Newfie Posted January 9, 2017 Share Posted January 9, 2017 (edited) After a fairly long lay off I have now managed to waterproof the observatory so I thought I would have another go at M31, although it was that long ago I think I can claim it as a first attempt. It was kind of thrown together with around 10 lights between 30 and 300 seconds and 6 darks not taken at the same time oops I know thats wrong. Anyway any advice and pointers welcome. It was taken with a 90mm ts refractor and a Canon EOS1100 modified. Edited January 10, 2017 by Newfie 6 Link to comment Share on other sites More sharing options...
gnomus Posted January 9, 2017 Share Posted January 9, 2017 Hi Newfie It is a pretty good attempt at M31 given such limited data. I like that you shot some darks. Did you shoot any bias frames? These are easy to do and you can reuse the Bias master once you've stacked it. It looks to me like you didn't shoot any flats. These are very important and may have helped with the dust spots you have and the vignetting. I would always use bias and flats. You have a bit of a gradient in there - it is green up in the top right corner and red in the bottom left. Everyone who shoots RGB images gets these gradients. Your image will improve if you can find a way to eliminate them. I use DBE in PixInsight. Others use Gradient Exterminator in PS. I haven't used Gradient Exterminator so cannot comment on it. I hope that is the sort of thing you were looking for. It is great that we can get shots like this from our back garden, isn't it? 2 Link to comment Share on other sites More sharing options...
Newfie Posted January 10, 2017 Author Share Posted January 10, 2017 No that's exactly the kind of feed back I was hoping for . No I didn't take any flats I'm just trying to work out the best way to take them nor did I take any Bias frames . I will try with both on my next attempt and thanks for the pointer towards removing the gradient I will have a look in photoshop gradient exterminator. I did notice the dust marks spots / marks at the top of the Image and wondered how best to remove them ! Again thanks very much. Link to comment Share on other sites More sharing options...
gnomus Posted January 10, 2017 Share Posted January 10, 2017 1 hour ago, Newfie said: No that's exactly the kind of feed back I was hoping for . No I didn't take any flats I'm just trying to work out the best way to take them nor did I take any Bias frames . I will try with both on my next attempt and thanks for the pointer towards removing the gradient I will have a look in photoshop gradient exterminator. I did notice the dust marks spots / marks at the top of the Image and wondered how best to remove them ! Again thanks very much. Gradient Exterminator is a Photoshop plug in: http://www.rc-astro.com/resources/GradientXTerminator/ 1 Link to comment Share on other sites More sharing options...
Horwig Posted January 10, 2017 Share Posted January 10, 2017 (edited) Hope you don't mind, I'm not claiming to be any good at processing, but love playing with images to see what's there. Anyway, this is Gradient exterminator, HLVG, with masks and layers in photoshop, I think you have a half decent M31 there with such little data. Cheers Huw Edited January 10, 2017 by Horwig 1 Link to comment Share on other sites More sharing options...
Knight of Clear Skies Posted January 10, 2017 Share Posted January 10, 2017 I'd try restacking without the darks, 6 darks aren't enough to average out properly and are likely to introduce extra noise into the image. 1 Link to comment Share on other sites More sharing options...
Newfie Posted January 10, 2017 Author Share Posted January 10, 2017 Thanks Huw for showing me a different version and it makes such a difference with it not turning green on the left of the image ! Link to comment Share on other sites More sharing options...
Newfie Posted January 10, 2017 Author Share Posted January 10, 2017 Sorry to seem like an idiot but when you suggest try stacking without the darks did you mean on my original image, and how many darks would you think I should have taken. Many thanks Link to comment Share on other sites More sharing options...
Knight of Clear Skies Posted January 10, 2017 Share Posted January 10, 2017 Just now, Newfie said: Sorry to seem like an idiot but when you suggest try stacking without the darks did you mean on my original image, and how many darks would you think I should have taken. Many thanks No problem, it's all part of the learning curve of AP. Yes, I'd suggest trying stacking just your lights and see if it comes out any better. DSLR darks can be a bit tricky, they can help but can also introduce additional noise if the temperature profile doesn't match the lights. In terms of numbers I'd think at least a dozen, with 20-30 being better if practical. The importance of darks is often overstated, personally I only take them if it's convenient. In most situations I'd prefer more lights if there is a choice between the two. Dithering (moving the aim point a few pixels between exposures) and a Kappa-Sigma clip when stacking are very effective at removing DSLR noise patterns. Hope that's some help. Link to comment Share on other sites More sharing options...
