Since I started the hobby of repairing cameras, I built a couple of shutter testers. The first was based on the classical approach of a light source (a laser diode) and a photodiode, with a microcontroller measuring the exposure time. Very accurate.
Another was based on a cathode ray tube (CRT) display. (https://www.dpreview.com/forums/post/67651256 ). In conjunction with a digital camera it also allowed to visualise the speed of the curtains along the frame; useful, but a bit clumsy.
What I really wanted was something more visual, like the old Leica ones that were based on a rotating drum and enabled the technician to assess the exposure by eye, as in the picture below.
A snapshot from the service manual of the Leica IIIf
I also didn't want moving parts, so rotating drums were out of question.
The solution was simpler than I expected. Strobing a LED panel was all I needed! The strobing pattern consists in a very short flash of light (e.g. 40 us) repeating at a rate similar to the exposure time to be tested, e.g. 1/1000s. Interestingly, it also works with digital cameras! The idea is that if the strobe flashes at 1/1000s and you look at it through a shutter firing at 1/2000s, you see alternating light/dark stripes with approx having the same width.
The eye-based shutter tester
Same, with a camera ready to be tested
The strobe speed can be changed. If set at 1/000 s, a shutter at 1/2000s will show alternated bright/dark stripes with approx the same height:
1/2000s
As the shutter under test gets closer to the nominal 1/1000s speed, the light stripes get wider and the black ones get narrower.
1/1300s
Ideally, at exactly 1/1000s the image should appear illuminated uniformly
Nominally 1/1000s. There is a hint of a dark like at the bottom, meaning that the shutter speed there was faster than 1/1000s. Moving upwards, lighter bands appear, indicating an exposure very slightly longer than 1/1000s. The exposure is not perfectly uniform along the frame, but less than 1/3 stop.
1/500s. The light stripes overlap giving brighter stripes. Approx 50%/50% height means 1/500s.
These pictures is what an eye would see when testing a film camera, but in reality were taken with a Lumix S5 with a macro lens pointing at the strobing light, so they are representative of the performances of my S5's shutter.
In a dark environment and squinting a little, it also work with bottom-loading cameras if one inserts a white piece of paper instead of the film and uses the strobe LED to illuminate the shutter curtains from the lens mount.
The tester is really easy to build and very intuitive and quick to use. It has rapidly become my favorite option when adjusting a shutter. I go back to the laser-based one only when I want a final, numeric test report!
Another was based on a cathode ray tube (CRT) display. (https://www.dpreview.com/forums/post/67651256 ). In conjunction with a digital camera it also allowed to visualise the speed of the curtains along the frame; useful, but a bit clumsy.
What I really wanted was something more visual, like the old Leica ones that were based on a rotating drum and enabled the technician to assess the exposure by eye, as in the picture below.
A snapshot from the service manual of the Leica IIIf
I also didn't want moving parts, so rotating drums were out of question.
The solution was simpler than I expected. Strobing a LED panel was all I needed! The strobing pattern consists in a very short flash of light (e.g. 40 us) repeating at a rate similar to the exposure time to be tested, e.g. 1/1000s. Interestingly, it also works with digital cameras! The idea is that if the strobe flashes at 1/1000s and you look at it through a shutter firing at 1/2000s, you see alternating light/dark stripes with approx having the same width.
The eye-based shutter tester
Same, with a camera ready to be tested
The strobe speed can be changed. If set at 1/000 s, a shutter at 1/2000s will show alternated bright/dark stripes with approx the same height:
1/2000s
As the shutter under test gets closer to the nominal 1/1000s speed, the light stripes get wider and the black ones get narrower.
1/1300s
Ideally, at exactly 1/1000s the image should appear illuminated uniformly
Nominally 1/1000s. There is a hint of a dark like at the bottom, meaning that the shutter speed there was faster than 1/1000s. Moving upwards, lighter bands appear, indicating an exposure very slightly longer than 1/1000s. The exposure is not perfectly uniform along the frame, but less than 1/3 stop.
1/500s. The light stripes overlap giving brighter stripes. Approx 50%/50% height means 1/500s.
These pictures is what an eye would see when testing a film camera, but in reality were taken with a Lumix S5 with a macro lens pointing at the strobing light, so they are representative of the performances of my S5's shutter.
In a dark environment and squinting a little, it also work with bottom-loading cameras if one inserts a white piece of paper instead of the film and uses the strobe LED to illuminate the shutter curtains from the lens mount.
The tester is really easy to build and very intuitive and quick to use. It has rapidly become my favorite option when adjusting a shutter. I go back to the laser-based one only when I want a final, numeric test report!
