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4 minutes ago, farnz said:

You could try placing your camera at an angle to the fret board with the guitar horizontal and focussing on one of the central strings with the aperture wide open.  If one of the other strings turns out to be in focus then you'll be able to confirm whether it's front or back focussing and roughly by how much.

Pete.

If only I’d thought of this before finishing a film and sending it off to the lab 

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Late to this discussion... but a couple of points...

The 35 Summicron ASPH has been known,  for some samples, to exhibit mild focus shift.  Mine does this when stopping down to f2.8 and f4, but recovers at f5.6 (a long time ago Sean Reid reported the same behavior with his).  This is easily accommodated with shooting technique, and isn’t an issue with my print results.  FWIW, the 35 Summarit exhibits no focus shift (and has less tendency to flare than the Summicron ASPH).

Some here mentioned checking calibration with a digital camera.  While digital tolerances are narrower than with film, the real assistance comes from using an M with live view, like the M240 or M10.  Focusing with live view at an appropriate target (on a tripod of course), one sees exactly what the camera sees, as it’s focusing off the sensor.  One can then easily check to see if focusing by the RF produces identical results.  If only one lens is off, and others are not, one can deduce the culprit.

Leica service can of course check everything; they’ll want body and lens(es) to avoid confusion. 

Jeff

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8 hours ago, Exodies said:

The rangefinder isn’t focussing directly it’s aligning two images at the distance which will be in focus. Objects in the rangefinder patch at a different distance will not be overlapped.

Ah, yes now that makes sense. I’ve forgotten about that. 

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If you indeed have focus shift, you need to determine at what aperture it exists as well as how much distance the shift represents. Since you're using a film camera, you will need to sacrifice a roll of film to make that determination. Essentially you would put your camera on a tripod, use a ruler, tri-square, or scale like the one below, and take a series of shots focusing on a zero mark starting with your lens wide open and each subsequent shot closing the diaphragm by 1 f/stop. Whatever scale you use should be lined up so the dark black line is horizontally level with the center or your lens and angled 45 degrees vertically away from the lens. You can find the test chart here but you may need to try one or two different viewers to get it to show properly. You can then print it out with the instructions. http://www.kscameraclub.org/docs/pdfs/focus_test_chart_edited.pdf

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To continue - once you've identified the aperture at which focus shift occurs, you can do one of several things....easiest is to avoid using that aperture for close work (DOF can usually bail you out at greater than close distances) , or when focusing with the rangefinder, focus on a spot on your subject compensating for the known amount of focus shift.

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13 minutes ago, spydrxx said:

To continue - once you've identified the aperture at which focus shift occurs, you can do one of several things....easiest is to avoid using that aperture for close work (DOF can usually bail you out at greater than close distances) , or when focusing with the rangefinder, focus on a spot on your subject compensating for the known amount of focus shift.

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I'd check focus with a few lenses.  If they're all off, its the camera

A friend of mine had his RF go off just by tossing it on a bed

I'd send the camera in to have it checked by a pro & adjusted if need be

It happens

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