I post things here.

I got myself an old rangefinder film camera. I did some quick verifications, and although everything seems to be working well, I'd like to test the shutter speeds as cameras tend to get sluggish after decades. This camera is 55 years old so that's to be expected, but I want to know by how much.

So there's an opportunity for a cool little project here.

So how to test the camera's shutter? There are a few Arduino projects for that purpose, but my only Arduino board is in use. I do have a shiny RP2040 board lying around unused that was only used for some quick experiments, so I thought I'd try and make my own version of a shutter tester with parts I already have.

Behold the shutter speed tester in all its glory and ignore the mess of wires...

Ingredients: RP2040 board (Raspberry Pi Pico W), an OLED display (SSD1306, 128x64), a KY-008 laser module (5 mW), a photo-resistor (salvaged from a dead KY-018 module, specs unknown), two push buttons, a DIP switch, a resistor (1 kΩ), a breadboard, a bunch of dupont wires and of course Lego blocks.

The first non-working prototype used a infrared led/sensor, but I inadvertently burned it and it was the only one I had, so I had to change plans and used a laser, and this brings me to a disclaimer: a 5 mW laser is quite low-powered, and while it's unlikely that it could cause severe damage to your eyes, always assume it will. Do not look at the beam. I'm not responsible for your loss of eyesight. On that topic, the DIP switch is there so the laser is only powered when needed.

In a nutshell the camera sits between the laser and the sensor, and the RP2040 measures the time the laser hits the sensor while the shutter is open.

The laser should be aimed at the sensor, and for consistent readings, the laser, the sensor and the camera must not move, and this is when Lego bricks come handy to bracket the camera, sensor and laser emitter.

Ideally, the laser should be aimed closest to the center of the lens.

This camera has a fixed lens, so the beam must be aimed through the lens to factor to correct the refraction caused by the lens, changing the direction of the beam.

Using the bulb shutter setting (or the lowest speed available) is a big help to fine tune the sensor/emitter placement.

The Lego brackets worked perfectly, the camera didn't move.

There are two buttons, the "select" and the "reset" buttons. The "select" button cycles through the different shutter speeds defined in the code and the "reset" button resets the different readings for the current shutter speed.

Select the desired speed in both the camera and tester, wind the shutter and press the shutter button. The reading will be shown in display, and can be repeated multiple times. The first line shows the selected shutter speed, the second show the measurement in microseconds and the discrepancy in percentage, and the third shows the real shutter speed in the 1/x seconds notation.

The refresh speed of the display wasn't in sync with the camera's shutter speed, so the last line appears partially erased.

Of course, I haven't calibrated this thing, nor compared the results to a real shutter tester machine. So as usual, no guarantees here.

You can download the diagram ^(PDF) and the MicroPyhton code ^(ZIP) that also includes the SSD1306 library for the display.

And because I don't know the exact specs of the photo-resistor (multimeter shows an inconsistent 100 Ω to 2 MΩ range), I had to guess an appropriate threshold for the light detection with a few tests in order to avoid false positives with ambient light. You might need to adjust the threshold_volts variable in the code for your particular photo-resistor.

As always, if this project burns down your house, it's not my fault!

My Olympus

Results: 1/500 (-75%), 1/250 (-3%), 1/125 (-15%), 1/60 (-14%), 1/30 (-14%), 1/15 (-13%), 1/8 (-9%), 1/4 (-24%), 1/2 (-20%), 1s (-11%).

For the Olympus, almost all speeds are good and within the acceptable 30% threshold that is equivalent to 1/3 stop, the exception is the faster shutter speed (1/500) that is off the mark by 75%. It looks like this is pretty common for the faster speed in old cameras. I have to keep this in mind while shooting.