Atik 460ex - what ADU level for Flats ?

[pilkinn]

I'm taking flats with a EL panel for my Atik 460ex. What average adu value should I be aiming for?

Thanks.

Neil.

[ollypenrice]

Try about a third of the way up. The general rule is a third to two thirds with recent thinking being high. I'm old school and go for a third. I doubt it will matter. In Artemis Capture (lovely software) you just look at the white point on the display. In case you haven't come across this bit of info, though you probably have, a master bias will do fine as a dark for flats - ie any and all of your flats. No need to do dedicated ones for each flat.

I'll be trying one of these cameras myself soon and am really looking forward to it. What a chip it seems to be!

Olly

[pilkinn]

Hi Olly. I'm using MaxIm. I've read that it should be 1/3 to 1/2 of the full well capacity of the pixels on the chip. For the Sony chip this is 20,000. Does that mean I should be aiming for the flats peaking at between 7000 to 10,000 ? Or is the 20,000 some other value?

[ollypenrice]

It's confusing. Most people, myself included, thought in terms of the 65000 counts. Recent discussion, and research by RobH posted on here, reveals that this is not the real well depth. So, yes, try 8 to 10,000 and go higher if you need to. By going higher it can be argued that you need fewer subs to elilminate noise but in your case the noise will be slight. Besides, if you knock out thirty or forty of each, which is easy, it takes little longer than taking fifteen. The thing about flats is that you know when they are working or not working. It is pretty obvious in the image. Clearly in exposing to a half to two thirds of 65000 I was exposing to far more of the real well depth than I thought but the result strikes me as perfect all the same.

I use a Neumann panel and take them only in the dark. They never work if I take them in the light because I always get a gradient. It's capturing good ones that is harder than applying them! The application part seems quite tolerant.

Olly

[pilkinn]

I also use a Neumann in the dark after the imaging run, I just move the telescope so that it's vertical and just place it on the end of the dew shield. Works fine, although I was surprised at just how much exposure I have to give it when using the Ha and SII filters.

I've done a bit more reading about saturation levels, ADU counts etc. The 460ex's Sony chip is quoted with having a 20,000 e- full well capacity. However the system gain on the camera is set to 0.3 electrons per ADU. So ..... 20,000 dived by 0.3 = 66,666 which is not far off the max ADU count with 16 bit cameras (65,536). I'm guessing it isn't by accident that the gain has been set to 0.3. So, to get a third of the saturation point for the 460ex an ADU count of 20,000 would be about right. I suppose other cameras with a different full well capacities and gains would have different requirements for taking flats.

[ollypenrice]

Thanks for the post. It's a good one!

Olly