Rangefinder Calibration How-to

[Mrfrst]

Hey all,

My Canonet QL19 GIII had a rangefinder that was out of whack, and after some research and a couple false starts, I found a good way to get a pretty good calibration at home with equipment that most people will have on-hand, and I made a video showing how to do it (see below). I first calibrated it based on the distance scale on the focusing collar, but the first test roll showed that this was a poor approach since the distance scale itself was wrong, and the lens actually focuses past infinity at the infinity mark. The thing that worked was putting a ground-glass equivalent (frosted scotch tape) across the focus plane and aligning the rangefinder based on that. Seeing a video for the process would have saved me a lot of time, so I put one together to hopefully save somebody that trial and error process.

Enjoy!

 

[Eric Rose]

Thanks for the video. I have a little ground glass I use for this purpose to check my Leica's. It seems if I look at them the wrong way they go out lol.

 

[AgX]

The thing that worked was putting a ground-glass equivalent (frosted scotch tape) across the focus plane and aligning the rangefinder based on that.

Using the aerial image instead would even gain more resolution (if necessary).

 

[Mrfrst]

Aerial image? I'm not familiar with what the the term in this context... Could you fill me in?

Update: Some careful googling brought me to this: http://www.largeformatphotography.info/forum/showthread.php?45251-aerial-focusing

Cool concept, will keep in mind.

 

[AgX]

At the focal plane of a lens is

-) a "true" image if you catch it either with a ground glass or a matte, reflective screen

-) a virtual, "aerial" image that can be caught by another lens that focuses at that plane