From: "cwskas" <cwskas@earthlink.net>

Date: November 22, 2009 1:43:09 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: measuring brightness

I am reviewing various parts of the AstroIIDC manual and trying out some things I havent used yet.  For the last couple of hours I have been using the Measure Brightness option.

I first put the cap (which I use to capture darks) on my camera and ran 60 secs, using 33ms exposures and 399 brightness with a measure brightness area of 640x480.  I opened the file, selected all and copied the data.  Then I pasted into a Numbers spreadsheet which calculates the average and the median values.

Pretty impressive.  I calculated a median of 1595 and average of 1597 for my DMK21AF04, 640x480, 8 bit camera.  If I have this straight (640x480x255=78336000) that looks like only .002% of the maximum.  Seems like a pretty good dark to me.

Just out of curiousity, I removed the cap and measured 60 secs of light frames in my living room with the security lens (it was on there for the darks also) using the same settings.  The average/median for the same number of frames turned out 4566613 & 4390629.

That was a lot lower than I expected, 5.830% average.  The image in the house is fairly dark.  I didnt try to set the iris or anything like that.  But my TV is on, in the frame and pretty much in focus.  There are areas of saturation in various parts of the frame.

Now, if there are any Numbers gurus out there, please contact me via the email below.  I want to improve the spreadsheet and cant figure out how to do what I want.

Willie

willie@igc.org