M31 subs under moon light, any point??

[stan26]

Hi folks, Was a slightly frustrating night last night, lovely and clear so I got the 102 out for an obb's session, let it cool down went out and then it suddenly occured to me that any target of possible interest was going to be washed out by the moon light. To add to that my house is 10yds east of my pier so I couldn't even observe the moon or jupiter untill very late (work the next morning). So I though sod it, swung on to M31 snapped the DSLR on a set it off taking 30sec subs. I found that the outer structure was very faint with the moon lit sky glow in my individual subs, but I carried on anyway.....

My question is, should I add these subs to my current M31 stacks?? or am I wasting my time? will it decrease the quality of the final image, or could it help to add detail? Don't get me wrong, they're not badly washed out image's, just have a blue hue as opposed to a nice inky black sky. Because I use and unguided EQ3-2 I need to get as many subs as possible, taking evey opportunity I can to grab some more data.....

Cheers

Stan:icon_confused:

[stan26]

Just had a play with the individual subs from different nights, one with moon, one without, with very simular editing (stretching histo) in PS with both of them. The 2 pics attatched are both ISO1600 30sec exposures. Interesting that the "darker" less noisey one is actually the moonlit version. Its obvious that theres more detail in the "no moon" version though....

Hmm, I think il give it ago and stack them in.....

[Earl]

With the moon out to play, its either Narrowband or image the moon / planets.

[JohnnyD333]

It is difficult to image with a full moon, however, your second image looks like a vignetting issue. Have you added any flats to it? It could help, but I do agree that the moon makes things very tricky and if you cant fix that image with a flat you may want to avoid stacking it with your others.

[stan26]

Its the data/detail i can capture in a single sub that im interested in. The above pics have been stretched out to show that. No flats or darks needed for this simple exercise if you get me.....?

This is what i have so far. This is the result of 143 x of the above left hand subs.

http://stargazerslounge.com/imaging-deep-sky/158797-my-first-attempt-m31-unguided-eq3-2-a.html

Im wondering if i should add 100 or so of the right hand (moonlit) versions......

Stan.

[JohnnyD333]

I got ya, your first attempt in the link is quite a nice image. All I can say now is experiment because you have some data in those images but the brightness/vignetting/moonlight might ruin the excellent pic you have already. Good luck and let us know how you do:)

[Salvino]

I think if you use a 7nm hydrogen alpha filter will fix that problem of moon glow

Sal

[Quatermass]

Interesting.. are you stretching individual subs then stacking them or just playing around with individual subs and stacking all of them when you have played around with one? I tried out my canon 350d tonight and noticed I had a fair bit of detail in a 30 second sub at 1600 ISO maybe I just need more of them as I only had 41 subs bit didn't take enough care balancing my scope out and they all had star trails grrr frustrating that as it was really cold tonight still live and learn. Are they all just 30 seconds at 1600 iso? if so that would be useful as I dont have bulb timer remote yet, well I have one but its for my other camera and wont work on the canon so have to get another one for it. In the mean time I can start collecting short subs of 30seconds. Can you do that.. stack subs you have stretched all ready or is there no point in doing that slightly confused...

[stan26]

Interesting.. are you stretching individual subs then stacking them or just playing around with individual subs and stacking all of them when you have played around with one? I tried out my canon 350d tonight and noticed I had a fair bit of detail in a 30 second sub at 1600 ISO maybe I just need more of them as I only had 41 subs bit didn't take enough care balancing my scope out and they all had star trails grrr frustrating that as it was really cold tonight still live and learn. Are they all just 30 seconds at 1600 iso? if so that would be useful as I dont have bulb timer remote yet, well I have one but its for my other camera and wont work on the canon so have to get another one for it. In the mean time I can start collecting short subs of 30seconds. Can you do that.. stack subs you have stretched all ready or is there no point in doing that slightly confused...

I never pre-edit any subs. This would be very time consuming and I guess pointless considering that the data contained within each sub is retained within the final stacked image, even if the final stacked image is black with a few white dots and a fuzzy thing in the middle, it still contains all of that data captured in each sub (at least this is how i understand it) I only stretched the above two individual subs to get an idea of how/if the moon was having much affect on the data the camera was capturing, beacuse its sometimes hard to judge what we have by just looking at the images on the camera screen, and the histogram of the CR2 (raw file) on the camera will naturaly show the data squashed up in the left quarter, so no way of judging by looking at that either. The above images are ISO1600, the M31 stacked/processed pic that I done (in the link) also had a few ISO3200 subs chucked in to help bring out the fainter stuff (only with no moon). I find ISO1600 adequate for most stuff. I can go to 1min exposures and have had the odd 1.5min with the EQ3-2, I stick to 30sec subs so that I have more keepers. now I have my mount on a pier and the polar alignment is spot on, I find that I get upto 75% keepers with only periodic error forcing me to ditch the rest. Get urself a timer remote. I got mine for about £12 on amazon, I find it absolutely essential for imaging, just set the sub length, number of subs you want to take and hit the go button, done! go back in the warm and sit on SGL, or grab another scope to do some obbs. Return to the camera an hour later to find you have taken 120x star trailed pics because you forgot to swich the motor drive on

BTW with regards to balancing the scope, Set it up so that its slightly heavier on the side thats been pulled up through the east side so that it loads the motor, If its perfectly balanced through the RA you'll get wobbly stars because the load will canstantly be shifting on the balance point,....if that make sense (sorry if you already knew this btw)

Stan.

[Quatermass]

Thanks Stan its was a rush job last night and those subs I took were rubbish because It looked like they were sharp in the small lcd screen of the canon 350d compared to my lush live view on the Lumix G1. When I sussed out the zoom feature to view the image that made me feel better. At least I can now double check that my polar alignment is OK and I'm getting no trialing. I have imaged several targets that required good tracking and done OK in the past so wont have any problems now I know how to inspect the shots I have taken on the cameras display. Need an observatory shed sigh.

[rocketandroll]

I had a similar issue with my M31 shot recently.

I had a 45 minute set of beautiful clear subs taken at Kelling, I then took another hour and a quarter or so the following week during all that haze.

The only way I could get a decent result was to stack each set separately, do a levels stretch on each finished image, then stack the two 16bit images together.

Stacking the whole lot together in one go produced the most ghastly result :-(

Ben

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[ollypenrice]

Personally I wouldn't shoot anything but Ha in significant moonlight. I think what's happening is that the fullish spectrum reflected by the moon is swamping your light pollution, that's all. However, the faint detail you want to capture still has to climb above that background level.

I suspect that the moonlit images will just add noise but, as ever, the thing is to try with and without. I do this when I have indifferent data due to haze or whatever. Just try it and see.

Olly