ollypenrice

Even narrowband (3 Nm Astrodon Ha) during literally full moon is useless, in my opinion. Others might disagree. Right from the start of my deep sky imaging life I've been receptive and respectful (I hope) of the findings of others but I've also wanted to find my own way forward by experimenting. I honestly think that you are the best person to answer your own question if you have both dark and moonlit data to play with. Experiment with them. I've done this with galaxy data, for instance. You have a pile of subs shot in good seeing and another pile shot in poor seeing. Do you ditch the ones from the poor seeing? Maybe not. Maybe they add to the very faint outer glows even though they detract from the nice sharp inner spiral bits. So make two stacks, the sharp data for the sharp bits and all the data for the faint bits. Then combine them selectively. I really do hate to throw anything away... Olly

The consequences of a flip collision vary from catastrophic to insignificant depending on your installation. My own mounts simply cut off when they sense an overload. An EQ6 will clack away noisily without doing itself much damage, in my experience, but seek further opinions. The other thing is that focus will drift. If you have a robotic focus then that isn't an issue. If you don't, it is. And then there's rain. You can buy rain sensing alarms easily enough so I wouldn't let that be an issue. My own situation is split down the middle. I host six entirely robotic instruments managed by their owners and I have two imaging installations of my own which are non-robotic. Essentially I'm a dinosaur... Olly

Exactly. I was trying to be brief so made no mention of the Samyang 135 lens which is doing such good stuff of late. Olly

If you've been out of astrophotography for a long time you may well be greatly over-estimating the need for aperture. Even the need for focal length has been reduced by diminishing pixel sizes. 2 metres used to be a 'galaxy' focal length. Now a metre will do fine: https://www.astrobin.com/full/omc9sk/0/ https://www.astrobin.com/full/393219/0/ https://www.astrobin.com/full/335042/0/ Two other things to note: firstly, not many chips are as big as the 35mm format film you may have used, so a metre FL will fit plenty of planetary nebulae onto modern chips but the classic emission nebulae are very large and you might find a much shorter FL, maybe 350-500mm, would suit you better. We have 530mm and 1015mm focal lengths here and the overwhelming majority of emission nebulae are shot at the shorter length. Even with a full frame chip we often do mosaics with the 530mm FL instruments. (Actually yet another thing has changed in the last twenty years: the nebulae have got bigger. Well, not really, of course, but amateur imagers are going far deeper than before and finding countless extensions and interconnections which ask for a broader field of view.) I'll just endorse what Vlaiv said, as well. The Apos tend not only to be apos but to be imaging-specific instruments with regard to field curvature, tube length and focuser design. Just in case you do go ahead with an achro for NB, the program Registar from Auriga Imaging will align and resize one image to fit another. It might cost more than the difference between the scopes, though... Olly

A mosaic will take longer but produce a larger image. Will this larger image contain more resolved details? Not if you're oversampled - as you are likely to be with a long focal length and small modern pixels. So will you make the most of the theoretically more detailed mosaic alternative? I think it unlikely if you're sampling below an arcsecond per pixel and even that might be beyond your local seeing. Do you have an idea of what it will support? I recently worked on an OSC dataset which had been stacked in APP and resampled downwards at the stacking stage. I don't know the details of the process but the data, though captured in only 90 minutes, was incredibly clean. I must say that I'd be wary of adding complexity to an already challenging RC - but that's just me! Olly

This is precisely the post I was about to make. The Hamburger is a happy hunting ground for quasars. (This was pointed out to me by Greg Parker when I posted a deep Triplet image some years ago. My thanks to him.) Olly

Interesting. My sometime neighbour is an amateur experimental archaeologist, though at a level which includes teaching PhD students from Marseille University. He makes exquisite flint tools and says, as you suggest, that pressure is the key. (Recently he came up with a widely approved explanation for the use of notched stone age mussel shells, a puzzle which had not met with a satisfying explanation prior to his.) Olly

