Disappointed M31! Any ideas?

[JKB]

So finally after weeks of cloud the sky was clear and rather that look for tiny difficult DSO's I went for something big and easy. M31. Showed up easily in the 9x50 finder and reasonably clear in the camera eyepiece. However the result is rubbish! I stuck to the settings I generally use of ISO800 Auto WB and 90s subs. I imaged M51 at the beginning of the month in similar conditions and got a half decent image.

Took 25 subs and 5 darks processed in DSS etc. After processing I had to check that it was M31.

So all you more experienced imagers: What went wrong? Not enough subs? ISO too high for the summer nights?

LP is not a problem where I live and the subs were before the moon came up!

Thanks for any help

Jamie

[Dann]

I'm not an experienced imager but I wouldn't be so hard on yourself, I think its quite good.

The core isn't burnt out and you can see the dust lanes pretty well.

[pete_l]

I did a quick (10 second) fiddle with this using GIMP to adjust the curves and there is more detail available which shows the traditional shape of the galaxy and makes M101 a bit more apparent.

You could try being a bit more aggressive when stretching the subs?

[RikM]

I would say your focus could be out a bit but mainly you just need 'loads' more subs, darks and a set of bias subtracted flats. M31 is not an easy target. You want to be looking for 60+ subs and 30 each Darks, flats and bias. If you just take your subs, darks, flats, and bias, load them all into DSS and let it sort them out. It works in a peculiar way, but gets there in the end.

I don't think it's that bad for only 25 short subs. It is a pretty low contrast object against the summer sky. If you keep adding to it through the autumn you could develop a very nice image.

[malc-c]

I assume that you used your modded webcam ? If so then that's not bad at all - I'de be pleased with that.

[RobH]

Not bad at all....don't be too hard on yourself

You've been sensible and not stretched it too far, which is nice to see.

Sorry Pete....that process is stretched way too far. Once you reach a point where noise becomes dominant, stop and pull back a bit.

One of the reasons you do have a lot of noise is that you haven't used anywhere near enough darks. Darks are like lights, the more you have of them, the less noisy the master dark is. If you use noisy darks with your image, then you end up adding noise, not getting rid of it.

You need a minimum of 25 darks, even if you only have one light!!

25 x 90s is not even 40 minutes, so don't expect too much from the fainter regions of M31.....go for a lot more subs....see if you can get a good 3 hours worth and you'll see a big difference.

Cheers

Rob

[ollypenrice]

As above, more subs and longer if you can get the guiding right. My own Andromeda got about 11 hours at f3.9. It's a long haul, getting a good image!

Olly

[Earl]

I would say you have a good starting point but need to gather lots more data.

You have to be careful with M31 as the core blows very easily.

I would consider doing to set of images one for the core and another longer set for the arms.

When its a bit higher im going to have another go at it this autum

[antimorris]

I will second(third, fourth?) the statements that you just need more data. While you will be able to see something with most images with just 1/2 hr-ish of data, many many hours are required if you want to get the detail most of us want.

Also, as mentioned, you need a LOT more darks for the noise. I know that it is tiresome if you don't have a cooled ccd to spend the time to get darks, but you really need to if you want to have a "finished" looking project.

You'll get there, just keep at it!!!

[blinky]

Nice result for 90s subs but you really should try for longer -when I last images M31 I was using 10 min subs, I would say that 5mins should be the minimum or else if you are stick with something around 90s, then you need loads of 'em.

[JKB]

Thanks all for the comments and advice. Looking forward to more clear skies and will def have more of this.

Cheers

Jamie

[JoLo]

I won't mention about additional data since others have....oops, too late! No, good shot for the amount of data you have. I find with M31 (and other galaxies / faint nebula) I am well served by backing off the stretch, but doing more of them. With a bright nebula, I can do a very agressive first stretch, then each subsequent one a bit less. On some photos, however, I find doing a series of smaller stretches works well to tease out detail without noise overpowering the image.

I also add color points to monitor the background as i stretch, add a level after each curve to reset the black point (I reset in each indvidual color channel, not RGB) and keeping an eye on the color points....I add a color balance layer in there somewhere to make adjustments as needed.

But Olly and company are correct...more data, more darks and separate integrations to keep the core in check, this will produce the beautiful M31...great job!

Joe

[ollypenrice]

While I do use short subs to layer mask onto long ones in high dynamic range images I didn't find I needed to do so with M31. I was surprized by this, but I got this far into the core with 5 minutes at F3.9.

http://ollypenrice.smugmug.com/Other/Galaxies/M31best-v1/1056334673_daDu7-X3.jpg

Olly

[RobH]

While I do use short subs to layer mask onto long ones in high dynamic range images I didn't find I needed to do so with M31.

Olly

Same here Olly.....I just find that you need to be careful when stretching it.

Rob

[Mothywood]

I will have to argue about needing over a minute exposure for a descent shot of M31. I took the image below under moderately light polluted skies which limited me to 45 second exposures. This is a combination of 33 exposures at ISO 800. Maybe it's the camera you're using? This was shot with a DSLR. Hope this helps rather than confuses.

[Mothywood]

Double post, sorry.

[pete_l]

I will have to argue about needing over a minute exposure for a descent shot of M31. I took the image below under moderately light polluted skies which limited me to 45 second exposures. This is a combination of 33 exposures at ISO 800. Maybe it's the camera you're using? This was shot with a DSLR. Hope this helps rather than confuses.

Now that's what I'd expect.

Jamie lists a 30D in the equipment list and refers to the eyepiece, so it's reasonable to assume that was the camera he used - not a webcam. He took 25 * 90 second exposures, which totals 37½ minutes of open shutter. Your image with 33 * 45 seconds comes out at 24¾ minutes.

So I'd say the problem is NOT with the number of darks, or the duration of the subs, or even the number of them. Therre does appear to be something intrinsic with the images. One thing that's happened to me (blush) more than a few times is having set the control software for X exposures of Y seconds each, to have left the camera on AUTO, or some other setting and simply not noticed - until the images come out very dark.

Jamie, is there any EXIF information with your subs? That might give some insights into what went on.