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My M31 project (EQ3-2 unguided through an achro!)

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Hi folks. I posted up a pic of my first serious M31 attempt a few days ago. At that point i had around 143 x 30sec subs. Well I have made the most of the recent clear nights here in suffolk and attempted to catch more data, even with the moon washing out the sky. This latest stack is around 3 hours of 30sec subs at various ISO's.

Setup as per normal, ST102 achro, EQ3.2 dual motors (only RA used) Un-modded canon 500d, No filters, correctors, flatteners and all the othe fancy stuff I hear about but know nothing about lol.

4 seperate stacks in DSS, each one then stretched in PS CS2, then stacked together in DSS, and a final edit in PS, this time flipped 180*. No flats, No Bias, Just darks, stacked using kappa sigma mode.

I probably will add more data in the future, but given my setup I think I may quit whilst im ahead with this one, M31 seem a challenging target, especialy with 30sec subs! :)



Edited by stan26

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given the kit you are using the attainment of this quality is 'impossible'. superb work and proves you can get good quality images with less than very expensive kit.

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Well M31 is driving me bonkers. I took 179 30 second subs last night all at 1600 iso and they all look pretty good with nice detail in the dust lanes. I stacked them with darks flats and bias about 35 each and after ages waiting for the result I got a horriible burned out centre from the stack. I am now trying to figure out what stacking setting to use to get rid of the burned out centre so I can have something I can work with so far nothing is working. If I work on the individual subs I can get pretty nice detail but stacking them just results in a horrid mess that I cant use. Im tired going to bed now will get back with my setting to see if you can help me on this one stan ..:)

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Thanks guys.

Quatermass, let me know what settings you are using in DSS (asuming you use DSS for stacking..?) and Il try to help (bareing in mind I have only limited newbie knowledge with stacking) You could try what I did with my M51 picture, Take loads of subs, and take as many Bias frames (shortest exsposure camera will go, like 8000th sec). Set DSS to Kappa-Sigma mode to stack the lights and Median for the bias. In cosmetic section click detect hot pixels and set to 1 pixel, detection at about 90/85%. No darks, No flats. I got pretty good results using this method. My above M31 pic was stacked using these settings although I used darks.

Do you use photoshop? I could probably be a little more helpful here, because I'm quite familiar with the software. I get the same problem as you and eveyone else who image's the M31 with the burnt out core senario. It looks good to start with with 30sec subs but as you stretch out the histogram to reveal the fainter stuff the core grows getting brighter and turning to pure white as per my pic above (It will be better on my final image) However this would have been a LOT worse if I hadn't taken control of it during the editing stage. To do this I "mostly" use layers in PS. For example, Il create a duplicate bottom layer and bring the levels/curves down so that the core of the galaxy is more controlled and defined, then Il create a layer mask on the top layer and use either gradient, or brush tools and opacity to blend it in so that I get a darker less over exposed core in my main top layer image. I use this method in reverse to bring out the fainter regions as well. Then I merge or "flatten" the layers in one final image. This may not be the best way to do it, buts it works for me. BTW I understand if you don't use PS or any other advanced image editing software this last paragraph is probably all greek to you...? sorry if it is.

Hopefully some help...

Stan. :)

Edited by stan26

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That is an incredible image give the kit you used, way better than nay of my M31 attempts to date.... Thanks for sharing.


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Well Stan thanks for the heads up on what your doing. I am ok with photoshop having been using it for a year or so now my main problem is the stacking. I stacked 170 or so subs with about 30 light and darks and bias frames but when it had finished stacking I got this final image that had a really horrible burned core that was useless to do any thing with. The rest of the image was reasonable but I have not had a stacked image like this before where the core is all burned out. SO I tryed stacking again with 40 subs and no lights no bias just darks and got the same thing. Tryed again with no lights but darks and subs same problem. Went to the setting for stacking and have changed them to Kappa sigma mode in the hope that this will improve things. I didnt think you could stack a bunch and then restack the image after you stretched it but the main issue at the moment is the stacked image having a burned out core. Im not doing it all over again with my images reloaded from the camera to be sure I have not corrupted any thing I will get back to you with my results and a detailed list of my setting in deep sky stacker. Your method in photoshop is very much like mine but the stacking of the same amount of bias shots as the subs is something I have not done yet. Let me see how this next attempt comes out then I willl post again. Cheers.

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Right then, I did another stack with a fresh lot of subs from the orginals 40 subs 20 darks lights and bias. The result was this horrible thing :)


I know the subs are good but deep sky stacker is not playing ball. So here are the setting I have in deep sky stacker at present.

Under Stacking Parameters

Mosaic mode is ticked off

Align RGB in final image is ticked off

And use all processors is ticked off everything else left blank

Under Comet

Standard is ticked of and Use all processors is ticked off rest are blank.

Under Light

Kappa Sigma clipping is ticked and set at 2.00 and 5 iterations Use all processors is ticked rest are blank.

Under Dark

kappa Sigma clipping ticked

Hot pixel detection and removal ticked, Dark optimization and use all processors ticked rest left blank

Under flats and bias again sigma ticked

Under Alignment its set to automatic

Under Intermediate files

Create a calibrated file for each frame is ticked as is create a registered file and tiff the rest are left blank

Under Cosmetic

Detect and clean remaining hot pixels is ticked and set to 1pix and 72.8

and the same for detect and clean cold pixels rest are blank

Under output

Create output file ticked autosave ticked append number to blah blah ticked create output file ticked rest blank..