Yessss!!!! 👏 Olly

You'll like it, I think. I doubt that you'll want to be anywhere near the bright end. I'm usually right down near the dimmest where the variable control is fairly progessive. That isn't just on my kit, either, since I periodically do flats with my robotic clients on their various rigs. I like the fact that you leave the panel securely in place knowing it won't fall off or become displaced. Olly

Just avoid the Aurora panels at all cost. The thin, rigid wires soon break. We went through three of the wretched things here, one a very large, expensive one. The Geoptik is the best I've tried. Olly

I've tried a variety of diagonals from very basic to very good and found the difference remarkably unremarkable. I'd be tempted by the clicklock because compression ring systems are a nightmare. There is no industry standard and so one EP can snag in another's diagonal or drawtube just as you are taking out. Please don't ask how I know this or whether I was a the top of the stepladdzer using a 20 inch Dob at the time... Olly

Yes, 277 meg is rather a lot! Olly

That's going really well. It's lovely and smooth and the arms will grow with more data. Olly

You're right to be pleased. Let's move straight to to the suggestions section: There's evidence of the error everyone makes at the beginning, and that's black clipping. And here's the proof: The histogram should always have a thin flat line left of the peak. If it doesn't, you have thrown away hard-won data captured at the telescope. A healthy histogram looks like this. See the flat line left of the peak. When it's black clipped it looks like this: The histogram peak is jammed up hard against the left and the background sky is jet black with the nebulosity jumping up out if it very abruptly. There is always the temptation to use black clipping to remove light pollution gradients but that is not the way forward. Olly

I did say the advantage is very target-specific and would stand by that. But, as ever, I think it's even more complicated than that. The thing about catching, say, OIII is that your filters have to pass it and your chip has to record it. That much is obvious. But what is less obvious is that, for the imager to exploit what is passed, it may also have to be isolated. A common or garden red filter will pass more or less the same amount of Ha as an Astrodon 3nm Ha filter. It isn't what the Ha filter passes which is the key to its success, it's what it blocks. So I'd throw this into the conversation: what do we do when we add Ha or OIII to RGB? I think we do this: we take an image in which the NB filter isolates particular gas emissions already present in the RGB, but we take a deeper image by exposing for longer. This allows us to stretch it harder, and LP noise is also held down by the filter to help us. (If we don't it won't show when added to the red.) The NB image has high contrasts due to its isolation of the gasses and we find ways of incorporating those high contrasts into the image. The strong signal we can add to the appropriate colour channel to brighten it but the 'exclusion zone' from the NB filter will only appear fully once the dark parts are as bright as the bright parts of the colour channel. At this point all the contrasts can be incorporated into the colour channel, though we are unlikely to achieve this. The dark parts of the NB contrasts can be inserted into the final image by being applied very slightly in luminance, for nebulae, though personally I'm reluctant to do this because it's false. Olly

This is incorrect. A mount can be perfectly polar aligned while being as far from level as is mechanically possible. The best fast-polar-alignment routine on any mount is Takahashi's and, in their system, there is no provision for levelling the mount. It sits at whatever angle the tripod places it. Try this thought experiment: Take a mount and polar align it perfectly. Next, remove the finder and insert a steel shaft through the polar axis housing and weld that shaft to supports from the observatory floor. The mount is now permanently locked in perfect alignment. Now you can loosen the locknuts used for levelling and point the pier in any direction you like and the polar alignment will remain perfect. So levelling is, ultimately, immaterial. So why do some manufacturers use it? Two reasons. 1) it sets the polar scope reticle to orthogonality with the sky (but it would have to be long way out to be discerniblly tilted anyway.) 2) It means that iterations of altitude and azimuth when using drift alignment, or variations thereof, do not interact with each other. ie An adjustment in Alt will not affect an adjustment in Az. Again this intereaction, in reality, is minor. BTW, there is precisely no reason whatever to level the mount N/S. Why would the system care about where the tilt to the equatorial angle came from? Some manufactures make equatorially tilted piers. Whatever the OP's problem is, it is does not arise from mount levelling. I agree that something in the mount must be moving. It could be primary mirror flop but, if individual subs are good, this is not quite so prime a suspect. Olly

