CCD temperature for flats - Forums

Flats continue to plague my efforts. Question of the day is, "Do flats need to be taken at the cooled temperature equal to the bias frames, or not"?
thx
Charles

I take flats at the cooled temperature to eliminate as much noise as possible. I also use the same temp as the bias. But the dark noise from the bias should be minimal so the temp difference shouldn’t be important.

Maybe someone has the math on this though?

As far as I'm aware flats do not require that you have the same temperature as your darks or lights. Your focus, position of your CCD camera and any filters, reducers, flatteners, in your optical train must remain untouched or unchanged. Also your flats should be the same ISO or gain setting as your lights, I also would keep the same black focus too. Hope this helps.

Jirair

Thank you gentlemen..Gain setting on my CCD is a new piece of information I will research…This was the first time I had different temps (cooled bias and summer hot flats). I can't get Pixinsight to remove the bias streaks from the flats and I guess maybe the temperature difference was too much; 3C for biases and 34C for flats. Maybe I will just have to take the extra step each time like Kevin mentioned.

Happy star hunting,

Charles

Charles,

It should not require a lot of extra work - just shoot the bias one time a the temperature you normally shoot your lights a flats at. It only takes a few minutes to shoot bias so should be no biggie. But the problem may not be the temperature.

In in any case, I would expect you to be shooting at temps below zero. Is your CCD not cooling to below zero temps at night?

kevin

Yes it cools very well (Atik One). But I have been shooting flats in the heat of the afternoon, over 90 degrees outside, and didn't want to push my luck achieving cooling. So I shot 3C temps for LRGB since I was just doing a globular cluster this time…and incidentally, the only frames I chose to shoot at a different temp this time were the flats..Already did all LRGB flats. Working on it one more time tonight to see if I can process around that, but don't see much hope.

I have always been told flats are not temperature dependent, but I know that Sara Wager always cools her flats. So I tried it, and I can't say I noticed any difference.

So basically its not essential, but do them with or without as you feel best.

Carole

Thanks so much Carole..

i do cool down my camera when shooting flats….

Thx Diego..I'm leaning toward doing the same from now on..

Heat adds to the noise in your detector. Cool the camera, let it stabilise for 30 min. Then do your calibration runs. Depending on the software used, you can script your calibration runs, say, DARK, BIAS, DARK BIAS. etc. Same for you Flats, cool the camera, stabilise, and do your runs.

On my system, small changes in temperature effects the BIAS frames and I can see this when I calibrate the subs.

Thx Terry. I will do just that..

When I used to use an Atik camera I had major issues until I started to cool the flats down… in fact I ended up cooling all frames down to the same temperature as the lights and I never had any issues after that. In fact this was the recommendation by Atik to someone I know as well, who had a similar problem. Hope this helps. Simon

Thanks Simon. I noticed the same at this point..cooling it shall be..