[Aavso-photometry] Linearity test puzzle

[Wolfgang Renz]

FYI


----- Original Message ----- 
From: "Chris Peterson" <cpeterson at earthl...>
To: <SBIG at yahoogroups.com>
Sent: Saturday, February 05, 2005 7:20 PM
Subject: Re: [SBIG] ST-10 Image Ghost in Darks

John-

When you are exposing the CCD, it is just sitting there with no electronic 
activity going on. In other words, there is no difference between a 
10-minute flush and reading a bias frame. The actual flush occurs with the 
readout of the data. So for time-decaying residuals, you can just wait (or 
speed things up by allowing the sensor to warm up). For residuals that can 
be removed by flushing, just download a bunch of bias frames. It is 
important to note that both types of charge retention mechanisms can exist, 
and it seems to vary from camera to camera. Most ghosting with my ST8i is 
effectively removed by flushing, other people using the same camera have 
found that flushing doesn't work for them.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com



----- Original Message ----- 
From: "Chris Peterson" <cpeterson at earthl...>
To: <SBIG at yahoogroups.com>
Sent: Saturday, February 05, 2005 7:14 PM
Subject: Re: [SBIG] ST-10 Image Ghost in Darks

Definitely try to take your darks when the camera has first cooled down, or 
during another session altogether. If you have to do them after imaging a 
bright target (like M42) you can effectively clear the residual charge by 
allowing the chip to heat up and then cooling it down again. That only takes 
about five minutes, so is pretty practical. Download a few bias frames while 
the sensor is warm to help flush the charge.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com



----- Original Message ----- 
From: "John Smith" <johnzonie at comcas...>
To: <SBIG at yahoogroups.com>
Sent: Saturday, February 05, 2005 11:13 AM
Subject: RE: [SBIG] ST-10 Image Ghost in Darks

Howard,

It is mostly a time-related decay.  What I do before taking darks is to
take a 10 minute flush frame or two, which are discarded, and then
take my real darks after that.

John



----- Original Message ----- 
From: "howardmaron" <hmaron at attglo...>
To: <SBIG at yahoogroups.com>
Sent: Saturday, February 05, 2005 10:59 AM
Subject: [SBIG] ST-10 Image Ghost in Darks

Last night for the first time I experienced very severe ghosting of
the images of M42 in my darks. I have seen discussions regarding this
phenom. but have not experienced it. It is so dramatic that I am
surprised the discussions have been so limited regarding this matter.
The ghosting persisted throughout sequential darks so I saw no
evidence of decay with "flushing". Curiously these occured after very
short m42 light sequences (8 sec.) The darks contained linear full
frame streaks as well. CCD Temp was -20 C (which I gather can
contribute to residua)

Any practical suggestions?

Obvious conclusion is darks before light BUT certainly the gurus have
integrated a fool proof method I need to learn to avoid this
annoyance.

Thanks for any suggestions

Howard