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Checking rangefinder adjustment on film M


rirakuma

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Hi guys I just wanted to ask if this is the correct way to check rf accuracy on my film M. I'm leaving on a trip soon and I want to see if my lens is calibrated correctly on the film body (I'm pretty sure its close focusing). I'm going to mount the lens on an M240 in live view mode then focus to an object. I will then place the MP at the exact location (mounted on a tripod) with the same lens at the same focus distance. If the RF is not spot on, is it safe to assume that wherever the patch sits is how much I need to compensate for the correct focus point?

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Put your camera on a tripod, open the back and place a piece of fine ground glass flat across the focal plane. Open your shutter with a cable release, aperture on your lens wide open. I usually check both infinity focus and focus about 6 ft on my bodies. Using the rangefinder, focus on the desired object. For near objects measure the actual distance from the point of focus to the film plane. Visually check to see if it corresponds to the distance scale on the lens. Now with a loupe check the ground glass...is focus perfect. If so, you're all set. Takes less than 10 minutes to set up and check. If focus isn't perfect, your rf is out of adjustment.

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Thanks for the replies guys :). Do you mean the ground glass like they have on the Hasselblad finders? Luckily I do have one of those but I don't think it will fit where the film sits. I don't mean to sound receptive but is it not possible to check it by comparing focus using live view with the M240?

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Thanks for the replies guys :). Do you mean the ground glass like they have on the Hasselblad finders? Luckily I do have one of those but I don't think it will fit where the film sits. I don't mean to sound receptive but is it not possible to check it by comparing focus using live view with the M240?

Yes - have done this to compare my 6 film Ms to my digital. Be sure to use a solid, firmly positioned tripod. The tripod mount positions are different on the digital M, so there will be a horizontal shift to the film M, unless you use a focusing rail system to shift it. Be sure the "film plane" is in as close to the same position as possible.

Focus on the digital, ideally so the lens is directly on an index mark (or mark with a pencil). Then mount the film M with the lens on the same mark, and check the rangefinder.

No, it's not perfect, but will be close. Film has a bit more leeway anyway.

Edited by TomB_tx
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Thanks Tom! Its good to know that I can at least get a rough idea on accuracy. Luckily I got an email from Leica Ginza and they offer a one hour calibration service at a very reasonable price so I'll do that a few days after my arrival. Thanks everyone for the help :)!

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 I don't mean to sound receptive but is it not possible to check it by comparing focus using live view with the M240?

 

I don't see how this is possible to do accurately. The centre of the tripod socket to the face of the lens flange on the M240 is approximately 20mm, on a film M it is approximately 16mm, so you would need a way to very very accurately move the tripod 4mm so the datum point of the lens flange is in the same position (using the lens flange because there is no film plain/sensor datum mark to work from). Tripod plates need to be exactly the same, and clamping them with exactly the same pressure, and keeping the camera body dead square to the subject, well, it's not going to happen is it?

 

Steve

Edited by 250swb
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I don't see how this is possible to do accurately. The centre of the tripod socket to the face of the lens flange on the M240 is approximately 20mm, on a film M it is approximately 16mm, so you would need a way to very very accurately move the tripod 4mm so the datum point of the lens flange is in the same position (using the lens flange because there is no film plain/sensor datum mark to work from). Tripod plates need to be exactly the same, and clamping them with exactly the same pressure, and keeping the camera body dead square to the subject, well, it's not going to happen is it?

 

Steve

 

The datum mark is on the hot shoe, its the small line indent that you see just before the edge (I hope that's correct). I don't expect to get pin point accuracy with this method but it's better than not knowing.

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It sounds like you found a good solution. Just to follow up about your question on ground glass. The ideal would be a flat piece which just fits the film rails. For years I used a piece of matte Scotch tape mounted on a microscope slide. Clumsy but it worked fine. A couple of years ago I ended up with a spare fine matte focusing screen from a Nikon F3, which, with a little wiggling fit just fine and have used that ever since.

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The datum mark is on the hot shoe, its the small line indent that you see just before the edge (I hope that's correct). I don't expect to get pin point accuracy with this method but it's better than not knowing.

 

There's no film plane/focal plane mark on my MP?

 

Steve

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I used to use a spare matte focusing screen off a Nikon FM2n taped to the film rails.   Checking by shooting film is great for just checking, but it's impractical for making adjustments, even if you develop your own film it would turn a few minutes' inexpensive job into a multi-hour expensive one.

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