[sac-forum] Étendues Big and Small

At last night's meeting, we learned that Large Scale Synoptic Survey has a 
large Étendue, which is defined as the telescope's light gathering area 
multiplied by the field of view.  The Étendue for the LSST is 319 m^2 deg^2. 
 
I became curious what the Étendue is for my 10" and Philips ToUCam when it's at 
the same image scale of 0.2" per pixel.  I calculate 0.0000480 m^2 deg^2. 
 
The Étendue of the LSST will be 6.6 million times larger than my backyard 
setup. 
 
Tom

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