ollypenrice

The terminology is bad enough without some maniac coining the term 'Dark flat frames!!!' 👹 For heaven's sake, dark is an adjective and flat is a noun in this sentence. A flat cannot, under any circumstances, be described as 'dark.' At least, 'Flat dark' can reasonably be taken to mean 'Dark for flats' and that is the term I would rather see used. But please spare us from 'Dark flats.' No wonder newcomers get this round their necks. Olly

Astrodon filters are 3mm thick and Baaders 2mm. 1mm strikes me as being unlikely... Olly

Indeed, and that could easily include Betelgeuse right now... Olly

I think that, although it will be very bright as seen from the Earth, it will still be a point source and won't have anything like the illuminating power of the sun. In my understanding it will look like a very bright star, or something more like Venus, perhaps. It won't turn night into day. If humans are still around to see it, and I wouldn't bank on that, perhaps they'll name its remains The Betelgeuse Nebula? Interestingly, the Crab Nebula and Betelgeuse are at similar distances but I'm not sure how much is known about the Crab's progenitor star. It seems that the science on this is evolving, with the possibility that the supernova was of a new kind - or new to science, that is. Olly

Yes, any tilt in the focuser needs eliminating before using a star test. Actually I've had a refractor here for some time which needs the front cell adjusting and I've always assumed I'd get round to it using the method from TeleVue. Olly

Do you need a laser? Some years ago I phoned TeleVue in the States because I had a scope of theirs which was giving shuttlecock stars inside and outside focus after it had been bumped. The scope had, like the OP's, a front lens cell but it wasn't held in alignment by three pairs of antagonistic screws along the optical axis but by three radial screws. I was advised to loosen the three screws, move the lens cell with my fingers and stop when I had concentric diffraction circles out of focus. This proved remarkably easy. At this point the advice was to tighten the three radial screws very gently, a little at a time, while ensuring that the concentric circles were not disturbed. This procedure worked and when I later imaged with the scope (which was intended only for visual) it gave round stars. I'd be inclined to try this using an illuminated ball bearing as the time-honoured artifical star, but using the antagoniostic screws to adjust the cell. Olly

Agreed. At one times this mania for for short tubes was a William Optics speciality but the malady has spread... Olly

I'd suggest ditching the Ha and putting the time into broadband. Barnard's loop, strong in Ha, is really out of shot here and I don't see the Ha having made much of a contribution. It strikes me that you have everything in place bar sufficient data. The processing looks very good and on a target with trickily high dynamic range. Olly

I think it's great and also that Valiv's critique was dead right. I always use noise reduction reluctantly and only ever on parts of the image which need it. Invariably these are regions of low signal which have also been given the hardest stretch. I'd probably let the stars be a touch softer, too. You don't wnat them to poke the viewer in the eye! 😁 We don't often see images of this quality from a beginner, that's for sure. Olly

Spot on. I always insist that the first key skill to learn is how to look at your image or, rather, how to see it. What needs to be done is always right there in front of you, but first you have to see it. As a beginner, and even as an experienced imager, this can be harder than you might think. Indeed, I still don't trust my own judgement on the background sky after many years of imaging and always measure it to make sure its values are equal in red, green and blue and to be sure that it's not getting too dark. (Too light's not a problem and can be fixed as the final operation.) Olly

Stacking and calibrating is a mechanical and essentially mundane process which can be handled by all the dedicated packages listed in this thread. The really important first steps in post processing are gradient removal and colour calibration, which are related to each other. Be sure only to choose a package which can do these things easily and well. Everything you go on to do in post processing is predicated upon those two first steps and, if they are not done well, will lead you into irreparable processing errors. Time and again we see beginners posting images which have been black clipped in order to remove residual gradients, meaning their faint data have been discarded and only starting again can restore them. Personally I use Pixinsight's Dynamic Background Extraction or Automatic Background Extraction for this but I do little else in Pixinsight. It's a powerful program but it's willfully obscure and isn't somewhere I like to spend my processing time. Astro Art's gradient removal isn't bad and I get the impression that APP's is very good indeed. I'll leave it to others to comment on their favourites - but make this your first priority. Adobe's business model has made Photoshop public enemy number one for many people but I do most of my processing in there. It has risen to its celebrated position for good reasons and lets me use layers and selection tools in a 'touchy-feely' kind of way while seeing in real time what effects an intervention has. Others prefer to work differently in different programs. Beware of U-tube tutorials, many of which are exercises in aimless floundering! The moment you hear the perpetrator say, 'I just play around with these sliders till I like what I see,' switch them off and delete them from your hard drive. As you learn processing, make it a rule never to use any intervention you don't understand. Work out what it's doing to the data and think it through. Begin by being crystal clear on what's going on in the histogram, in levels and in curves (or whatever name these are given in your program.) This 'stretching' is what it's all about in AP. And, finally, remember that few processes should be applied to the whole image. Sharpening, noise reduction, adjustment in colour intensity, etc. etc. need to be done selectively to different parts of the image. This is so blissfully easy in Photoshop (and maybe in its cheaper or free imitators.) Olly

