Re: [APML] Flux Calculator - with IDAS filter

["Mike Cook, AF9Y" <mwcook@concentric.net>]

>From:           	Chuck Vaughn <aa6g@aa6g.org>

> Mike,
> 
> Looks like reasonably dark skies start around 50. Central Coast, CA
> should be similar to Chews Ridge and I know how dark that is. I would
> not consider Soquel, CA to be very dark.

Well, with my 189 Flux, Soquel's 78 looks darn good.
 
Using scaling, I believe Stan's Flux measurement program can
help evaluate the impact of a light pollution filter like the IDAS
notch filter.  For my location, the light pollution filter reduced the
effective flux value from 189 to 90.  

You can't just use the background measurement with the IDAS
filter.  Here's how to calculate it:

1) Using the measurement tool in PhotoShop, caculate the area of a
    rectangle drawn on the spectrum plot from 0 to 100% and from
    410nm to 680nm.

2) Using a rectangle aproximation of each notched area, caculate
    the total area of all the notches.

3) Caculate the area of a rectangle from 100% to 95% and from
     410 to 680nm.  This is an approximation of the loss from
     transmission efficiency

4) Add the notched area and transmission loss areas to determine
    the total loss.  Divide the area from step 1 by the total loss area
    to determine the % loss.  Subtract this from 100% for the
    total light transmission.

The IDAS filter light transmisssion was caculated at 66%.

Now you can use Stan's Fux program to determine how much the
filter improves your site.  Take a measurement with the filter
in place and divide the result by the percentage (0.66 for the
IDAS filter).  Enter that for the average ADU of background.


Mike Cook, AF9Y
http://www.af9y.com
mwcook@cris.com




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