Imaging Problem ?

[celestron8g8]

Hey everyone got a question i'm getting real puzzled about . Past Friday night i had an imaging session with my XSi and a 70-200mm f/4L . I shot 27 exposers including 12 DF exposers . I took random exposer times , few 5 , 3 , 2 & 1 min exposers and most were at f/7.1 . Afterwards i used DSS to register and stack . However in the out come i still did not have a picture worth posting . Either it's my PP or i just don't seem to know what i'm doing anymore . I've never been really good at PP but i did expect M31 to at least come out decent with the time exposers i had . All together it's over 30-45 min exposer , can't remember exactly cause i'm at work and images are at home computer . I PB this camera top my C8 on a EQ5 mount with tracking motors and probably had the best PA i've had all year . So had none or very little trailing to see . What does everyone here use for Reg & Stacking and PP with ?? Also is f/7.1 a bad idea ? My skies use to be 4.0-4.5 but now are probably 5-6 with LP . That night tho i had a moonless , perfectly clear night . So i'm really dissappointed that i can't get my Andromeda M31 to come out . Any advice here what to do or DSS ppl here ? Thanks in advance alot !

Ok here is a sample of what i'm not satisfied with .I changed it to jpeg for posting here cause i couldn't find rules for pict size . What di you think , should i be able to get more out of this or am i doing something wrong ?

EDIT : I went back and re-reg and re-stacked all images and changed a few settings in DSS and i finally was able to bring out some more however not sure exactly how it looks and it still has some gradient i can't seem to remove without clipping the black point . Whats your input and any suggestions on how to make this better ?? Thanks again !

[Euan]

You need to calm down with the acronyms it took me ages to figure out what you were saying

I would have though to get any detail in a tricky target like M31 through a camera lens you would have to shoot at 10 mins subs plus, and also faster than F7? I could be proven wrong though

Lets see it, there might be more data in there to be pulled out

[Tim]

Yep, let's see it Ron

To get the best out of M31, you need plenty of exposures, and of a reasonable length, 5 mins at least at f7.1 I should think, or longer if you can. It is difficult to get detail in the outer regions if there aren't plenty of exposures to reduce the noise.

But post up what you have, maybe it isn't so bad?

Cheers

Tim

[celestron8g8]

Sorry for the long message , just trying to set the scene . When i get home tonight i'll try posting an image up . Do you want the example from DSS or after PP in PS7 ? The core shows fair barely but the out skirts are extrmely dim to nothing . Should i shoot at f/4-f/4.5 instead of f/7.1 ? I think i shot the first at f/4 but it was almost blowed out . Not sure i kept it .

[celestron8g8]

Ok i added a new edit . Whats everyones opinion , decent , good , bad ?? Can anymore be worked out of it ?

[ollypenrice]

Why all the different exposure times? This is surely a mistake. How can you subtract the matching dark exposure if you have all these different times? All those short subs will also just add noise. I would never stack mixed exposure times myself. When the dynamic range of the target requires it I do a separate stack of shorts and layer mask them in using Photoshop.

If your tracking allows it then a minimum of five minutes will be a ball park figure, probably more like ten at f7.

For my own M31 shot at f3.9 I used 5 mins in a sensitive CCD camera. I tried short exposures for the core but did not find them useful in the end. I could get get just as deep with a less aggressive stretch of the 5 min data applied as a layer in Ps afterwards to tease out the core.

Olly

[celestron8g8]

Why all the different exposure times? This is surely a mistake. How can you subtract the matching dark exposure if you have all these different times? All those short subs will also just add noise. I would never stack mixed exposure times myself. When the dynamic range of the target requires it I do a separate stack of shorts and layer mask them in using Photoshop.

If your tracking allows it then a minimum of five minutes will be a ball park figure, probably more like ten at f7.

For my own M31 shot at f3.9 I used 5 mins in a sensitive CCD camera. I tried short exposures for the core but did not find them useful in the end. I could get get just as deep with a less aggressive stretch of the 5 min data applied as a layer in Ps afterwards to tease out the core.

Olly

I used DSS (Deep Space Stacker) for registering and stacking and according to the instructions it stacks all together properly unless i'm missing something . When i took different exposures say for examp. i took 3 5-min light frames then i would take 3 5-min dark frames and etc. with each exposure . I have heard that 1 DF for every 2 or 3 LF is a good medium . Am i not doing correctly ? I had 28 LFs' and 12 DFs' thats almost 1 for every two LFs' .

[Euan]

I have heard that 1 DF for every 2 or 3 LF is a good medium . Am i not doing correctly ? I had 28 LFs' and 12 DFs' thats almost 1 for every two LFs' .

Try and get as many dark frames as you can, and if you can at around the same temperature

[Tim]

The point is, if your light frames are 300 seconds, then your darks must be 300 seconds too. If they dont match, you might be adding noise to the image instead of reducing it. Taking random length exposures makes this very awkward to get right, better to use an intervalometer or a software program to keep to a standard length of exposure.

[Tim]

PS: the image above is more or less what can be expected for the short TOTAL exposure time. Everything is there, you just need lots more of it to start reducing the noise when you post process.

Well done

[celestron8g8]

Thanks TJ . My DF did match the same exposure length as the images . I had 5-min exposures and 5-min DF exposures and etc..... . But i had 5 , 3 , 2 & 1 minute exposures and if i had known my 5-min exposures were all turning out good i would have taken all of them at 5-mins including the DF . Next time i'll test and if i can get 5 mins ok then thats what i will shoot for .

[ollypenrice]

I like to make master darks by stacking nine or more for each exposure time. I have set point cooling but when you don't you can just make some at different temperatures and exposure times and have them in stock, so to speak. That way you don't waste imaging time.

As Tim says, you have what you could expect to have with your present run. More is never enough!

Olly