Interestingly even some daytime photographers, paticularly in sports and wildlife, are expressing reservations about the diminishing pixel sizes at focal lengths of only 600mm or so. Olly

Your chip is APS-c sized, I think, so the flattener should cover it tolerably well. You would still be massively oversampled, though, at about 0.5 arcseconds per pixel. You'd be wanting to software bin down to about half that, since a good EQ6 under guiding cannot be expected to beat 0.5 arcsecs RMS (supporting imaging at twice that, so 1"P/P. There is no point in sampling below that.) With present technology, and notably highly sensitive cameras like yours with small pixels, an SCT strikes me as being a 'hard work solution' to the DS imaging problem. For some reason they tend to produce big stars, for one thing. My inclination would be to go for a significantly shorter focal length since you'll get the same real resolution of detail out if it, plus a wider field field of view and probably better stars. I have a 10 inch flat field SCT sitting in a cupboard but since I don't feel it is likely to beat my 1 metre FL refractor I still haven't given it an airing. Maybe I should but my present setup ain't broke... In a nutshell I think modern cameras may have put long focal lengths out of business for deep sky imaging. Olly

Just a thought but are you sure that this plate solving software can work in Alt Az? You'd really be a lot better off using it in equatorial mode for imaging. Olly

Yes, agreed, but my point is that it wasn't working for the OP who possibly didn't need it anyway. We don't know what mount he has but many can be driven to object co-ordinates on the handset, either by inputting them as user defined objects or just by looking at present RA and Dec values while slewing. When I'm imaging an object not in my mount's handset (or when I'm working on a mosaic with panels planned for various different positions) I just have the co-ordinates noted on a bit of paper and drive to them. My mounts aren't ASCOM compliant so I can't use the regular plate solving products, the plus side being that the internet and its updates cannot sabotage them! Olly

Is it really necessary to plate solve? I've done thousands of hours of imaging and have never used it. Like all things IT, it's wonderful when it works and a royal pain and unnecessary complication when it doesn't. The Rosette is very easy to identify in a finder or on a quick image because of the bright stars of the central cluster (NGC2244) which look vaguely like the 6 pattern on a domino. Olly

Really great pictures, all of which could be developed with more exp. time. I'd call this purchase a success! Nice to see a solution which doesn't involve pelting the problem with money... Olly

For visual observing I greatly prefer an alt-az mount to a German Equatorial. The Equatorial needs polar aligning and balancing and the necessary counterweights almost double the weight of the whole payload. Then, in use, the scope changes position radically between objects, the eyepiece ends up at odd angles and needs rotating, and the sky is divided into two halves requiring a meridian flip. What a palaver, even when permanently mounted! So I have always enjoyed my fork-mounted alt-az SCTs for their ease and comfort of use and fast setup. I've previously had 8 and 10 inch and now have a 14 inch. (All Meade. I have no opinion on the Meade-Celestron debate.) The 8 inch was fine to manhandle and set up. The 10 inch was not. It was 'possible' but stressful. In the end I mounted its tripod on a wooden platform or 'sled' under which I could roll a sack truck. I stored it in the garage and rolled it out as one on the sack truck, after which it was quick to align. Another alternative is the driven Dobsonian. This is just another kind of Alt-Az Go To and has to be an attractive proposition which would also lend itself to the wheeled principle. Dobs can easily have 'wheelbarrow handles' attached. A Newt, with its shorter focal length, has a much wider field of view and thus a wider range of targets than an SCT, which can leave you feeling very boxed in. I would certainly want an SCT with a 2 inch visual back so as to allow an ultra-wide two-inch EP to open things up a bit. (The focal reducer is a bit of a non-solution in that you can get the same FOV with a 2 inch EP and the view is distinctly better.) Olly

That's one of your shortest ever answers, Vlad! (But it is up there with the best of them...) Keep 'em coming! lly

I can only admire Martin's answer above, which represents exactly my own thinking as the technology evolves. Olly