an old Industar-50 - I tried it out and it actually focuses a little past infinity! go figure.

 

[Robert Lai]

Can't tell which is off without doing some testing on film. Shoot the lenses with "infinity" based on the RF. Then shoot them at their infinity stops on the focus ring. I realize that your Biogon may not get to infinity on the RF, so just shoot it on the focus stop. Take notes as to what setting was used for each frame.

After you get the film developed, it will tell you which lenses have the infinity stop set properly, and if your RF is indicating infinity correctly. If you have a scanner, you could scan the film and pixel peep, or else use slide film and a projector. You'll then know which way to go with each lens or the camera.

 

[dyao]

Thanks for the advice Robert. I'll shoot a few test slides next time I get a roll developed.

I tried the mirror test and the 50mm 1.8 is on the money - when I'm 4 feet away it focuses at 8 feet, etc.

However the Biogon is a tad to the right - when I'm at 2.5 feet it's just a hair past 5 feet, when I'm at 1 meter it's just a hair past 2 meters. So without running any film tests, I think it may be the Biogon...

 

[dyao]

Well I did the test properly just now with a piece of black tape, and it's actually my Canon 50/1.8 that is misfocusing. When I do the mirror test, I set the lens to 4 feet, move the camera body until tape is in focus, then focus on my reflection, and it ends up a little shy of 8 feet. So...

The Biogon is dead-on at 2.5 feet and 1 meter, but can't focus the rangefinder to infinity.

The Canon is a little inaccurate at short distances, but can focus to infinity.

If I adjust the M4-2's rangefinder to let the Biogon focus to infinity, will that ruin the Biogon's close-focusing ability? I will probably have the Canon looked at.

 

[ferider]

Remember, the Biogon has a hyperfocal distance of 20m at f2. Everything beyond will always be sharp. The Canon's hyperfocal distance at f1.8 is 47m. So it's much more sensitive.

Also, type II CV and Leica adapters are a tiny bit thicker than most generic and CV type I adapters.

If or not the Canon needs to be looked at depends what you mean by off at infinity (how much). Also use a star at night to do the infinity test.

Roland.

 

[dyao]

Remember, the Biogon has a hyperfocal distance of 20m at f2. Everything beyond will always be sharp. The Canon's hyperfocal distance at f1.8 is 47m. So it's much more sensitive.

Also, type II CV and Leica adapters are a tiny bit thicker than most generic and CV type I adapters.

If or not the Canon needs to be looked at depends what you mean by off at infinity (how much). Also use a star at night to do the infinity test.

Roland.

Thanks for the help Roland. Yes, I did do the test at night using the moon. I suppose if the Biogon is accurate at close distances, that's all that matters, as I don't tend to use it as a landscape lens and as you mentioned the hyperfocal distance is relatively short. It just bothers me that the Biogon can focus close distances accurately but cannot focus my finder to infinity.

 

[35mmdelux]

Its probably the lens since your other lens focus ok.

 

[dyao]

Sorry, when I say 8-10% of the rangefinder box, I mean the distance between the two split images is 8-10% of the width of the rangefinder box. That seems like a lot to me.

 

[35mmdelux]

I wouldnt say that all of HCB fotos are tack sharp.