Re: [ATM] Dark Sky Meter

["Jim Miller" <jim@jtmiller.com>]

Hi Dom

My reason for a PIN was simplicity. I've built production photon counting 
systems with PMTs in the past as well as APDs and found them too fussy and 
expensive. I'm sure I could build a system for myself with either but I 
wouldn't meet my goal of having the system widely reproducible for parts 
cost under $100.

With a 75mm diameter f/1 lens (numbers taken for simplicity not 
availability) the signal from Vega only generates about 4 picoamps in a 
PerkinElmer VTB1013B (chosen for match to visible.) This is comparable to a 
mag19+ sky. So measuring down to mag21+ would mean another 6X reduction in 
signal.

I'm pretty sure I could build a preamp based on an LMC6061 and associated 
circuitry but I'm not sure that femptoamp current measurement capability 
could be maintained "in the wild" and even less sure that the Average Joe 
could build one.

Hence I labeled my effort impractical rather than impossible.

Not trying to deter others from creating their own design but just stating 
my own goals and lack of progress.

dark skies!
jtm 

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