I am not sure if this question has come up before, if yes pls let me know the link.

I would like to check on my focusing accuracy on my M6, especially on close up.

First question:

I have checked my M6 with various lens set at infinity. The image are all in-line thru the view finder. My I correct to say that the focusing mechanism on my M6 is being calibrated or correctly adjusted.

Second question:

I have done some close up shot with newspaper ( around 3 ft with wide open lens - 75mm at f1.4 ). My shot was angled slightly to test out the DOF as well. I found out that the focused point was slightly ( about 1 inch ) in front of what I focused. Is this normal? Or I need to send my M6 for adjustment, or can that be done?

-- Marc (leica_image@yahoo.com), March 18, 2002

Answers

Marc: Which version of the M6 are using, .58, .72 or .85?

The rangefinder can be correct at infinity, but off up close. You are correct in checking it at both ends of the spectrum.

I check my rangefinder with a yard stick and photograph at 45 degrees. I mark where I am shooting and refocus between frames. The .85 would be the most accurate of the three. If the frames are still off, and the camera is under warranty, I would get it repaired.

-- Mark A. Johnson (logical1@catholic.org), March 18, 2002.

It is a classic M6 - 10 years old already with view finder .72. Do you mean it should be dead accurate even at close range?

-- Marc (lecia_image@yahoo.com), March 18, 2002.

Yes.

-- Mark A. Johnson (logical1@catholic.org), March 18, 2002.

Yes it should be spot on at close up as well. If you haven't tried it yet, try doing your close-up testing while the camera is on a tripod. It is surprising how much ones head moves around without one realising.

-- sait (akkirman@clear.net.nz), March 18, 2002.

I think the viewfinder magnifier 1.25X Art. No. 12004 is an necessity for 75mm.

I also have a 75mm Summilux. With M6/0.85 plus the magnifier, it is like heaven!

-- Joe Lee (joelee@1388.com), March 19, 2002.

The issue of rangefinder accuracy is discussed very nicely in Gunther Osterloh's book on the M Leica, which I recommend strongly to anyone interested in technical aspects of M operation (including lightmetering, M lens design and construction, basic optical principles, etc.). It is the best discussion of a variety of M- related subjects that I have read.

As for RF accuracy, my understanding is that the absolute error of measurement is about 1/2 to 1 inch for at a distance of 10 feet (with the 0.72X VF, which was the only one in production when the book was written). This, of course, is independent of the lens, focal length, F-stop, etc. But it does depend on the VF magnification.

The error you site sounds a little high. I wonder if you are measuring it properly. Remember the distance is measured to the film plane. which is not quite at the back of the top plate. And there is a parallax error because the RF-VF is not at lens level. This is different from the parallax correction for the frame lines. I'm not an expert, but the discrepancy could be due to the way you are measuring distances.

-- Eliot (erosen@lij.edu), March 19, 2002.

Marc,

One trick for testing close-up rangefinder accuracy is to:

* stick a bit of black tape on a mirror

* set the lens distance to 5 feet

* posiiton yourself so that the black tape is in focus according to the rangefinder

* without moving the camera, re-focus on your camera's reflection in the mirror.

* The lens distance scale should then read 10 feet.

-- Ray Moth (ray_moth@yahoo.com), March 20, 2002.