NigeB

Gav, That's a beautiful image - definitely benefiting from a very long exposure time! This is on my list of must-do targets. The first thing I think when I see your image is "wow", not "that's soft" - I don't think it is. (Have you tried some subtle deconvolution if it bothers you a lot?) A question... Have you done a side-by-side comparison of your 100ED and Edge 800 with eyepieces in the two 'scopes, so that they're both providing the same or similar magnification? I've had my TOA150 co-mounted and aligned with both my C11 and Edge 14 (not all three together!) and did that experiment - swapping quickly between two scopes on the same target. My TOA is a very good example - it's been to Es Reid who reported as much. It gives the classic refractor views, and I definitely consider myself to be a "refractor guy" with unashamed bias. But... my conclusion from that experiment was that much of what people refer to as softness in SCTs, is just a consequence of operating at such long focal lengths and large plate scales. Just my subjective opinion - I think if you did find that monster frac and imaged the same target from the same site in the same seeing as this Edge 800 image, the improvement may not be as significant as extrapolating the 100ED experience might suggest. in any case - lovely image - well done! Nigel

Thanks Rodd. I use a Tak ED 1.5 extender. It works well - optically it seems to be essentially invisible except for the desired change in plate scale, and it's lightweight (much lighter than my powermate) and has a good mechanical fit. It lives on the telescope at the moment, but I'm going to go back to f/7 for a few targets soon. Nigel

Thanks Neil. We are quite lucky, there are not many dark sky sites in the east midlands but our village is in one of the "least bad" parts for light pollution. On the negative side, I can't image planets because of trees to the south, so I have to image things high up! I'm starting to see the Pleiades creeping above the observatory wall at the end of sessions now, so some nice targets coming up to replace the Ring. Thanks Nigel

Wim, Brilliant - that is really helpful. I'd not looked at the Range Mask - that fuzziness parameter sounds like exactly the thing I was missing. Basically, I did a large scale star mask minus a small scale star mask - your method looks much more controllable. I'll give this a go and re-post when I've had a chance. Thanks Again Nigel

Thanks for your comments and link, Wim. I did use a star mask but perhaps hadn't set scale high enough - that looks like a useful repair process in the pixinsight resource. I think it's inevitable that I'll try this again. The raw data look good - it's the processing which is the issue. The lack of smooth transition between the HRDM'd core and the rest of the image is something I guess is easy to solve with layers in PS, but I'm sure there must be a way of achieving the same result in PI. One of the case studies on the PI pages is M57 taken with a 1.2 m telescope, and they also use a mask to restrict the HDRM to the core - but without the same obvious boundary. Unfortunately they don't give much detail on the process. Nigel

Evening All, I had a few good nights on M57 in the middle of the summer, but it's taken me ages to get anything remotely good out of the data. I wanted to show the outer shells, but found it was really tricky to get those to look right and still show the inner ring structure. Today I've been playing around with Pixinsight's HDRM and Deconvolution tools, with some star masks to try and protect the rest of the image. It's getting there but the detail in the central hole is not good (I can see that it's there in the data, but I've not yet managed to preserve it in the final image). You can also see quite clearly where the mask I used to restrict the HDRM processing used on the inner ring, ends. Still working on it but I need a change of subject for a while - I can see M57's with my eyes closed this evening. I think I'm more pleased with the galaxy at the 1 o'clock position than the main target...! As always, comments and suggestions very welcome - happy to let others have the stacked frames if they want to have a go. Exposure details below the image. My wife (who has been ignored all day in favour of Pixinsight) took one look at this and said "Sauron's Eye"... Thanks Nigel 16 x 600s L 16 x 600s R 10 x 600s G 10 x 600s B 13 x 1200s H-alpha TOA150 @ f/11 / Atik460 / Mesu200

Whaaaat? Poor? That's really good! Based on your title I was expecting to see a fuzzy featureless blob. I was working in Malaysia earlier this year and spent a night at an observatory with a very nice 20" RC. Jupiter was not directly overhead, but not far off. The view through the eyepiece was jaw-dropping - almost like looking at a Damien Peach image. The clarity and steadiness of the atmosphere at that elevation made all the difference and brought home what a disadvantage we have in the UK with the planets so low in the sky. Not diminishing in any way the quality of the work which people like Damien and Chris Go produce - but that clarity gives a significant head start. This is what you're up against, and I'd be very happy if I'd produced an image like yours. Nigel

My dogs are quite tall (greyhounds) and of little brain. If my other half lets them out when I'm in the observatory, they'll occasionally come in. Sometimes they just settle down on the floor, which is nice company. But occasionally they'll bump into the camera half way through an exposure. How we laugh... A long time ago when I was a kid, sitting on the green of my grandparent's village (nice dark skies), peering carefully through the eyepiece in the darkness, the local farm cat which had arrived unknown to me, jumped on my lap. I almost reached orbit. Nigel

