ollypenrice

Well spotted. The difference is just half a point in Ps Colour balance, midtones, away from green towards magenta. That's one point, faded by 50%. Because I wasn't confident about the background reds I reduced their colour saturation early on. Olly

In the end I decided it was in the data, though this may be wrong. It's been through DBE. There is certainly what looks like IFN in the top right. I do think the small star count might be lower in the redder regions, suggesting the presence of obscuring dust. I think when the capture is very deep it's reasonable to expect variation in the background but it's very hard to tell. I can see absolutely no trace of the green glow seen in BrendanC's image in an Equalized version of our data and have to conclude that it must be spurious. Olly

The 255 hour image on AB does show some field Ha which you might pick up. Probably worth a look, though they said it was very faint. Olly

Wow, Rivington must have livened up a bit since I last lived around there! (That would be fifty years ago...) I think the Trough of Bowland would be darker but it's further away. Olly

I was intrigued, this morning, by the feature looking like a tidal tail emerging from NGC5198, the elliptical to the right of M51. First I wanted to check that it wasn't an artifact and a careful look at the data, equalized in Ps, suggested it wasn't. I then found a couple of comparable images, including a good one by Dave Wills of PixelSkies, which also show it. Dave describes it as 'recently discovered,' as do a few other imagers who've captured it. I haven't yet found anything about the discovery but will keep looking. Yet again, the RASA shows us that 'deep is fun.' Olly

A mighty fine piece of work. We use the same lens-camera combo and, like you, find that it works! Olly

What was your image scale with the 12 inch? I'm just wondering if you were oversampled, in which case resampling downwards before processing might be good for the faint stuff. I also wonder if it might be possible to downsample still more, stretch the hell out of the tidal streams, denoiose them and then resample them back up again to blend with a conventionally processed main spiral. Thinking out loud. Olly

A huge loss. The first thing to say is that he was, quite simply, an extraordinarily nice man. He was so 'available' to the amateur community that, like many others, I met him several times and pestered him with questions which he answered with endless patience. What a very, very sad blow. Olly

RASA capture and pre-processing is, as usual, by Paul Kummer. TEC capture and all post processing is my fault! The RASA can't do high res detail with a 400mm FL but in 9 hours it can go seriously deep. This image is mostly RASA with the spiral details in M51 coming from a TEC 140 image at 0.9"PP. The RASA image was up-sampled by 25% and that's how you'll see it if you go to the full res. I think it's remarkable that we can get away with this when chasing faint tidal loops but, of course, they contain no small scale detail. Noise Xterminator is a big player in this trick. Full version is here: https://ollypenrice.smugmug.com/Other/Galaxies/i-HVknc9M/A Olly

With a large mosaic there are new problems to be overcome besides those which present themselves with a single frame image. The big ones are field geometry and field illumination. At the time we made the big Orion mosaic we were stitching in Registar and this does not generate a global template or 'cartographic projection' of the full field geometry. If you just stitch images together from one near the middle, for instance, the distortions will be crazy by the edge of the field. We had to experiment with ways of addressing this. Modern software can help with this, up to a point. We still find enormous mosaics defeat it. Software is also pretty good at seamlessly stitching two panels but, on larger scales, the brightness begins to vary so the background sky will be brighter or darker in different locations. I have worked round this by laboriously creating 'patch' sections to cover irregularities and blending them in by hand and eye. I've also worked in strips, making a strip of images across the top, then adding the neighbouring strip below that, adjusting it by hand along the way and so on down. Star removal software makes mosaics much easier but can introduce problems of its own, notably a visible tile pattern across the image. This needs a cosmetic fix if the imager can come up with one... Astronomy Now published an article in which I ran through my approach to the processing of Yves Van den Broek's Galactic Equator Mega-Mosaic. This project was easier than Orion and took about a working week. https://www.astrobin.com/full/g82xf7/B/ How long people spend on post-processing a single image, I don't know. In my case it will be about four hours then, after walking away from it, a couple more on tiny details or mild adjustments. Olly

I've collaborated with my friend Tom O'Donoghue and sold astro prints we've imaged together, though Tom did all the marketing and website construction. I won't link to his website out of respect for the forum rules, or the spirit of those rules. The image in which I collaborated had 400 hours of capture and probably a month's full time work in processing. It was also runner up in the APOTY competition. I have, though, made a satisfactory living out of astrophotography, but not by selling my images. My images have been the 'advertisements' which publicized my astronomy guest house and imaging workshops and I've also generated income by being asked by magazines to write feature articles on aspects of AP. One thing's for sure: I would not try to sell any image which did not contain something new, something not seen in any existing images. Over the last fifteen years that might leave me with about five images which meet this requirement, so not many! Sometimes I get nice messages from folks who ask if they might buy an image from me and, if the images are only mine (I do a lot of collaborations) I usually just give them away. Olly

I think there are many levels of ownership. The simplest, and weakest, is created when you buy something and it's yours. So two people go out and buy the same expensive racing bicycle and sit with it outside a café at the bottom of Mont Ventoux. One of them went out in the morning, rode up the mountain and down it, then rode over it the other way. The other just rode it from his hotel to the café. I cannot possibly consider their levels of ownership to be equivalent., though a lawyer can. Olly

