Comments on Why do these photometric observations of Betelgeuse look “quantized” in 0.1 magnitude steps? suggest that these are visual estimates, mostly (but not all) to 0.1 magnitude resolution.

Are there any designs for simple photodiode-based amateur photometers for stellar brightness measurements?

Just as an illustration of the kind of thing I'm asking about, I'm imagining a pair of binoculars with a 1 mm photodiode suspended by its wires the focal plane of one eyepiece, and a Raspberry Pi recording the photocurrent (with a small amplifier) and audio simultaneously ("I'm now measuring xxx... mark!") The data would be jumpy but presumably would reach a plateau whenever the star fell on the active area of the diode.

Or is this too impractical and not backwards-compatible with existing data?

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    $\begingroup$ It might be easier and more accurate to take photos of the variable star and its surroundings. Then, you could also compare the brightness of non-varying stars to calibrate your reading, so that a night of poor visibility doesn't skew your results. $\endgroup$ – Ghedipunk Dec 26 '19 at 23:38
  • $\begingroup$ @Ghedipunk sure, if it works well that would be a great example and answer. I guess you have to spread the light out over enough pixels so that the missing light in the gaps between them averages out, perhaps a small defocus... The pinhole + photodiode (or just pinhole-sized photodiode) wouldn't suffer that particular problem, but then there's the problem of nearby objects that imaging might handle better. $\endgroup$ – uhoh Dec 26 '19 at 23:42
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    $\begingroup$ Or, (assuming you're not observing Polaris) use a non-tracking tripod and a long exposure. The Earth will take care of spreading the light out across a few pixels. $\endgroup$ – Ghedipunk Dec 26 '19 at 23:43
  • $\begingroup$ @Ghedipunk bingo, that works! slightly related $\endgroup$ – uhoh Dec 26 '19 at 23:47

It should be doable with a standard photographic setup, a star catalog with distances and measurements for a some standard stars and a bit of software.

With the usual "ritual" for obtaining images from the sky with a given setup, chip and temperature (obtain dark frames, flat field frames and ground noise frames for division and subtraction) one can calibrate the brightness of an area (subframe around a star) in a photography by comparing it to known stars. The capture software or one of the many post processing packages for amateur astronomy can calculate the brightness of a region, if it is not totally saturated, i would guess if it is well away from any saturation.

A more detailed description: http://www.bellatrixobservatory.org/cvaaI/17/

Edit: An add-on script for one of the amateur software packages for doing photometry: https://pixinsight.com/doc/scripts/AperturePhotometry/AperturePhotometry.html.

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    $\begingroup$ Oh, that's quite an interesting link! $\endgroup$ – uhoh Dec 28 '19 at 14:07

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