Yashica MAT twin lens focus verification

[Sayan Mukherjee]

I saw a discussion thread to verify the focii of a TLR between the viewing and taking lenses. People advised using a wax paper on the film plane with shutter in Bulb mode.

Question:
1. Can I get an accurate result if I use a new tracing paper sheet?
2. What should I use as the subject to do the verification? Can I use a strong light bulb or a high contrast indoor layout (like a white wall with dark coloured furniture in front). The distance from camera to subject will not be more than 10-15 feet.

The camera in this case is a 45 year old Yashica MAT LM (the LM stopped working 20 years back!). The camera has just been serviced. But I have never suspected the lenses to have become different in focussing. I am apprehensive that the photos may be off focus when I get the prints!

 

[Jim Noel]

1. Yes
2. what you suggest will work. A wel lit sheet of newspaper will give you even more critical results.

 

[ic-racer]

I use a microscope slide with semi-transparent tape on it. I use an 'infinity' scene. I double-check it with film by 'bracket focusing' a few frames on an infinity scene with the lens wide open.

 

[John Koehrer]

It should be checked at infinity. Tracing paper, waxed paper and the slide with tape will all work.
The glass slide w/tape might be the easiest to handle.
The reason it's checked at infinity rather than close focus is if it's on at close distance it doesn't mean it's on at infinity. There are no separate adjustments for near & far.

 

[Jim Jones]

. . . Question:
1. Can I get an accurate result if I use a new tracing paper sheet? . . . /QUOTE]

Yes, if you can keep the tracing paper absolutely flat. However, I can't imagine this happening. A very flat piece of glass or other transparent material with semi-transparent tape may be the quickest solution. I've used plexiglass abraded with fine sandpaper and ground glass cut to size.

 

[jochen]

Hello,
the method of Jim Jones is the best. I take a cover glas of a 6x6 slide cut to size. It has to be placed exactly on the film guiding rails. Onto the front side toward the lens I make some marks or dots with a black Edding. The shutter is opened at B with a fixable cable release, aperture fully open. I take an infinity target (antenna or pylon) at least 500 mtr away. The focus is checked with a very strong loupe (10 - 20 x or a reversed strong wide angle lens). The image of the black marks has to be sharp together with the infinity target. Of course the camera has to be fixed on a table or tripod.