New to imaging, is this amp glow?

[big bedroom]

Hi. This is my first serious attempt at imaging. It's a stack of 36 x 30 second subs taken with my sony a700 prime focus on a celestron F5 wide view, with a skywatcher light pollution filter. My tracking wasn't spot on, getting to grips with my first eq mount too!, and m31 moved upwards by around an inch over the course of the session.

It was just lights, no darks. And the subs were jpegs as my ancient laptop wouldn't handle that many raw files.

As you can see it has a lighter patch covering most of the lower middle of the image. Is this amp glow? Or just my bad processing? I used deep sky stacker, and tweaked it using the tools in the software to highlight the patch which gets bigger as I try to bring out the galaxy.

It shows in the single subs but only if I tweak the contrast.

[ronin]

No idea others may have but did you cover the rear view finder of the camera? That lets light in.

Also did you allow the camera to take noise reduction exposures after each normal exposure?

On a Sony anything over a second the camera will try to do a noise reduction exposure of the same duration - it may have been disabled, but it is relevant. The noise reduxtion exposure is in effect a simple dark which the camera subtracts from the normal.

[big bedroom]

Ah! The view finder, I'd never thought of that. I'll have to try covering it next clear night. High ISO NR was on but long exposure NR was off. I was at ISO 800 and the camera was processing a long time after each sub.

Cheers ronin.

[Marky1973]

Hi, I am no expert either as I am just starting out, but I reckon you will get better results if you start adding in the DARK/FLATS/BIAS shots - Darks and Bias are relatively easy, and I have been using my Flower Pot method for flats.

If you check out this link you can see the effects of including flats and not including them - without them I was getting similar effect to you when stacked and processing. I am sure my skills with GIMP probably didn't help, but the flats certainly improved the image.

I am sure some more experienced imagers will give you a better solution, but worth a try! And regardless of the effect, it is still a nice first effort as you can make out the dust clouds - it gives you a great feeling doesn't it!

[Blazar]

Hi. good first image. Looks like it might be over processed, in addition to the fact that they were Jpegs. I did a similar thing to show a friend that his stack did have data in it, and it had a similar halo (IE hard processing and stretching). 

So this was the image stretched:

So the same dark line at the bottom of the image etc. 

The thread and  subsequent re-processing by Knobby is here, and has some links to resources that helped him. He ended up with a very nice first unguided image.

Not done too much in the way of DSO stuff, but did do an M31 and only used 10 x 30 second with Darks...they do make a difference. my second attempt was much better, though still a long way to go!

Keep at it....its a marathon, not a sprint ;-)

[Chris]

It looks very much like vignetting which is then been stretched in post processing. You need to take flat frames specifically, these will subtract vignetting. Dark frames will subtract noise. I've not done Flats for a while but I used to do it this way at the end of my imaging runs:

1) stretch a doubled up white T-shirt over the aperture of the scope and secure with an elastic band (works best of small scopes).

2) shine a torch on the T-shirt from such a distance that it evenly illuminates the part of the T-shirt covering the aperture.

3) whilst shining the torch take different lengths of very short exposures until the image displayed looks like a light grey card.

4) once the correct exposure is found take a number of exposures at this exposure length

5) load them into the 'Flats' tab in DSS along with your lights and darks etc.

Like I say its been a while since I've done them but when I was imaging alot I certainly paid the price when I didn't do them. 

They are more important than darks if you ask me.

[ollypenrice]

Yes, you just need to take flats (which I think you are calling 'lights' in your post, but lights are the images of the object itself, in the language of imaging.) What you have is vignetting, not amp glow.

Olly

[big bedroom]

Thanks for the help people, good to know my old camera is ok. Now just got to work on darks and flats, never done this before and it seems like a "dark art"! Hopefully there'll be some clear weather and I can have another crack at it this weekend.

[big bedroom]

Hi, I am no expert either as I am just starting out, but I reckon you will get better results if you start adding in the DARK/FLATS/BIAS shots - Darks and Bias are relatively easy, and I have been using my Flower Pot method for flats.

If you check out this link you can see the effects of including flats and not including them - without them I was getting similar effect to you when stacked and processing. I am sure my skills with GIMP probably didn't help, but the flats certainly improved the image.

I am sure some more experienced imagers will give you a better solution, but worth a try! And regardless of the effect, it is still a nice first effort as you can make out the dust clouds - it gives you a great feeling doesn't it!

That flowerpot looks a good idea, thanks Marky.

I know, I'm hooked! I did have a try at Pleiades but with an F5 achro the results weren't great!