[Aavso-photometry] Linearity test puzzle

[Ben Davies]

Hi Vello,

I saw a similar response when testing my ST-10.  It wasn't as consistent 
and repeatable as your results seem, but I saw the anomaly  frequently 
enough that I came to be very suspicious of the first image in a series.

http://ben.davies.net/st-10a.htm

There are 5 minutes between images in the series sets I was making.  My 
first guess (and that is all it is) is that the the acquisition software 
is somehow doing this.  I have been using SBIG's CCDOps, but also have 
CCDSoft and AstroArt.  Sometime this week I will give them a try and see 
if I can make any  improvement.

By the way, It takes 24-36 hours for my led source to settle down to a 
reasonably stable state.  There is a thread on the AIP site "constant 
light source" from a few weeks ago where this was discussed.  Bruce 
Anderson found an interesting feedback circuit which purports to produce 
a stable led output.  
http://groups.yahoo.com/group/AIP4WIN/message/6537  I may give this a 
try soon.

Ben Davies