Is the problem one of identifying critical focus or of moving the focus ring with sufficient sensitivity to find and sustain it? Or is it both? Telescope Service do this gadget but it would be easy to improvise something along the same lines. All you need is a ring with a protrusion from it fastened round the focus ring. The protrusion is pushed by a bolt at right angles to it. In the device above there is an opposed bolt to push the protrusion the other way but it might be easier to dispense with this and have a spring or rubber band pushing or pulling the protrusion up against the bolt. I used a spring on my very effective Tak microfocuser. Once you have fine control like this, the 'vanishing small stars test' is probably as good as any. Olly

The test would be to look at the relationship between sub quality and guide trace. Flexure between guide scope and main scope can give a sound trace but a defective image. Olly

But the mounts will produce the same errors however they are guided, no? Olly

Exactly what I find as well. Olly

In principle an OAG is the right choice for a reflector because mirror movement is always possible and its effects are corrected by an OAG but not by a guidescope. They have to fit, though, and since we're using a RASA 8 at the moment, they won't in our case. Regarding expensive astro-bracketery, I agree with Alacant on this. Just make your own. If you are struggling to cut thicker alloy plate you can simply epoxy two or three layers of thinner sheet together and you'll get all the rigidity you need. Home made bits and bobs abound in our observatories. They're not trying to win a beauty contest (which is just as well! ) Olly

Before changing anything you can simply look at your guide RMS to see how your guiding matches up with your imaging pixel scale. This requires your guider to be told the FL of your guide scope and the size of your guide cam pixels. If your guide software can't give you this, switch to PHD2 which can. The rule of thumb is that the RMS should be about half the image scale. But here's the thing: if you are getting some good subs and some bad ones, changing your guider is unlikely to cure this. On the bad subs, something has clearly defeated the guider. The same 'something' will, in all probablity, defeat any guider. Optimizing the guider is not really going to be about getting the infamous round stars, it will be about getting smaller stars and better resolution everywhere. Most of us have experience of using a perfectly matched autoguider which did not give optimal guiding. I think that you are in danger of joining this club if you don't get to the bottom of your present problem! Olly

Yes, fair point. Olly

Sure, but this happens remarkably rarely, I find. We often see M31 framed on the diagonal but this is usually a shame because, most of the time at telescopic focal lengths, it needs a two panel to fit in it's full glow. When we 'squeeze things in' we often miss their full glory because, the more data we collect, the bigger they become! That's part of the buzz, of course.

Swapping filters between subs strikes me as a little pointless in narrowband, but I may be missing something? I can see why you'd do it in R,G and B because you need about the same number of each and being short on one is useless. More would always be nice but slightly too few, provided you have the same number of each, can give you an image. It's different in NB. You are always going to need a lot and you don't need the same number of each, so shooting one set then another makes sense. It makes even more sense if you use somewhat moonlit nights for the Ha. Do you need the same make of Ha and OIII? Depends on what you're going to do with the subs. If you're going to add the data to (L)RGB then you don't. The main difference will be in star size and you won't be including the stars in the LRGB data. If your project is NB-only then I guess you really do need the same filters to get a good match on the stars. Astrodon NB filters are stunning, as they should be. I've processed their RGB data as well and, quite honestly, I don't think it's that different from Baader data. So... fancy NB filters, yes. Fancy LRGB, not so important. Olly

Have you seen the film, The Dish? It's an entertaining film and highly relevant to this conversation... 👹lly

I just go for 'landscape' or 'portrait' relative to RA and Dec. That makes it dead easy to add data in years to come. Olly

An Atik 11000 mono, HaLRGB. Olly

Following a discussion on the widefield thread, I tried a blend of RASA and FSQ data where I had overlap. Here we go: Olly

Honestly, you clean a corrector by just cleaning it. There is no mystery to it. You can use a lint-free cloth and Baader fluid, wipe in curves and don't re-use the same bit of the cloth per wipe. To remind yourself of the reality of 'stuff on the corrector,' take a look at the middle of it. What do you see? An enormous great secondary mirror. And does this ruin the image? Because the primary is spherical it is easy to collimate just using the manual's method. Just move the adustment screws in small increments. Relax! Olly