Flats & ADU madness with the red filter

[IanL]

It has never occurred to me to make my flats at exactly the same exposure value as each other and I've never ever done so, so all the pictures I've ever posted have been calibated by flats varying over a range of two or three thousand ADU. Next time I take flats I'll take two different values for one channel and compare their effect on the image. Given that the flats application is by division I'm near certain that it will have no effect whatever. Clearly this is not comparable with darks which are very sensitive to temperature and work by subtraction. Even a slight mismatch in ADU values due to temperature (or anything else) is a disaster. But flats? I'm betting it is totally unimportant.

Practical example here:

http://darkhorseobservatory.org/index.php?CategoryID=62

The upshot for a mono camera with filters it isn't a big deal provided you aren't drastically underexposing your flat or saturating it. I guess the advice to shoot for an average that is about a third of the maximum ADU value is simply to avoid the possibility of saturation. There is no real need to match exposures across the flats, so using a 21.5K R, a 23K G and a 34K B should work fine.

The situation is a bit more tricky for a OSC/DSLR camera since you have to get a reasonable ADU count in all three channels from a single exposure duration, but it proves the point since it would be very difficult to achieve the same average ADU count across all three. (Maybe using a light source where you could tune the brightness of the R, G, and B components separately, can't think how else you would do it?)

It does seem odd that your ADU is changing so much for a fraction of a second of exposure (and worth investigating in case it is having a similar effect on the light frames).

[Tim]

I'm not sure it's worth even figuring out, if indeed anything needs figuring out, because overall performance isn't affected, compromised or altered.

Maybe Steve and Co will email back out of courtesy, but If I was busily preparing for astrofest, then hypothesising about something that doesn't matter much wouldn't be high on my list either.... :s

[ollypenrice]

I'm not sure it's worth even figuring out, if indeed anything needs figuring out, because overall performance isn't affected, compromised or altered.

Maybe Steve and Co will email back out of courtesy, but If I was busily preparing for astrofest, then hypothesising about something that doesn't matter much wouldn't be high on my list either.... :s

Blow Astrofest, he has to fix my 11 Meg first!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Olly

[opticalpath]

Blow Astrofest, he has to fix my 11 Meg first!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Olly

If I see him on Saturday I'll tell him you were asking after him, Olly

Adrian

[Tim]

When I next do my flats i'll do the same test if it is of interest to you Sara? I have a 460 and Baader filters too.

[swag72]

Cheers Tim - I would find that interesting if you have the time. Meanwhile I'll lower the light intensity and see how that goes!

[swag72]

Just had an email from Vince at Atik - I am very appreciative that they got back to me at this busy time for them - Saying that Steve was aware that this was a problem and they are planning on a firmware fix soon.

[Mike_F]

Just had an email from Vince at Atik - I am very appreciative that they got back to me at this busy time for them - Saying that Steve was aware that this was a problem and they are planning on a firmware fix soon.

Superb! Might just have to thank them in person for that news at AstroFest tomorrow..

Thanks for letting us know Sara.

[Mike_F]

Just spoke to Steve, the new firmware is ready and should be up on the web site next week.

[swag72]

Brilliant Mike, thanks for letting me know - I'll keep an eye out !!!