Hi TwoTone,
Thanks for the update on your build.
Putting all three sensors diagonally does allow for horizontal or vertical testing, but does make alignment a little more tricky than if they are all horizontal or vertical.
I made mine to be cheap and easy to build, thus using standard laser & receiver modules, without the need for 3d printed parts or bespoke pcbs. I'm more than happy for people to make these or add pretty boxes, adapt or change to their taste. I'm also more than happy for feedback, ideas & suggestions for improvements & additions.
There is no reason why a large light source could not be used, in place of the lasers, with the rx sensors positioned in the film gate.
I can trigger mine with white card reflecting from the computer monitor. Actually, that gives me an idea
)
Mine will work with either the lasers or sensors in the film gate, although most people did not like the idea of lasers pointing into their camera.
The other reason not to use a large light source, other than adding complexity is that I did not want people electrocuting themselves.
Adding a light-meter to the shutter tester is very easy. I already have all the code from my exposure meter project. A reading in lux & EV can be displayed. The light meter sensor has a rated un-calibrated accuracy of 20%. Calibration is easy, the sensor allows for this within firmware, but one would need a calibrated light source to compare.
Control of the light could simply be a dimmer switch, available in any hardware store (of the correct type for the light, tungsten, LED etc) or adding pwm control from the shutter tester, but this again adds complexity & the risk of electric shock.
The Reveni tester looks interesting, but I cannot see it being any more accurate than mine. It is doing the same thing, measuring how long the light is seen for. The trick is to have very tight code to capture the timings with minimal latency.
I'm not an expert on leaf shutters, so cannot see how a computed shutter speed can be achieved with just one sensor (or else we could use just one sensor for focal plane shutters?) Mine will measure the raw speed of a leaf shutter, but then there will be some error due to the much discussed width of the sensor. If anybody has any ideas, please let me know & I can change the leaf shutter/single laser code.
As Chuckroast says, one should not be troubled by absolute accuracy. Old spring driven cameras will vary shot to shot, be affected by temperature etc. Consistency is more important. Film has a wide exposure latitude (not so much reversal, but who uses that?) and compensating developers & auto printing labs also play their part.