You dont need any of this since light meters (used or new) already exist on the market, and film has anyway a lot more range to work with than digital exposure. You can over expose film many times and the picture would still look fine. It's not linear at all.
You really don’t need this when you have a phone in your pocket. When I’m shooting film I just use a light meter app, and it’s more than accurate enough because of the dynamic range you described.
Obviously this is more for your hobbyist. There are likely limitations, but I’ve not hit them myself.
> You really don’t need this when you have a phone in your pocket.
Light meter apps give quite different results from the usual light meters used for analog cameras. Probably good enough for the intended use, but it's not exactly the same thing.
Film is nowhere near the dynamic range if digital cameras nowadays. You can over or under a digital image by a factor of 32 and still get a useable image though the highlights might clip or you might have noise inherent to the exposure.
In fact, many modern cameras are ISO invariant, meaning that as long as you have enough light hitting the sensor, your ISO basically doesn't matter at all.
And that's only for black and white film. Color film has much worse dynamic range.
To put number on it, the ratio between the dimmest and brightest spot you can record is around 2^15 for a modern full frame camera. The best films will give you 2^13 from no noticeable exposure to depletion of the halides, and the worst around 2^4.
All that said, it's not clear that this raspberry pi unit has any kind of flash mode, so the price difference vs. the industry-standard Sekonic 308 ($200) becomes less favorable.
