Re: [ATM] Calibration Ideas for Dark Sky Meter (aDSM)

[Nicholas Peshman <joviansoftware@comcast.net>]

As For the artificial source why not have a couple of polarization
filters in front set to some designated angle. this way you could easily
get anywhere from 0% transmission to 50% of the original brightness. And
I don't think it would be terribly difficult to set up properly.

Nic

On Sun, 2004-10-03 at 10:24 -0400, Jim Miller wrote:
> Hi All
> 
> I'm looking for "absolute" calibration ideas for my absolute Dark Sky Meter
> (aDSM). My current idea is to use Vega at zenith on a "clear" night to give
> me a mag0 reading. Looking at Cart du Ceil at the area around Vega with a 1°
> FOV shows only a few relatively dim stars which should contribute to a
> calibration inaccuracy well below the measurement precision of this
> instrument. In operation one would point to Vega on a suitable occasion,
> press the calibration button and the unit would establish that as Magnitude
> 0. All other measurements would ratiometrically derive from that stored
> value.
> 
> Others have suggested several potential problems with this approach
> including clouds, haze, unsuitability of Vega at other lattitudes and times
> of year.
> 
> The problem with artificial sources that I can see so far is that it is
> difficult to get their magnitude and color temp down to starlike levels so
> as to remain within the dynamic range of this device. If anyone has some
> ideas for obtaining a suitable artificial source I'd be grateful.
> 
> As far as the electonic part of the design that's coming along pretty good.
> I'll post a schematic and parts list on my website (www.jtmiller.com) in the
> next week for anyone who's interested. I'm planning to build three units
> initially to compare the results among them. Then I'd like to send two of
> the units to interested parties who could try them out.
> 
> The goal is to have anyone with the requisite technical skills to be able to
> buy the parts and build one.
> 
> jtm
> 
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