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Hi All,

Having had to move to an apartment where I could not use my CPC 1100, I decided that I have to see what I could do with my NexStar SLT 102 (alt-az achromatic 102mm f6.47 refractor). Setting up on my narrow balcony was challenging and the altitude bearing was so loose that it almost moved from the weight of the Canon 700D. I could not see M31 in the estimated 3.5 magnitude sky so I did a two star alignment and used the live-view to focus on a bright star. I then took a 15 second exposure after slewing to M31 which allowed me to see that I had it in the field of view. After a few more 15 second exposures and playing with the motion controls I managed to get it centered. The resulting picture is from 39 subs of 30 seconds at ISO 1600, 9 flats. The images were stacked and stretched with Siril and then I played with the curves on Gimp, cropped and scaled. Not too unhappy.

 

r_pp_m31_stacked_stretched-RGB.png

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Very nice. You still have very dark corners. Did the flats do their job properly? 

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7 hours ago, wimvb said:

Very nice. You still have very dark corners. Did the flats do their job properly? 

Maybe the flats didn't work but I am thinking it might be due to the derotation that Siril does resulting in the corners not stacking. You can see some of this in the lower left though I tried to crop it out.

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Where's the color, did you desaturate & loose it? That's good data. I did 100 lights x 30 sec & 10 darks. 

 

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On 27/01/2020 at 15:01, Science562h said:

Where's the color, did you desaturate & loose it? That's good data. I did 100 lights x 30 sec & 10 darks. 

 

I stretched and adjusted curves separately for each channel then my mistake was to just merge down the layers for each color channel in Gimp.  Here is a version where I recomposed properly I hope - but it brought our the chromatic aberration in the stars. I am still kind of a novice when it comes to astrophotography and processing. I prefer this version because it has some color and the central bulge looks more natural, as does M32.

Cheers.

M31.png

Edited by beka
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That’s a fine result for someone new to AP. I also prefer your second version, some colour in the stars and the core is not blown out. Although bright and large, M31 is quite a tricky subject, to balance the core with the outer spiral arms, and get the colour ‘correct’ (whatever correct actually is, there is a lot of discussion on SGL on this topic.)

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I know how you feel - I have spent hours trying to get something I am really happy with.  The time I put in and the results that come out do not correlate at the moment which is compounded by the fact I know it is me that is failing and not the equipment.

But I have also learned to take what positives I can and you have a great first M31 here.  There's subtle detail and the overall shape of it is apparent.  And you've taken a photo of a ****ing galaxy from your balcony and that in itself is cool as!  Not many people can say they've done that.  I would drop the ISO down to 400 or 200 and try that as a next step.  Less noise may help tease out more detail.

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I'm starting DSO too, much fun. With GIMP, my little trick is, if I can't create a good black background to rid of light pollution, by layering & merging down, I go to "Colors," "Levels," and under All channels, I choose "Pick all black points for all channels," that's the black dropper. I then right click, what I want to clean up on the image, usually red. That gets rid of vingetting instantly. It allows for more curves. I blew out the core & colors but I got my colored spiral, that was the trade off. I do have elongation but this is a widefield test, not a best image possible.

My next test is 200 light frames x 30 sec, @ 55 mm, with an intervalometer, 20 darks & 20 bias. I'll probably throw out 40%, due to SATS, airplanes & elongation but my alt-az is good for 56%+ keepers overall. I simply have to shoot more.      

1733717157_Resizedto670x480.jpg.d7986939eff064f2471b7086d196b4c5.jpg

Image. M31 Andromeda Galaxy. Point & shoot widefield. Canon T6; 18-55mm, @ 55 mm; 50 Lights x 30 sec & 5 Darks, ISO 1600. GIMP & cropped to 670 x 480 JPEG. Celestron SLT alt-az mount. January, 2020. 

 

U see, what I did, to get color, to come out?

Edited by Science562h
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On 19/01/2020 at 17:37, beka said:

due to the derotation that Siril does resulting in the corners not stacking

Hi

Lovely shot. I like it.

Are you sure that you correctly produced a master flat frame? If you did then each light frame would have the master flat frame removed. Only then (after Siril's pre-processing) should you register -where the rotation is done- the -now flat corrected- frames. Remember also that the master bias should be removed from the flat frames before they are stacked.

Cheers and HTH

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44 minutes ago, alacant said:

Hi

Lovely shot. I like it.

Are you sure that you correctly produced a master flat frame? If you did then each light frame would have the master flat frame removed. Only then (after Siril's pre-processing) should you register -where the rotation is done- the -now flat corrected- frames. Remember also that the master bias should be removed from the flat frames before they are stacked.

Cheers and HTH

I had a master flat from some time back and it seemed to work correctly for a picture of the lagoon Lagoon Nebula I had posted then. I used the workflow on Siril so I imagine it applied the master flat to each light before the stacking and derotation. I did not take any bias or dark frames but that should probably be the next step. Another question that came to mind is, do I have to match the ISO setting on the camera for the flats and lights. If this is the case I have to do another set of flats.

Thanks for the tips.

Edited by beka
Added some more info.

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Hi Science562h,

Nice widefield image and thanks for the tips. Feels like a lifetime is required to learn and try the different features and options available in all the software packages! So what exactly does the "Pick all black points for all channels" option do to the image. Maybe one trade off is between an aesthetically pleasing image versus one in which you try not to lose any detail.

Best

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2 hours ago, beka said:

a master flat from some time back

Hi

As flat frames correct optical stuff like dust on the camera sensor, vignetting etc. they are time dependent. If you attached the camera differently or dust settled between the lagoon and the current session, then it would be best to retake the flat frames. They only take a few minutes to do. Bias similarly The 700d benefits from bias frame subtraction too. With this camera we do not use dark frames but instead dither between light frames which we find better for controlling noise.

HTH

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