[Aavso-photometry] Differential photometry for dummies

[Tom Krajci]

>From: "R. Brian Potter" <potterrb at comcast.net>

>I have subtracted a master dark (3-5 images median combined, depending on
exposure time...

I recommend your master dark be a median combine of more images...at least
7.

If your camera is temperature regulated, and is repeatable in temperature
from night to night...you can make a library of master darks (made from
dozens of frames) on a cloudy night...and they will be usable for many
weeks.

Same for master bias frames.

That means on a given night, the only calibration frame often need to take
is the flat. (I advocate the flat box because you can do it whenever you
want.)

>3) Align individual images after dark subtraction

I don't know about CCD Soft, so I don't know if this preserves the
photometric information when you align images.  (I prefer to take measures
of individual images, then look at the scatter in the multiple
measurements.)

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Tom Krajci
Cloudcroft, New Mexico
http://overton2.tamu.edu/aset/krajci/

Center for Backyard Astrophysics (CBA)
http://cba.phys.columbia.edu CBA New Mexico

American Association of Variable Star
Observers (AAVSO): KTC http://www.aavso.org/
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