Issue:

old camera's shutters aren't accurate and photographers need to know exactly what the shutter speed is to have proper exposure.

proper solution:

find somebody to do a CLA to your camera. Would be nice if it was possible as this knowledge is almost gone and remaining service people are too busy anyway

my solution:

just get the actual shutter speeds and expose accordingly

Requirements:

* measure a pulse of light with period of 1s to 1ms;

* minimal effort;

* accurate enough and repeatable enough;

* made with parts I have at hand;

Hardware:

Given the requirements I came up with device - I picked up esp32 board with oled display built in (because I am lazy) and connected photo transistor to one of gpios. I also added 5V external pullup as I expected it to produce sharper wave fronts. It seems to work ok, but I haven't tested with internal pullups and 3v3.

For light source I used a phone's flashlight: even though glass does not allow IR to pass through and photo transistors are most sensitive to IR, the source seems to be strong enough for device to trigger. 

Software:

I written some code with arduino to measure pulse length and display the results on the screen. To get photographer friendly representation of data you need to convert time to frequency and display it as fraction of seconds, so 1 kHz would be 1/1000s. 

I attached all code in files for anybody who wants to take a look

How it works: 

1. open the back of the camera to expose the curtains:

2. point the camera to light source (could be flashlight or bright window)

3. Wind the shutter

4. Power on or reset the shutter meter and point it at the curtain in the spot of your interest 

5. release the shutter and check out the results on the screen

6. if device shows timeout, then it means you did not release the shutter in 10s after starting shutter meter, Just repeat all the steps.

Not sure how helpful this device is, but is way more user-friendly than doing same thing with oscilloscope