Ok thats all the stacking permiters

In the main window under RGB Luminance and saturation the luminance is set to 0 then 80 for darkness 10 then 33 for midtone and 0 then 50 for Highlight.

I havent got a clue why its coming up with such a horrible stacked image. Thought if I started a fresh stacked 40 subs to 20 darks flats and bias I would solve it but sadly not.

You can see from this single sub that they are not too bad at all.


Edited by Quatermass

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Ok right, This is what I use in DSS.

Under stacking parameters.


select "standard mode" leave EVERYTHING eles blank.


standard stacking



kappa set to 2.00, number of iterations set to 5.

Everything else blank.


select "median"

Tick "hot pixel detection"

everything else blank.


select median





Intermediate files:



Select both detect hot and cold pixels.

Set hot and cold filter size to 1px.

Hot detection threshold I use 83%.

Cold detection threshold 50%

Eveything else un selected


Should be ok as default settings.

In register settings, i use 10% star detection thrshold.

Try that.

By the way , what is the light pollution like in your area? Also I notice how much more light your 200p (assuming you use that for your imaging) gets compared to my little 102 frac. This is probably worth thinking about with regards to sub length/ISO/light pollution. Take a look at a 30sec ISO1600 sub from my scope. Its alot more dimmer to start with, and without a bright core. You may want to go down to ISO800...especialy if you suffer with heavy LP.....

Also I dont use DSS at all for any of the editing stretching. I simply save the file list/pic and do ALL editing in PS. I have attatched my final stack pic as shown in DSS at the end of the stacking process.

As you can see, its awful, but I'm not fussed because il edit it in PS. Have you tried going straight to PS, the final image basicaly starts off black with a few dots, not this horrible white stuff.........




Edited by stan26

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Thanks Stan, I will try again with those setting. I have just got my Canon 350d and with out a timer can only do 30 seconds max so thought I would try that. Looking at your single sub there it does indeed look much darker then mine. When I was taking these shots at 30 seconds I noticed that the light meter was completly over to the right and only when I reduced it to something like 8 seconds at ISO 1600 did it move down to the middle. Light pollution is a factor where I am, the further I turn around to the back of my house the more of it I face.

This would possibly explain why my shot of the Dumbbell Nebula gave me such good results as it was in the opposite direction away from the back of my house and the street and towards the meadows and fields where there are no lights.

Very intersesting all this just goes to show how important a dark sky is for a subject like the Andromeda Galaxy. Also tonight from about 8pm to 9pm the shots I was taking of the Andromeda Galaxy were bright with good dust lanes in the picture but by 10pm the whole picture dimmed as thin mist filled the air. To the naked eye you would not really notice it but the camera picks it up.

Well it was very cold tonight so I took a few more darks and several more bias shots to add to my collection which is building up nicely. Im sure that when I get my timer for the canon and can do longer exposures I can get much better subs for my efforts. Next time I will get in my car and find the darkest skies I can. With all the subs I have amassed on the Andromeda G. I reckon I have enough to carefully construct a much better image but all of this has made me more determined to seek out a really dark sky, several charged battery's, flasks of hot tea and the patience of a hundred saints :)

One last question then as were drifting off topic a bit. Did you stack the same amount of bias shots as you did the normal shots, as I'm going to try stacking all my shots with the same number of bias shots and see what that produces.

After that its back to Photoshop for some serious pixel punishment :)

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I think what I will do is try the stack again using your setting but given how bright my subs are and that I am gathering more light with the 200p your right that I should be using a lower ISO. Mybe the burned out sub stacks are because they are too bright in the first place. They do however have nice detail so my plan will be to batch process all the 170 or so subs I have in Photoshop by working on one sub and recording this amendments as a Photoshop action then applying this to all of them, then re stacking them again. In effect reducing there brightness and bring out more of the dust lanes so each sub is closer to the way your subs are. When you think about it, it makes sense that my stacked subs are looking so burned out now. I will let you know how I get on. Many thanks for your feed back on all this hopefully others will learn from this as well.

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Well I changed the setting in deep sky stacker as suggested there buy Stan and took only 38 subs from last night and 23 darks then stacked again this morning and went off to do some shopping. When I got back I was very pleased to see that I had a workable image and took it over to photoshop after stretching with levels and curves the applying a high pass filter and unsharp filter I finally got something that was acceptable. I have ordered myself a timer control for the Canon 350D to inable me to take longer exsposures with the bulb setting.

I have really enjoyed going back to the wonderful Andomeda Galaxy and will continue to improve on what I have managed to do so far. Many thanks for all the feed back and help this truly is a wonderful forum to be a part of I have learned a great deal and made some very good friends along the way. Heres hoping for clear skies tonight everyone :):)


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Thanks for the processing tips Stan. I struggle with the processing and thought I needed more light but now I think I need more subs and less exposure.

Really nice pic of M31.


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Thats more like it Quatermass!! :), now get some more subs and get stacking and stretching!

Thanks for comments guys, It feel's good to be able to help others.


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Cheers Stan been out tonight and taken double the subs I took last night just before the clouds rolled in as well!

Got my timer control on the way so should have some fun when that gets here and be able to get away from the camera to do some star gazing with my bins.

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