Repair Guide / Rangefinder
Rangefinder Alignment
Adjusting horizontal and vertical rangefinder alignment on Leica M cameras. What causes misalignment, how to test for it, and how to correct it.
Overview
Rangefinder alignment is the adjustment that ensures the rangefinder patch in the viewfinder accurately indicates focus. When the rangefinder is correctly aligned, the two images in the patch coincide when the lens is focused at the distance shown on the focus scale.
Misalignment can happen gradually over time as the camera is used, or suddenly after a drop. Horizontal misalignment is more common and more noticeable -- the rangefinder patch images don't coincide horizontally. Vertical misalignment is less common but causes the images to be offset vertically.
On Leica M cameras, horizontal alignment is adjusted via a screw accessible through the front of the camera, near the rangefinder window. Vertical alignment requires removing the top plate to access the adjustment mechanism.
I check rangefinder alignment on every Leica M I service. It's the last step of a CLA, done after everything else is back together and the shutter speeds are verified.
Tools needed
Procedure
Set up test targets
Place a target with fine detail at 1 meter, 3 meters, and as far as possible (infinity, or at least 30 meters). A piece of newspaper taped to a wall works well. You need targets at multiple distances to verify alignment across the focus range.
Test horizontal alignment at 1 meter
Mount a 50mm lens. Focus the lens at 1 meter using the focus scale. Look through the viewfinder at the 1-meter target. The two images in the rangefinder patch should coincide horizontally. If they don't, note which direction they're offset.
Test at 3 meters and infinity
Repeat the test at 3 meters and infinity. If the alignment is correct at 1 meter but off at infinity, or vice versa, there may be a cam issue rather than a simple alignment problem. Alignment adjustment affects all distances equally.
Locate the horizontal adjustment screw
On Leica M cameras, the horizontal adjustment screw is located on the front of the camera, near the rangefinder window. It's usually covered by a small brass plug that must be removed with a lens spanner. The screw underneath is a fine-thread adjustment.
Adjust horizontal alignment
Turn the adjustment screw in small increments -- no more than 1/8 turn at a time. Check the alignment after each adjustment. The direction of correction depends on the camera model. On most Leica M cameras, turning the screw clockwise moves the patch to the right.
Verify across all distances
After adjusting, verify alignment at 1 meter, 3 meters, and infinity. The alignment should be consistent across all distances. If it's not, the issue may be with the rangefinder cam or the lens itself.
Check vertical alignment
Vertical misalignment is less common. If the images in the patch are offset vertically, the vertical adjustment requires removing the top plate. This is a more involved procedure -- consult a service manual for your specific camera model.
Shoot a test roll
After aligning the rangefinder, shoot a test roll with the lens wide open at close distances. Check the focus accuracy on the developed film. The rangefinder should be accurate to within the depth of field at the aperture used.
Warnings
Do not over-adjust. Small movements of the adjustment screw cause significant changes in alignment. Work in small increments.
Vertical adjustment requires removing the top plate. If you're not comfortable with this, have a technician do it.
Rangefinder alignment is lens-specific to some degree. A rangefinder that's accurate with one lens may be slightly off with another. Align for the lens you use most.
If the rangefinder patch is dim or has a ghost image, the beam splitter may need cleaning or replacement. Alignment adjustment won't fix a dim patch.
Notes
I align rangefinders at 1 meter because that's where the depth of field is shallowest and errors are most visible. If the alignment is correct at 1 meter, it's usually correct everywhere.
The rangefinder in a Leica M is a precision optical instrument. It can drift out of alignment slowly over years of use. I check alignment on every Leica I service, even if the previous owner says it's accurate.
In Florida, I've found that cameras stored in humid conditions sometimes have rangefinder patches that are dim due to moisture condensation on the beam splitter. Cleaning the beam splitter often restores brightness without requiring alignment adjustment.
If you're not getting accurate focus even after alignment, check the lens. A lens with a worn or loose helicoid can cause focus errors that look like rangefinder misalignment.
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