How to test rangefinder on M6

[derphilipp]

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Hey,

 

during my last trip I got the feeling that the rangefinder of my M6 might be misaligned. How can I test that in a reliable way?

 

And if it is can I fix it on my own or do I need to find a repair shop?

 

best

 

Philipp

[Michael Geschlecht]

Hello Philipp,

 

Welcome to the Forum.

 

Here are a few suggestions you might try ON A TRIPOD.

 

1. Focus on the Moon on a clear nite & photograph it:

 

Re-focus & do this 2 more times & all together take 3 photos.

 

Does the Infinity mark on the lens agree with your focus thru the range/viewfinder each time you focus?

 

Are all of the photos of the Moon in focus?

 

2. Place a meter/yardstick on the ground so that it points away from you with your camera on a tripod set at 10 meters.

 

Move the camera on the tripod back & forth AS A UNIT, with you 10 meters away from the meter/yardstick, until the 2 rangefinder rectangles overlap precisely at the middle number on the meter/yardstick that is pointing away from you. 

 

Take a photo.

 

Now, without moving the tripod: Re-focus the camera to the middle number on the meter/yardstick 2 more times & all together take 3 pictures.

 

Is the middle number that you focused on the sharpest part of the photo? Does the re-focused mid-point read as 10 meters on the lens barrel?

 

Are the LIMITS OF ACCEPTABLE SHARPNESS approximately 1/3d of the distance in front of this mid-point number & approximately 2/3d's of the distance behind this same number?

 

You can tell this by reading the numbers on the meter/yardstick.

 

3. Do the same thing that you did in #2, just above, at 3 meters.

 

4. Do the same thing that you did in #2, just above, at 1 meter.

 

Then get back to us & tell us what happened.

 

Best Regards,

 

Michael

[spydrxx]

If you do a search under a term like "rangefinder adjustment" you'll get lots of ifo. FWIW, when I owned an M6, after years of owning an M4, I felt pretty confident doing the adjustment (as I still do on my Barnacks and M2, if needed, currently. I don't attempt anything with the roller cam however, leaving that to the pros. As far as testing, it is pretty easy...the things I look for are twofold: namely, do the images perfectly coincide at the appropriate distances (ie are they both horizontally and vertically aligned), and when aligned, does that match perfect focus at the film plane. First - find an object at infinity (although theoretically optical infinity is approx. 1000x the focal length of the lens) I usually use the moon or a bright star/planet. Next I measure from the film plane (mark on the camera body) to an object 4 ft away, and check the alignment. If both tests show the RF images coinciding, I'm happy. If not, I know I need to make minute adjustments with the vertical and/or horizontal adjustment screws. Once done I wanr to check the film plane. With the camera on a tripod, I open the rear flap and rubberband it up. I next place a fine ground glass (I actually use an old Nikon matte focusing screen) which I've placed and secured tightly over the film rails. Set the aperture to its widest, and with a locking cable release and the shutter set for bulb, open it up. I measure from the film plane mark to an image and focus on the image using the rangefinder, then inspect the image at the film plane with a 10-20x loupe. Focus should be right on the button....if not I usually know that means the lens or camera body needs the light touch of professional hands. The entire process for me takes about 2-3 minutes. I finally built a simple jig so I can use it to test alignment on a variety of my rengefinder bodies as well as my TLR bodies, using a 6ft. piece of wood (bar), a sliding stage to hold the camera, and a fixed point to focus on (the tip pf a chopstick). I routinely check for focus alignment about once/year due to the wide temperature variations where I live....more often than not I find that I need to get my eyeglasses checked.