Kurt: Not to be picky about your math, Kurt, (OK maybe I am being picky but it's one of my favorite math/astronomy puzzles) but the size of a 90 circle of sky is 1.84 steradians. The fomula for an XL spreadsheet is =2*PI()*(1-COS(RADIANS(DIAMETER/2))) and the numbers this gives are 360 = 12.57 180 = 6.28 90 = 1.84 45 = .48 The smaller the field of view the closer the diameter to area approaches a power of two. Very small angles are essentially on a nearly flat surface but the difference starts to be measurable even at 90 degrees. DT --- On Tue, 12/15/09, Canopus56 <canopus56@yahoo.com> wrote:
From: Canopus56 <canopus56@yahoo.com> Subject: Re: [Utah-astronomy] Cheap meteor camera? To: "Utah Astronomy List Serv" <utah-astronomy@mailman.xmission.com> Date: Tuesday, December 15, 2009, 10:57 PM Patrick,
The magnitude reach of any sensor is also limited by the signal strength in terms of light gathering as measured in radiance (Watts per sq meter per steradian). There are 12.57 steradians in a sphere, 6.27 steradians in half sphere dome and 3.18 steradians in a 90 deg TFOV.
As you increase the TFOV from 90 to 180 degrees, the signal per square meter of your camera chip is halved. This may inherently cap the telescopic limiting magnitude of any all-sky camera to very bright objects regardless of the state-of-art of CCD chips.
The expensive discontinued SBIG All Sky Meteor cam quoted a TLM of mag 4. http://www.sbig.com/products/allsky.htm (with sample output images)
It used an "ST-402ME mated to a 2.6 mm focal length F/1.6 CS- mount lens" yielding a TFOV of 90 x 140 degrees. http://www.sbig.com/products/402_new.htm
- Kurt
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