almcl

it's a while since I did it, but I think you have to down load the minor planet data, in the solar system editor in plug-in, but I use very old version of Stellarium (18.2) and it may be different in more recent ones.

You can find it in Stellarium :

Yes, indeed, with the Canon 700d, luckily (and unusually) I got more than one clear night. I guess things are similar on South Island although perhaps the Otago peninsula (if you're near there) doesn't suffer as much light pollution?

One thing I found with ICE is that if it won't link all the images at the first attempt, linking just two or three and, after re-naming them so that they're in the right order, joining the new images together often worked. My 6 panel mosaic of the Rosette nebula was constructed by this method.

The effect is sometimes referred to as the keystone effect and is often noticed when tilting a camera to get tall buildings in frame (lots of web articles on the subject). Not sure of the best way to counter it in Photoshop as I don't use it, but there should be 'straighten and crop' function somewhere? Rather than Hugin, if you can find a copy, Micosoft's ICE does a better (and quicker) job, particularly with straightening things. Here's what my image editing software did to your image: The tree on the left still isn't quite vertical though.

Interesting, thanks. I'll have to investigate that a bit further?

How do you match the different flats from the various sessions to their respective lights?

ASTAP is another free alternative. It doesn't do multi session stacking properly, unlike DSS and it is mind numbingly slow (over an hour to process an image that DSS can handle in 5 minutes) but the results otherwise are OK. If you find Siril too bad (and I hate script and CLI based software) then Sirilic gets round some of the problems, although it spends ages copying files from one directory to another and then then doesn't tidy up afterwards.

I cooled my Canon 700. Not being brave enough to cut into the case for a cold finger, I applied a Peltier Cooler, heatsink and fan to the back of the camera in the space where the fold out screen sits. Although the results were not spectacular in terms of absolute cooling - it reduced the reported EXIF temp by 10 - 12°C, it did produce stable temperatures. Unlike the uncooled sessions, all the lights were within a degree of each other and, possibly more importantly, it was possible to take darks at the same temperature, something I had long given up on before clamping the arrangement to the back of the camera.

What does PHD2 report the oscillations as? Your AZEQ6 mount is capable of guiding at around .6" (or at least my 6 year old one is) and you are imaging at 2.15 " per px so even in moderate seeing should produce OK stars?

Unlikely to be dithering, as that should be taking place when the imaging camera is not taking pictures and also should be in random directions. Not sure what your set up is but if the RA and Dec oscillations are similar and you are using a guidescope it could be flexure. Hard to tell from the x4 reduced pngs, but the Rosette doesn't look as bad as the Heart?

Mine arrived in July last year and had no rubber base. I didn't realise you were visual; never used mine for visual, only imaging.

+1 for the Skywatcher model. I use it on my AZEQ6 with the SW 190MN which is quite a heavy beast and haven't noticed any stability problems. It does need the central clamps to be done up really tight to avoid disturbing the PA when slewing at speed, but have had several OAG guided sessions with PHD2 reporting average oscillation at 0.5" or just below.

If you are using Deep Sky Stacker you may need rather more lights (25+) for the Sigma Clip stacking algorithm to work. If you are guiding (not sure from your equipment list) dithering may also help, although again you need quite a few lights otherwise you get a cloud of coloured dots rather than a line.

That's not quite the case. DSS is still being developed, the latest edition is 4.2.6 and this was published in May 2021. Dave Partridge who posts here as Perdrix is maintaining the code and there is an active discussion group https://groups.io/g/DeepSkyStacker/topics

The detail in the core is just fabulous, Rodd and the strong star forming regions, emphasised by the Ha, really pop. Wonderful image as is.

You may be able to get them to stack by going to the reference frame (the one with the highest score) and manually deselecting all the hot pixels and non-stars using the star select tool. I tried this on your screen shot jpeg (never likely to be satisfactory) and got a fair number:

All shot with ASI 2600MC and Skywatcher 190MN Bubble Nebula, NGC7635 M81 NGC 7538 M106 and friends Ghost, Sh2-185

I don't think you can draw that conclusion, the drift is from 80 exposures each of 60 seconds, or 4800 seconds (80 minutes) in total and, until we know the direction of drift, it isn't possible to say if it's polar alignment, incorrect tracking speed or something else.

I think that to answer the original question we need to know what direction the drift is in. Is it along the RA axis, the Dec, or some of both? Plate solving a single sub should provide this information, but a trailed one is a bit too difficult.

The code for PHD2 is open source and although I don't really understand a word of it, the guiding stats calculations are contained in almost 700 lines of C++ here: https://github.com/OpenPHDGuiding/phd2/blob/master/guiding_stats.cpp

Many thanks for the prompt reply, Patrick! I guess APT (which is usually warming the camera at this stage) may be the culprit. I'll experiment with making CduC the last item to close.

A small but irritating problem has been apparent with Cartes du Ciel. I use it to slew the mount to target. This works well and a single plate solve, sync and re-centre usually has the target spot on. Start guiding and away we go. At the end of the session we stop guiding, shut PHD2 down, park scope and then try to disconnect and then shut down CdC. Unfortunately, no matter how I go about it, the CdC 'connect' window remains active in the task bar. The only way to get rid of it (that I have found so far) is killing it via task manager. I feel this should not be necessary? Does anyone else suffer this, admittedly fairly trivial, problem, or know a way to get it to shut down properly and close its child window in the process?

Don't think it's coma so much as tilt. Here's what ASTAP measures (28%):

Not quite. The Bias should go in the main group as they don't change, but the flats may very well be different, particularly if any dust has moved around, so you should take flats for each session and group them with the lights. You don't say what camera you are using, is it cooled? Are all the darks at the same temperature and gain or ISO? If they are, then they shouldn't vary much between nights and many re-use a 'dark library' for several months at a time. If the camera is an uncooled DSLR howeever, you may find that the darks do more harm than good and may not be at the same temperature as your lights, although experiences and individuals vary quite a bit on this.