gnomus Posted January 10, 2017 Share Posted January 10, 2017 (edited) I agree with Knight. DSLR darks are awkward. They need to be at the same temperature as the lights, but even then how do you know. I go for 25. Bias frames are straightforward (and you could do them now for your M31 image). I stack 200 bias frames. Flats are important too - again I stack 25 or so. If you haven't taken the camera off your scope (you say you have an observatory) you could shoot flats now. What would also help is more subs. Less than an hour is being a bit optimistic. The joy of an observatory is that you can leave things set up and so you can have the same framing over several nights. 2-3 hours and it will start to look quite nice. 10 hours and you may get something rather special. Edited January 10, 2017 by gnomus Link to comment Share on other sites More sharing options...
Davey-T Posted January 10, 2017 Share Posted January 10, 2017 The number one thing you need to do when imaging with a DSLR is dithering the next most important thing is dithering around a dozen pixels or 2 or 3 average star diameters. Dave Link to comment Share on other sites More sharing options...
Davey-T Posted January 10, 2017 Share Posted January 10, 2017 (edited) The number one thing you need to do when imaging with a DSLR is dithering the next most important thing is dithering around a dozen pixels or 2 or 3 average star diameters. This is a crop of your background, dithering will help remove the coloured mosaic. Dave Second time today I've been unable to edit a post properly ? Edited January 10, 2017 by Davey-T Link to comment Share on other sites More sharing options...
Newfie Posted January 10, 2017 Author Share Posted January 10, 2017 Guys thanks for all the advice I was happy with the reply until I reached the last few lines "Dithering" I have never even heard this before and Kappa Sigma ! Now off to Google them so I have some idea of what they are. I do have the scope set up in an observatory so I should be able to get the darks at the correct temperature if its needed and the flats I have read so many different versions on how to take them. I have been looking at ways to do these with some form of DIY approach. One of my dogs decided to eat the cables running to the observatory and it has had a fairly serious leak so it's kind of been of of action for around a year. I am now back up and running so am looking forward to some clear nights to try your invaluable and welcome advice. Cheers Guys Link to comment Share on other sites More sharing options...
ollypenrice Posted January 10, 2017 Share Posted January 10, 2017 23 hours ago, gnomus said: Hi Newfie It is a pretty good attempt at M31 given such limited data. I like that you shot some darks. Did you shoot any bias frames? These are easy to do and you can reuse the Bias master once you've stacked it. It looks to me like you didn't shoot any flats. These are very important and may have helped with the dust spots you have and the vignetting. I would always use bias and flats. You have a bit of a gradient in there - it is green up in the top right corner and red in the bottom left. Everyone who shoots RGB images gets these gradients. Your image will improve if you can find a way to eliminate them. I use DBE in PixInsight. Others use Gradient Exterminator in PS. I haven't used Gradient Exterminator so cannot comment on it. I hope that is the sort of thing you were looking for. It is great that we can get shots like this from our back garden, isn't it? The perfect analysis. Olly Link to comment Share on other sites More sharing options...
Newfie Posted January 10, 2017 Author Share Posted January 10, 2017 As per the suggestion from Knight of clear skies I have retried without the darks let me know if it is any better made it worse, no one said anything about this been addictive ! 1 Link to comment Share on other sites More sharing options...
gnomus Posted January 10, 2017 Share Posted January 10, 2017 Second version looks much cleaner to me. Link to comment Share on other sites More sharing options...
Davey-T Posted January 10, 2017 Share Posted January 10, 2017 Are you guiding yet ? if you use PHD for guiding in combination with APT ( Astro Photography Tool ) it will take care of dithering. Dave Link to comment Share on other sites More sharing options...
MrsGnomus Posted January 10, 2017 Share Posted January 10, 2017 1 hour ago, Newfie said: One of my dogs decided to eat the cables running to the observatory You are not alone, we have also had the dog eating cables experience, Steve's write up about this appears here.. http://eapod.eu/featured-backyard-astronomer/steve-and-lis-milne/ 1 Link to comment Share on other sites More sharing options...
Horwig Posted January 10, 2017 Share Posted January 10, 2017 1 hour ago, Newfie said: no one said anything about this been addictive ! Heh Heh, it only gets worse and worse.... 1 Link to comment Share on other sites More sharing options...
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