Or your own remote setup? Olly

First off, it is indeed a beautiful galaxy and you've done it proud. And, secondly, it isn't available to your own observatory and that's a pretty good excuse. (When you say you'd have to get on a plane with your dual rig, I'm sure you're right. They wouldn't let you inside it with that lot! ) Unsatisfying? Hmmm... These days my 'observing,' which is to say my interaction with the night sky, comes largely through image processing. Paul Kummer looks after capture and pre-processing though, naturally, we discuss tactics ahead of that and the kit is partly mine and based at my home. Still, my situation is not entirely unlike yours with these data and yet I find it very satisfying. It's in processing its image that I feel I get to know an object. I try to tease out its secrets, persuade it to reveal things it doesn't usually reveal. This is why I now so much like working with fast systems. We can never resolve at the professional level but we can go deeper. We can also mosaic so as to show the relationship between objects and, sometimes, the way in which they are interconnected. The fast systems give me the buzz of seeing something I haven't seen before. Sometimes it's said that you never really look at something until you try to draw it. Probably true, but I'd add that I never really look at an astrophoto till I try to process it. Olly

Heretic! TeleVue rack and pinions are excellent; smooth, light and capable of holding heavy eyepieces without slipping. (This is a visual focuser, single speed.) I still have one on a 30 year old Pronto and the one on my merely 10 year old Gensis was perfect as well. Everything about the build quality of TeleVues is designed to see the scope outlive its owners. They are fully repairable and adjustable as well. I'm sure Magnus is right in that this is the F8.6. It certainly isn't one of the F5 scopes which are remarkably short, physically. (Edit: I took my F5 'Pearl River' Genesis onto a plane as carry-on.) Olly

Many thanks, Don. Olly

Never having taken solar flats I just watched a good video on how to do it. The extreme defocus method was the one I didn't understand. How can this correct vignetting if the chip is sampling a smaller or larger diameter light cone? The case for using flats is certainly overwhelming, as it is for DS imaging. Olly

A very nice, natural-looking processing job. Olly

I think you're safe. It's been so wet... Olly

What about relocating your gear to a remote hosting facility? I realize that this would leave your home observatory out of a job but not the rest of your kit. (For transparency, I do some hosting but have no availability. Places in Spain are available, though.) Olly

Don't look at a stretched version of your flat to decide. It tells you very little. What you should do is read off the ADU value of the unstretched flat (ie the linear flat) in the corners and in the middle. I've found that it was perfectly possible to ask flats to correct a 25% drop-off in brightness between centre and corners, so you need to know what your light drop-off is. It may well be that your drop-off is greater than that but, before spending, it would be worth a check. Is there any way in which you might get your filterwheel closer to the chip? You don't have any spacers between F/W and camera? Olly

None of this makes any difference if you adjust your true and final image scale at capture and then processing to what the seeing and guiding can realize. If I went for a flatfield SCT I wouldn't use the reducer, I'd capture in superpixel and/or resample before processing. This would mean I'd get the extra light per pixel onto the target and not onto background sky which I'd later crop out. Olly

The image in the link is mighty impressive. There are reds very close to, and within, the cluster which I think are ERE, Extended Red Emission, rather than Ha. UV illumination of dust produces luminescence in the 500nm to 1000nm range so it will pass through an Ha filter at around 656nm, though I guess in very small quantities. A broadband red filter will pass it far better. However, the reds on the left hand side of your image, between the pincer-like extensions from the cluster, look like Ha pure and simple. Olly

An absolute cracker of an image! The blend was certainly the right way to go - which I would say because I do that all the time. Hat's off for the Ha. The received wisdom is that there isn't any and the received wisdom is clearly wrong. You have the deep satisfaction of having brought something new to a familiar target. As for the rest, stars, background, dust, nebulosity - flawless. Take a bow! Olly

First off, it's a very clean and workmanlike image of M51. Background and stars are excellent and spiral detail is well resolved. It's very good, surely. The faint extensions are there and would show with more data. 5.5 hours has done a good job on the brighter stuff and has caught the blues in the extended tip of the 'bridge of light.' To my eye the colour balance is a tad high in green and more significantly short on red at the brighter end, though the background looks good. I'm not suggesting it's miles out, it's just where I'd be looking if the image were mine. SCTs tend to be very tolerant on reducer-to-chip distance but the true FL does vary considerably. Your variation from the nominal 1260mm is not remarkable and your intention to experiment has to be the right way, I think. While you are tinkering with this, bear in mind that all the arguments favour an OAG with this scope so it might be easier to fit one before agonizing over spacers. Regarding vignetting, I think it's to be expected on this setup. The thing is to measure it. This is easily done on flats. If you measure the centre brightness in ADU you can compare it with the corners. I found that I could live with a 25% fall-off with my Tak 106 rig so, if your uncropped corners were at 75% of centre brightness you should be OK. If your corners were darker than that you could sample the flat on a line from corner to centre and find the point at which it reached 75%. That would indicate your largest workable field. (The reality of galaxy imaging is that you rarely need a large field anyway, at least in my experience.) If I were you I'd be delighted with this as an opening result. Olly