How to know my M3’s rangefinder works correctly?

[shaozhuohong]

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I bought an old M3. But how to know my M3’s rangefinder works correctly? I mean if my lens’s meter say 2-meter, but the rangefinder’s meter say 2.1-meter.

 

If I set the lens’s meter to “infinity distance”, at the same time, two images coincide perfectly in the viewinder. Does this mean my M3’s rangefinder works correctly?

 

Thank you for your help!

[doubice]

.........If I set the lens’s meter to “infinity distance”, at the same time, two images coincide perfectly in the viewinder. Does this mean my M3’s rangefinder works correctly?

 

Thank you for your help!

 

If the images coincide at infinity when the lens is set to infinity, theoretically the rangefinder should be fine, unless it is seriously out of alignment. The M rangefinder has about three adjustment points (IIRC) - infinity, mid range and close range.

 

Why don't you buy a cheap roll of film, set the camera on a tripod and shoot some tests at varying distances - focus using the rangefinder (forget the distance scale). Leave the lens at its largest aperture (fully open) so that you have as shallow a depth of field as possible.

 

A 24 exposure negative film will not cost you more than $20.00 to process and print - that is the cheapest diagnostic process you will find anywhere. The M3 has just about the best rangefinder system of any 35mm camera ever made.

 

Good luck,

 

Jan

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[Michael Hiles]

Jan's advice is right. If your pictures are sharp where you focused, your M3's rangefnder is OK. Do the simple test.

[Finnkare]

I think Barry Thornton was using a sheet of white paper/cardboard with vertical lines marked on it to test the focusing accuracy. He placed it into various distances from the camera, non-parallel to the body and shot a couple of pictures always focused on the middle line.

[christer]

I use the following device to test rangefinder accuracy. As can be guessed from the shadow, the area with the number is inclined 45°. The "real" distances between the horizontal lines are 1,4 cm and the distances between them as the camera sees it is 1,0 cm.

 

The vertical lines are used for focusing. Focusing at a distance of 2 meters (and above!) is not easy. A hint that may be useful is to focus so that the top and the bottom of the vertical lines as seen in the rangefinder window are equally out of focus.

 

Use the largest aperture of your lens as it is otherwise difficult to make a judgement. Use ISO 100 speed film as grain will otherwise be a hindrance for your judgement as you will need to enlarge quite a lot to see enough. And use a tripod. Have the camera at the same height as your eye when you stand upright and have the test image at the same height.

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[christer]

The picture above was made with a 90mm Elmarit-M 1:2,8/90mm opened up/closed down to f/8,0.

 

The picture below was made with the same lens fully open. I have no idea if the lens "front focuses" or not, or if I myself "front focus".

 

Anyway it is interesting to see the effect of using the lens at f/2,8 compared to using it at F/8,0

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[dkCambridgeshire]

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With the camera on a tripod and with the back open, if a piece of translucent drafting film or translucent tracing paper is secured across the film gate rails, the image in the film plane can be seen and compared to the focused viewfinder image. Both images should be in focus. If not, the rangefinder needs adjusting. The drafting film can be secured with a couple of pieces of sticky tape.

 

Cheers

 

dunk

[Guest mc_k]

...I have no idea if the lens "front focuses" or not, or if I myself "front focus"...

 

how far was the target?

[tobey bilek]

There are two adjustment points, infinity and one meter from the film plane.

 

Infinity is not 100 yards, it is a star at night.

 

There is a vertical adj, but unless it is radically off, will not a bearing on focus, just user annoyance.

 

The material at the focus plane is not correct as the RF is adjusted to where film actually lies in practice, not the theoretical . The film channel has debth and film curves. This explains why digi M`s have focus issues. Their sensor plane and theoretical location are exact. To be sure, it does make a difference.

Edited December 9, 2009 by tobey bilek

[christer]

With the camera on a tripod and with the back open, if a piece of translucent drafting film or translucent tracing paper is secured across the film gate rails, the image in the film plane can be seen and compared to the focused viewfinder image. Both images should be in focus. If not, the rangefinder needs adjusting. The drafting film can be secured with a couple of pieces of sticky tape.

 

Cheers

 

dunk

 

Sounds good. Wonderful in theory. But does not work for me in practice.

 

You need a lot of light on the subject if you want to focus extremely accurately with the rangefinder. You need darkness to check focusing on the film plane whether it is translucent drafting film or translucent tracing paper. Can be solved by using a large thick black cloth over your head and the camera - but not over the lens.

 

And the back door of the camera needs to be fixed in an open position as it will otherwise fall down and block your view. More sticky tape, or should one use a string? Or place camera vertically?

