Getting the best m31 picture

[willcastle]

Everyone seems to use different dslr settings for capturing andromeda! For example one person said an hour each of 2min 5min and 10min exposures at iso1600... But what will be the best number and time for exposures using a 200p? Will be getting a guidescope very shortly and will be either doing the core area or a mosaic of the whole thing! My aim is to make it a stunning picture with lots of detail! Thanks guys

[Star Gazer]

Hi Will,

I can't say what will give you the best quality image, but I would use iso 800, as anything higher brings more noise than is wanted.

Removing noise in the image processing step is not easy, at least that's what I am finding. I think the rule is to keep the noise out as much as

possible, and on an DSLR that means lower iso settings.

Anyway to help you this is what I did to get this image

Canon 7D

Megrez 72

iso 800

10 x 4 min subs

Stacked in PixInsight and tickled in Photoshop.

I think 40 (10x4) minutes is too short. I think an hour would give me a better image. Anyway I am learning too and this is my first attempt.

You can see my image has quite a bit of noise, possibly because I have pushed the curves and histogram too much to reveal the detail.

[JoLo]

Agree about the ISO, i never use 1600, pretty much stick to 800.

I finished a very nice M31 this fall (sorry, at work, no pics handy) and did 24 x 5 min exposures, plus 60 x 1 m exposures. The stacked and calibrated 1 min exposure was used as the base image, i used a mask on the overlayed 5 min stack, and managed to tone down the center of the galaxy significantly, even retained some detail. For Andromeda (and Orion) combining short exposures for the core and long ones for the detail is the way to go.

I think one hour is a minimum for strong detail in the spiral arms and the dust lanes, although StarGazer's snap is a beauty at 40 minutes, especially for a first go. I think you are right, stretching has reintroduced some noise there, although more data always helps....

[willcastle]

Wow that's fantastic for just 10 short exposures! Iv seen a picture from someone who combined six 1 hour exposures in a book before! So why do some people take really long ones and other people take no more than 5-10minute exposures at a time?

Oh and iv been reading about darks and flats... And it seems to get flats I need to take an exposure with something like a White tshirt over the end of the scope!! Do i take this at night time along with everything else? I don't see how taking a picture of a White background in the dark does anything :s

Thanks guys

[Star Gazer]

Hi willcastle,

Thanks for the complement.

The reason I took only 10 frames is because I was just feeling my way seeing what I could get in the short time I had. I'm learning how to use my kit as well, and having great fun doing so.

At the end of the day it all depends on what YOU want to achieve. I am very happy with my first attempt, but if you look at the full size original it is full of horrible noise. I know I can improve this by taking many more exposures.

Because I have so few subs there is a trade off between low apparent noise and pushing the image in processing to see the most possible detail. I decided to 'over' process the image to see as much detail in the spirals as I could. The downside is the image is very grainy with noise.

I imagine the image composed from 6 x 1 hour exposures was sublime, and could be printed A0 or greater. Sadly mine will look very grainy at A4. But you've got to start somewhere.

It will probably be next year before I revisit M31 then I will take many more subs; maybe 2 hours worth.