Rangefinder Ground Glass Test

jwolf

jwolf

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Photos:https://www.rangefinderforum.com/rffgallery/showcollection.php?cid=10931

I thought I would test the focus accuracy of my lenses before I run some film. I imagine you all have passed this general process around before, but I thought I would share my process. I had an old Canon 1D film camera focusing screen handy. I am not sure if the metal framed Nikon screens will work. Anyway, this was easy to tape flat with painters tape, important to do it frosted glass toward the lens. Luckily, I have an old Schneider 8x lupe. A 4x is not enough to really see the focus plane. I focused on an object with the rangefinder (back open with the ground glass exposed), tripped the shutter with Bulb and kept the shutter open, now sight the ground glass with the loupe. It would be best with 3 hands, but you can do it with 2. Works best seated so you can keep you distance consistent from the focusing to the testing with the loupe. I imagine you could test different distances etc. I tested a portrait distance of 8 feet with the Canon 50mm 1.4. Hope this helps someone. Obviously, every lens has it's on ability to be off. I noticed the Canon 100mm f2 has a little tab that seems adjustable. Hope this helps someone.
 
You've got the process right. As you note, an unframed screen is necessary; I use an Olympus OM series focus screen for this (because I have one, and its perfect for it). The frosted surface should lay against the inner film rails, and inside the outer (slightly higher) guide rails [just as pictured]. Best used with a tripod to keep the camera and position steady.
 
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Film thickness needs to be accounted for. When first M8 came out focus was off. I knew what was wrong, but evidently Leica engineers did not.
 
Thanks for the reminder, I do it with a 6x6 focus screen on my folders. With 35mm the screen is so small the focus area is muy chiquito, but I still do it.
 
I've tested the focusing in the same manner as noted above...I also mount the camera on a tripod, make sure its level, both ways and as square to my subject as possible...I have seen the focusing target on ebay and I am tempted to buy one...for now I use a big cereal box with large and small graphics on it.
My focusing screen came out of an Olympus OM-2n and is a split screen...
 
jwolf said:
Photos:https://www.rangefinderforum.com/rffgallery/showcollection.php?cid=10931

I thought I would test the focus accuracy of my lenses before I run some film. I imagine you all have passed this general process around before, but I thought I would share my process. I had an old Canon 1D film camera focusing screen handy. I am not sure if the metal framed Nikon screens will work. Anyway, this was easy to tape flat with painters tape, important to do it frosted glass toward the lens. Luckily, I have an old Schneider 8x lupe. A 4x is not enough to really see the focus plane. I focused on an object with the rangefinder (back open with the ground glass exposed), tripped the shutter with Bulb and kept the shutter open, now sight the ground glass with the loupe. It would be best with 3 hands, but you can do it with 2. Works best seated so you can keep you distance consistent from the focusing to the testing with the loupe. I imagine you could test different distances etc. I tested a portrait distance of 8 feet with the Canon 50mm 1.4. Hope this helps someone. Obviously, every lens has it's on ability to be off. I noticed the Canon 100mm f2 has a little tab that seems adjustable. Hope this helps someone.
Click to expand...

You've got the screen resting on the inner rails, right? In one of the pics, it looked like it was resting on the "black" part of the film gate.

Dante
 
Ronald M said:
Film thickness needs to be accounted for. When first M8 came out focus was off. I knew what was wrong, but evidently Leica engineers did not.
Click to expand...

We’re not discussing digital sensors here, nor the optical thickness of a digital array.
This is about focus testing in a film camera. Film substrate thickness is never a factor, as the film thickness lays behind the image plane. Film emulsion thickness may possibly play a part in image sharpness (in color films in particular) but differences in sharpness are generally considered to be a factor of grain character rather then emulsion thickness. These are moot issues in this discussion because we’re talking about testing focus at a ground glass surface, in the same position as the emulsion surface. Neither Emulsion thickness nor Film thickness are germane here.
 
Ronald M said:
Film thickness needs to be accounted for. When first M8 came out focus was off. I knew what was wrong, but evidently Leica engineers did not.
Click to expand...

Since the emulsion is on the front of the film, it should be on the same plane as the frosting on a screen. That's how I envision it.


Yeah, a tripod would have been the smart thing to do. : )


Dante, it was sitting flat, but may have looked a little off.
 
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