More FLATS !

[pscammp]

Hello again,

More FLATS !

Ok, take a look at the attached image of a single Flat which has not been De-Bayered

This is a sub 1 second Flat exposure using a QHY8L at around 0.3 sec's

[pscammp]

Now take a look at the same Flat which HAS been De-Bayered just to show what's where in this surprise wave form:

[pscammp]

This is what a 30,000 ADU Flat looks like exposed above 4 Sec's, was around 18 sec's to get the 30,000 ADU's as
it had lots of sheets of paper over the EL panel to get exposures above 4 sec's for ADU options from 12,000 ADU's
to about 30,000 ADU's to get the camera out of the dual readout mode.

Just in case it matters the 8L's Gain is set as 10 and Offset set at 117, it has a clear glass front instead of the
standard IR blocking one and there is a IDAS P2 filter on the front which deals with LP and IR at the same time.

Have I got a serious problem with my CCD

? ? ?

Many Regards
Paul

[jkmorse]

The quick answer is I don't think you have a problem CCD.  What you are seeing is the sensitivity of the CCD to a blue sky in the different channels.  As an example, for my monochrome CCD, when shooting dusk sky flats, I have to stack my series so that I shoot with my red filter first, then green, then blue because red is the least sensitive, then green and blue is the most sensitive.  I need that to get comparable ADU counts with comparable iteration times.  That is exactly what you are seeing in your color flat but compressed because all the channels are being shot at one time.

Sadly, since I have never worked with flats using a color CCD, I can't tell you how to deal with that issue.

Hope that helps,

Jim 

[chris.bailey]

EL panels light emission is not white and your CCD sensitivity is not the same in R G and B PLUS you have the LP filter which skews things so this is all totally expected.

OSC CCD's are a bit of a pain to get exposure right so that all three colour channels have a decent ADU level so it ends up a bit of a compromise. Your 30,000 ADU flats should work fine but the bottom line it to try them and see. For my OSC colour camera I aim for about 25,000 peak accepting this will be nearer 15,000 at worst, the LP filter on your may well skew things more.

Chris

ps you might want to remove a few sheets of paper to get those exposure times down to avoid having to calibrate the flats with flat darks.