James, Peter has provided some very good pointers. I'm not the best person to ask since I use my own software to do this and it isn't very user friendly but there are a few things that I think are important in any software used for comet image stacking: 1) The software should stack the frames on the comet's motion by using ephemeris values for the offset rate and position angle rather than by trying to follow the motion of the comet. Astrometrica does this and I'm sure other tools do as well. As far as I know Deep Sky Stacker does not and so it's ability to stack comets is a bit hit-and-miss. 2) All the processing, including the stacking, should be done in floating point, rather than integer, arithmetic. This is very important to maximise the SNR of the resulting stack at the same time as maximising the dynamic range. This has been particularly important for this comet since the central condensation is very bright and it is important not to saturate it at the same time as bringing out the faint tail detail. Unfortunately, Astrometrica only handles integer images so it doesn't tick this box. I would hope that most modern astro image processing software uses floating point. 3) The stacking process should allow you to use a statistical method such as sigma clipping since the subframes will contain hundreds of satellite trails. This is now a fact of life for images taken low-down in twilight. DSS does do this. I've never used it but I think PixInsight would probably satisfy all three of my criteria and it is used by a lot of imagers but, again, it probably has a steep learning curve. One final thing. You often see images of comets that have been processed so that the comet and stars are both sharp. Since the comet is moving relative to the starfield this involves a software trick which uses this motion to separate the moving object (comet) from the stationary object (starfield). Each is then processed separately and the two stacks are then recombined. This works well to produce nice images but, in my view, should never be used for science images since the risk of introducing artefacts is too high. I know that this isn't really very helpful in terms of giving you actual software recommendations but other people on this list will have more direct experience of commercial software than I do. Nick. On 23/10/2024 13:02, Peter Carson wrote: > Hi James, > > The Section has its Observing Guide here:https://britastro.org/section_information_/comet-section-overview/observing-guide , which provides information on all aspects of comet observing. It doesn't have tutorials on using stacking in software—perhaps it should—but there are many good YouTube tutorials out there for many different types of image processing packages, particularly Deep Sky Stacker. > > Most of us regular comet imagers use Astrometrica to stack our images, partly because we also carry out astrometry and photometry for which the software was created. However, setting up the software is quite a task and probably not worth the time investment if you only intend to use it for the occasional comet image stack. > > Does your DSLR have a live view and a screen zoom function? These features are very useful for achieving good focus. Make sure you focus on a star, not the comet, and ensure that the star is not too bright and not saturated. A star that is just visible on the screen is probably best. If your camera doesn't have live view try a bahtinov mask. There are plenty of YouTube videos covering the use of this diffraction mask. > > After successfully stacking a comet image, further brightness and contrast adjustments will probably be necessary. Basic Deep Sky Object YouTube tutorials will provide essential advice, as Comets and Deep Sky objects are similar in this respect. > > If I can help further, you can contact me atpetercarson100@gmail.com > > Peter > > ________________________________ > From:baa-comet@simplelists.com <baa-comet@simplelists.com> on behalf ofjames@dawson.me.uk <james@dawson.me.uk> > Sent: 23 October 2024 08:58 > To:baa-comet@simplelists.com <baa-comet@simplelists.com> > Subject: RE: [BAA Comets] C/2023 A3 Tsuchishan-ATLAS this evening. > > Nick et al, > > All the images being shared are such good quality and clarity. I just can't seem to be able to process my data to look anywhere near as crisp as everyone else. > > I suspect it is because I am using a DSLR at prime focus and focus may not be spot on, but I also struggle with Deep Sky Stacker. > > Does the Section have a tutorial on stacking comet data? It would be a most valuable resource. > > Regards > > James Dawson > james@dawson.me.uk