 

You need to put the tracing paper (or whatever you use) exactly where the film plane is. We need to be very accurate, we are talking about tenths of millimeter. This is difficult.

 

You need to make judgements based on what you see on a 24x36mm piece of tracing paper, and that probably when you are standing up. I have difficulties making a judgemen when looking at a negative using a 10x aspheric loupe. And then I am sitting at a desk with the negative on a light box.

 

In summary, it did not work for me. But all men were not created equal. At least not in every sense.

[christer]

how far was the target?

 

The target was 2 meters away.

 

I tested 3 lenses; 35mm, 50mm and 90mm using the same distances in all cases. I tested at 1 meter and at 2 meter. I tested with the lenses wide open and also with the lenses closed down three stops. (However, when I did resolution tests some time ago I tested at 40x the focal length because the test chart was designed to give a direct read-out of lpms if the factor 40 was used. Additionally this facilitated the comparison of different lenses/focal lengths with the test image always being the same size on the negative.)

 

If you want to test yourself, you may wish to consider the following: make subseries of five shots (fit nicely in negative carrier) with the first shot being of a piece of paper with details as follows:

 

M7 chrome body

50mm

1 meter

f/5,6

 

Make two shots at each f-stop tested, focusing each separately. Shoot twice with lens fully open and twice with lens stopped down. That makes five negatives. I have a flat bed scanner that scans five negatives at a time. It saves a lot of time and energy when reviewing the result if one has the data available together with the negatives

[dkCambridgeshire]

Sounds good. Wonderful in theory. But does not work for me in practice.

 

You need a lot of light on the subject if you want to focus extremely accurately with the rangefinder. You need darkness to check focusing on the film plane whether it is translucent drafting film or translucent tracing paper. Can be solved by using a large thick black cloth over your head and the camera - but not over the lens.

 

And the back door of the camera needs to be fixed in an open position as it will otherwise fall down and block your view. More sticky tape, or should one use a string? Or place camera vertically?

 

You need to put the tracing paper (or whatever you use) exactly where the film plane is. We need to be very accurate, we are talking about tenths of millimeter. This is difficult.

 

You need to make judgements based on what you see on a 24x36mm piece of tracing paper, and that probably when you are standing up. I have difficulties making a judgemen when looking at a negative using a 10x aspheric loupe. And then I am sitting at a desk with the negative on a light box.

 

In summary, it did not work for me. But all men were not created equal. At least not in every sense.

 

I have tried it with my M6 in my kitchen using a loupe to view the image and it worked ok. I have only used it to test the close focus ... have not tried it at infinity. There were no problems with the back door or securing the drafting film.

 

Cheers

 

dunk

[normclarke]

I have seen a simple test whereby a pencil line equal to the r/f baseline is marked with a plus at one node and a cross at the other. The mensuration must be very accurate. Simply observe through the eyepiece at about 1 mtr from the chart that when the lens is at infinity the cross and plus will merge. I understand the lens makers consider infinity to be 1000X f/l of the lens in question.

 

Best,

 

normclarke.

[christer]

I have tried it with my M6 in my kitchen using a loupe to view the image and it worked ok. I have only used it to test the close focus ... have not tried it at infinity. There were no problems with the back door or securing the drafting film.

 

Cheers

 

dunk

 

Your dexterity ist obviously much better than mine; I can't even use chop sticks.

[christer]

I have seen a simple test whereby a pencil line equal to the r/f baseline is marked with a plus at one node and a cross at the other. The mensuration must be very accurate. Simply observe through the eyepiece at about 1 mtr from the chart that when the lens is at infinity the cross and plus will merge. I understand the lens makers consider infinity to be 1000X f/l of the lens in question.

 

Best,

 

normclarke.

 

Interesting. I had to try it out at once.

 

With the camera placed on a tripod with exactly 100 cm between target and film plane, the distance between two thin vertical lines coinciding with the left and right hand sides of the small rangefinder window was 77,5mm. The camera was on level with the target, and film plane and target were parallel.

 

With the distance set to infinity the two lines did not coincide. A third line drawn on the target where the right line appeared with the distance set to infinity was 7,5 mm from the left line. To get the lines to coincide it would have been necessary to turn the distance setting beyond infinity.

 

I tested two bodies and three lenses. A six results were the same which I found reassuring.

[normclarke]

The centres for the .72 mag finders are 68.5mm.

 

Best,

 

normclarke.

[christer]

The centres for the .72 mag finders are 68.5mm.

 

Best,

 

normclarke.

 

I have japanese viewfinder magnifiers on my cameras which I should probably remove and then redo the test.

 

Thanks for your input