Welcome aboard @bjpirt and congratulations on this very interesting project! I like the elegance of the mechanical-electrical solution, requiring no additional housing etc. I hope you'll stick around on the forum to answer any questions that members will undoubtedly have.
I actually just use a couple of small pieces of Blu-Tak - it sticks well and isn't too close to the shutter. However if that makes you nervous you could use an elastic band or some masking tape.How do you attach the sensor to the film window?
Not at the moment, but if there's enough interest I might make a small batchIs it possible to buy a finished device or have it assembled?
What's it's accuracy and how have you verified it?
can this be used as a stand alone tester hooked directly to an off line computer using a program via usb?
Open a serial terminal to the ESP32 (this is built in to the Arduino IDE). You'll need to connect at 921600 baud.
Fire the shutter and it will print out the timings to the serial console. There are two sets of timings:
- The time taken for each shutter to travel across the frame - it's important to try and get both shutters moving at around the same speed
- The time each sensor was exposed for in microseconds, milliseconds and fractions of a second
What's it's accuracy and how have you verified it?
It doesn't, but that's the beauty of open source. I made this to scratch my itch and you're free to modify it as you see fit. For me, the web interface adds a lot of utility like being able to easily average up multiple readings and perform deeper analysis than you would be able to do with just a serial or screen output. Basically, I got sick of entering readings manually into a spreadsheet when calibrating a camerawhy does a shutter tester have to be bluetooth and involve web sites?
"uses Bluetooth to communicate the measurements to a web page that ...."
so what does this mean in the op post?
The sensors itself have a delay of 0.1-5us or so, depending on how they're implemented. Let's say single-digit delays.
The sensor readouts are interrupt-driven; typical inaccuracies in those ISRs (interrupt service routines) is in the order of the low-single microseconds.
Add to this the inaccuracy of a typical crystal that's used to time the ESP32 - this will be 40ppm or so, worst case.
So let's say this adds up to 10us, which is a particularly dark scenario. A 1/8000s shutter speed = 125us, so the timing on that one might be off by 8%, which is less than 1/3 of a stop. Again, that's very much a worst-case scenario.
So you don't know how accurate (or inaccurate) it is when measuring real shutters then.I've compared the timing against a Salae logic analyser and the Arduino was within a microsecond or so of that timing which I was pretty happy with. I haven't yet added compensation for the sensor width which will have more of an impact when measuring faster shutter speeds but I will be adding this shortly.
So you don't know how accurate (or inaccurate) it is when measuring real shutters then.
All of little relevance.
The accuracy will depend much more on how it detects the curtains, width of sensors, angle of light source etc. etc. and not on the component tolerances.
I want to compare it against a known good tester - if anyone is able to help out with this I can send them one to play around with. If you have any suggestions on good ways of checking accuracy I'd be keen to hear them
All of little relevance.
The accuracy will depend much more on how it detects the curtains, width of sensors, angle of light source etc. etc. and not on the component tolerances.
So do the same analysis for those factors for a realistically pessimistic scenario and tell us the outcome.
It's easy to be critical of someone's work; contributing constructively is more challenging, but a lot more interesting.
I want to compare it against a known good tester - if anyone is able to help out with this I can send them one to play around with. If you have any suggestions on good ways of checking accuracy I'd be keen to hear them
It's the guy who designed it and is trying to sell it to prove it works
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