Taking darks with a 400D

[John K]

This is one for the deep sky guys, and shows the low level of understanding I have at the moment.

I am planning a dark sky astro trip this weekend and I am hoping that I will be able to manually guide up to 10 mins with my 400D at around ISO800 prime focus.

Rather than have the camera do the ICNR as I have normally done up to now, I gather I should take some dark frames before hand and subtract these using either Photoshop or Registax. Is that correct?

In terms of taking darks, is it simply a case of leaving the lens cap on and taking the same exposure at the same ISO and roughly at the same temperature? Is the temperarure issue a real issue?

Some of you guys also average your darks. What is the process for doing this? e.g. can I just stack them in Registax?

Appreciate any advice guys.

John.

[JohnG]

Hi John

You have it correct, you simply take exposures of the same length, ISO, and separation as your Lights.

You can do this with the camera off the telescope and the lens cap on during setup or break down, if on the telescope and you are concerned about the temperature you simply take a few darks at the beginning, in the middle and at the end of the your sequence of Lights. Basically you are mapping the Thermal Noise of the camera.

A good article: http://www.iceinspace.com.au/index.php?id=63,211,0,0,1,0

Can't help you with PS or Registax, I use ImagesPlus 2.80, it fully automates the process.

Cheers

JohnG

[Astroman]

I have started to do this also, take darks instead of using ICNR, its alot quicker and makes the time exposing alot higher. I use Deepsky Stacker to do mine, good thing is it's free :)