Most out of Cannon 450d M31

[prbirdo]

Ok I am using a Manual Guided Celestron 8SCT on a CG5 mount. I am getting best results from around 10 min exposures. But it is easier for me (and reduce stacking problems and time) to jus do long exposures.

What is the longest exposure I can get on a 450d on M31 before heating of the 450d's CCD will reduce the image quality by too much.?????

Cheers

[Uranium235]

Its not really heat/noise you need to worry about when going 20min+, its light pollution. In order to reach 20min you need a good filter, the Astronomik clip filter is pretty good for this.

But, if your guiding is good then you could probably go up to 30min. The trouble is that its going to take a million years to get a high enough number of frames at that rate. So really, the most you ever need to do is 15 or 20min. Theres no substitute for a high frame count.

Maybe you should use the 6.3 reducer too, that will help you get more light in less time.

In regard to M31, its all in the processing. Some choose to mix exposure times, or just choose one time and stick to it (eg: 20x600s). 10 min subframes should be more than adequate for M31, its a pretty bright object so overexposure wont do it any favours.

Hope that helps.

PS: Just thought, you wont be able to do M31 on a C8 anyway.... your FOV would be nowhere near big enough to fit it all in (not unless you do a mosaic). Check this out for how much of it you will actually be able to capture:

http://www.12dstring.me.uk/fov.htm

[prbirdo]

cheers, yeah i have a 6.3 reducer ( M31 tight squeeze) and astronomik filter, so more frames is more important than over all image time?

[prbirdo]

Also is the on board cannon noise reducer and high iso reducer worthwhile?

[Uranium235]

Also is the on board cannon noise reducer and high iso reducer worthwhile?

Nah, switch off noise reduction. You can shoot the dark drames (which are the ones that reduce noise) later on. Also, ISO800 should be the only setting you should use (unless doing planetary). After youve done the darks, just keep them in a stock folder so you can re-use them as much as you like (leaving more time for imaging).

The more light frames you do, the less noise there is, and you will be able to stretch the data further when processing

[Steve 1962]

Hiya

I've got a modded 1000d and an unmodded 400d and the limiting factor on both is light pollution. I'm very pleased with the CLS CCD filter which seems to allow me to go towards 30 - 35 min subs. I find iso800 better than iso 1600 from a noise perspective incidentally.

My principle is to treat the camera as "just a chip which collects light" - and I turn off everything on the camera that I can and get RAW data with as liitle interference from the camera as possible. Then you can play to your heart's content on that data on a computer .

I also agree with Uranium - take plenty of darks and multiple subs- it's a pain but well worth while.

The biggest problem I think you'll have is taking long enough exposures to get the outer arms of M31 without burning out the core, so I would suggest you take some short duration subs to get the core exposed correctly and blend them with longer duration subs to get some data from the darker, outer parts.

Hope this helps

Steve

[dph1nm]

I find iso800 better than iso 1600 from a noise perspective incidentally.

Opposite way round on my 1000D - 800 or lower is a bit of disaster zone due to structure in the read noise. For some reason it mostly vanishes at ISO1600.

Strictly speaking, there should be very little difference between ISO800 and ISO1600 as far as signal-to-noise is concerned - I believe there are measurements on the web which suggest ISO1600 has slightly lower read noise, but I think the difference may be marginal.

NigelM