Repair Guide / Shutter
Shutter Calibration
Testing and adjusting shutter speeds on cloth and metal focal plane shutters. What tools you need, what tolerances are acceptable, and when to stop.
Overview
Shutter calibration is the job I do at the end of every CLA. You clean and lubricate the camera, then you verify that the shutter is actually running at the speeds marked on the dial. Most unserviced cameras are slow at the fast speeds and erratic at the slow speeds.
The slow speeds -- 1/8, 1/4, 1/2, 1 second -- are governed by a separate mechanism from the fast speeds. The slow-speed governor is a small escapement mechanism that controls the timing. It runs on lubricant. When the lubricant dries out or becomes contaminated, the slow speeds run slow or stop working entirely.
The fast speeds -- 1/60 through 1/1000 or 1/2000 -- are controlled by the tension of the shutter curtains and the gap between them. Adjusting fast speeds requires changing the curtain tension or the gap, which is more involved than cleaning the slow-speed governor.
In Florida, I calibrate every camera I service. The humidity here can affect lubricant viscosity, which affects shutter timing. A camera that was accurate in a dry climate may run slow here.
Tools needed
Procedure
Test before touching
Before doing anything, test the shutter speeds with your tester. Record the readings at every speed. This tells you what you're dealing with and gives you a baseline to compare against after service.
Identify the problem
Slow speeds running slow almost always means the slow-speed governor needs cleaning. Fast speeds running slow usually means the shutter curtains need cleaning or the curtain tension needs adjustment. Inconsistent speeds at any setting usually mean contaminated shutter blades or curtains.
Access the slow-speed governor
On most cameras, the slow-speed governor is accessible from the bottom of the camera after removing the baseplate. On Leica M cameras, it's accessible from the front after removing the lens mount. Consult a service manual for your specific camera.
Clean the governor
Apply a small amount of naphtha to the governor with a cotton swab. Work it into the mechanism by cycling the shutter repeatedly. The naphtha will dissolve old lubricant and carry it away. Allow to dry completely.
Re-lubricate the governor
Apply a very small amount of Molykote DX to the governor pivot points. Less is more here. Too much lubricant will cause the slow speeds to run fast. Use a fine brush or a sharpened toothpick to apply the grease precisely.
Clean the shutter curtains or blades
If the fast speeds are slow or inconsistent, the curtains or blades may be contaminated. On cloth curtains, apply naphtha with a cotton swab and allow to dry. On metal blades, the same approach works. Never touch the curtains with your fingers.
Lubricate the shutter rails
The rails that the shutter curtains run on need a very thin coat of lubricant. I use Tribolube on a fine brush, applied sparingly. Too much lubricant on the rails will migrate onto the curtains.
Test and adjust
After cleaning and lubricating, test the shutter speeds again. Compare to your baseline. The slow speeds should be within 30% of the marked speed. The fast speeds should be within 20%. If they're not, further adjustment is needed.
Adjust curtain tension if needed
If the fast speeds are still slow after cleaning, the curtain tension may need adjustment. This is done by tightening the spring that drives the first curtain. The adjustment is camera-specific -- consult a service manual.
Final verification
Test all speeds again after any adjustments. Run a test roll through the camera before trusting it with important film. Check the exposures against a known-accurate meter.
Warnings
Never touch shutter curtains with your fingers. The oils from your skin will contaminate the material and cause sticking.
Use very small amounts of lubricant. Excess lubricant is the cause of most shutter problems, not the cure.
Naphtha is flammable. Work in a ventilated area away from open flames.
Some cameras have curtains made of rubberized silk that is extremely fragile. Research your specific camera before attempting any cleaning.
Notes
I use a Calumet ShutterSpeed tester for most work. Smartphone apps like Shutter Speed Tester work reasonably well for a rough check but are not accurate enough for final calibration.
Acceptable tolerances vary by camera and by use. For a camera I'm going to use for critical work, I want the fast speeds within 10-15% and the slow speeds within 20-25%. For a camera I'm going to use casually, 30% is acceptable.
In Florida, I've found that cameras stored in humid conditions often have lubricant that has absorbed moisture and become gummy. These cameras need a more thorough cleaning than cameras stored in dry conditions.
If a camera's shutter speeds are wildly off -- 1/1000 reading as 1/250, for example -- there's usually a more serious mechanical problem than lubricant contamination. Don't keep adjusting. Find the root cause.
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