Wow... Some great advice and suggestions here, thank you everyone. Olly, thanks for your further input. When I processed this first time around I did see some really strong dark rings around the galaxy, so I went back to the start to try and reduce that, but obviously not enough. I'll keep a closer eye on that. That's an interesting "thuggery" approach - and it looks pretty effective. I'll look at that though I don't have PS; I weighed up the software options and went for PI as my first processing splurge - maybe PS is in my future. In the mean time I'll look at GIMP to see if there's a similar approach. Neil, thanks for the Astra image pointer - I was not aware of this piece of software - looks very interesting. Dave - very useful comments; I did see the colour gradient in the stretched background though I didn't think much of it at the time since it seemed to drop below visibility after processing, but indeed, there's probably some useful information there to help track down the cause, and I missed that difference in the elongation across different colour frames. I'll need to look back at the logs and correlate the image times to see if there was a flip at that time - there certainly were flips over the nights I took the data. And it's a while since I checked alignment - it's a permanent pier mounted setup, and I use an OAG, but I've been messing about, experimenting with dual mounting telescopes and swapping them around (covered in another thread) so I'll need to give that a check. Typical - it's cloudy tonight... I'll re-post once I've done some more digging. Thanks once again. Nigel

Hi Dave, Neil, Olly, Many thanks for your positive comments - it's good to know that this is heading in the right direction and people don't find the issues too distracting. I'm going to re-process with more H-alpha and a green correction in SCNR and see how that goes - I appreciate your suggestions. Dave, I agree the elongation isn't immediately obvious. But I knew there was something amiss when I saw the subs next morning, even before I looked closely at the individual stars. The images just didn't look quite right. I get grumpy over star shapes because I know that if all is well, then in the well corrected central portion of the FOV the stars should be perfectly circular. They're a very sensitive indicator of some types of problem, like guiding, so if the stars are slightly out of circular, then that indicates a problem which is affecting the whole image, including diffuse features. Attached is a screenshot of a small portion of the stacked L frame not far from the field centre (all the stacked frames and individual subs show the same). I can see the issue in all of the stars here - the diameter in the horizontal axis is slightly, but noticeably, larger than in the vertical. To my eyes the zoomed view has a sense of minor but noticeable "motion blur" as if things were moving from left to right. So features like the dark lanes aren't as clear as they could be from this setup because I'm basically smearing out detail. Anyway: yes, please do have a go at processing this - post the results (and preferably summarise your steps - it's a great way of learning technique!) Last time I did this people told me they only used the stacked and aligned frames, not the raw subs. So I've put stacked and aligned L, R, G, B and H-alpha frames (after bias, dark and flat field correction) on my Dropbox area here: https://www.dropbox.com/sh/1kmko02tkbxqxhx/AACjT-ptgRiiVyxz7yX6nPTGa?dl=0 Let me know if you have problems accessing the files - and thanks again all. Best Regards Nigel

I stumbled into this thread out of curiosity - and now I've spent £17 on superdooper lens cleaner and a cloth. Must resist idly browsing SGL... N.

John, Many thanks for this reminder and for a great web page on Parsons and Sinden. I think I may even remember that Look North report when it went out originally - seeing Mike Neville again takes me back. I occasionally attended Newcastle Astronomical Society and some meetings at Close House when I was much younger, and met David Sinden on a couple of occasions (somewhere in my drawers I have a small fragment of glass which I acquired at one of those meetings - supposedly part of the material drilled out for the central hole in the UKIRT mirror blank). Later, long after I'd moved to Leicester, we invited him to come and give a talk to our research group. He accepted, and gave a fascinating account of his work and some of his ideas for the future - delivered with great modesty, though it was clear to everyone in the room that this was a man with not just a deep knowledge, but an innate feel, for his subject. That was not long before he died. Listening to David talking in the TV interview, it strikes me that the eloquent description he gave of Sir Howard Grubb, is every bit as fitting a description of David himself. Nigel

Neil, I only shoot LRGB at the moment (I don't bin any of my subs) so I can't comment from direct experience. There's an earlier discussion (see below) in which some opinions seem to be that, for stars and star clusters at least, RGB is just fine. My interpretation is as follows, but I'm open to correction. In L, your system is wide open to all wavelengths. Even if the throughput of your system at R+G+B is equal to the throughput of the L filter, each minute you expose at L requires at least 3 minutes (1 per R, G and B ) to match in terms of signal to noise. Since the overall signal level in an LRGB image comes from your L, and the colour information from RGB, you achieve a colour image at a given S:N quicker than you would if you were generating solely with RGB. So it may be the case that rather than saving 25% of your imaging time by dropping the L, you might be spending more imaging time than you need, by driving up your R+G+B exposure times to get good S:N, when in fact you could reduce each of those by more time than you need to add in L to achieve the same quality. I stand ready to be corrected. Regards Nigel (see other thread below)

Hi Peter, Many thanks for your comments; I'm pleased the elongation doesn't look too obvious. Once I saw it, I couldn't stop seeing it... I did wonder about wind, but it was a pretty calm sequence of nights. Good point about the extra sensitivity at F/11. I've gone back and looked at the subs again; the extent and direction of trailing seems consistent in all of them. I've checked the orientation of the long axis of the stars, and it seems to be very well aligned with the RA axis, so I'm still thinking that a poor PHD2 calibration before moving to this high Dec could be to blame. I might have another go with a forced re-calibration on something near the celestial equator and try a couple of subs on the same target to see if it behaves any differently. Thanks for the suggestion about changing the Ha balance; that's very useful feedback. It's the first time I've tried adding Ha to an LRGB image and I went with a very light touch. I'll revisit at the weekend and post an update. Best Regards Nigel