ollypenrice

As above, where is this gradient? This is my result from a very dark site. The top left of your image is in a region of obscuring dust with little hydrogen emission while the bottom right is in a strong Ha region. What I'd concentrate on would be improving focus at capture and keeping a sharp eye on colour balance during the processing. The slightly magenta fringe around Alnitak tells you that the green is too low (green-magenta being one of the key colour axes.) Also the colour is not distinguishing between the reds of the Ha and the very unusual orange-yellow of the Flame nebula, possibly, again, because the greens are not in play. Olly

Although I wouldn't have said this a few years ago, I'd now consider a flat field SCT very seriously. The RCs are better on paper but they can be a nightmare to collimate, I suspect because of variability in the machining and mechanical side. I had a totally unsuccessful time trying to help one of my robotic clients with his and, in the end, we gave up. It did not behave as described on a wealth of different internet sources. What's changed recently lies in the processing: my objection to the SCT was its tendency to produce large stars in DS imaging but with modern star removal/replacement processing this needn't be the issue it was. The real positive is the ease with which the SCT can be collimated, thanks to its spherical primary, and the ease of long term maintenance with a sealed tube. I concur with those members above who advise against OO UK. Feel free to PM if you wish. Olly

I downloaded the files at the top of the thread but surely they are not the unprocessed linear stacks? My honest impression was that they'd been given an inappropriate stretch and some brutally invasive noise reduction. I think you need to take the data back a few steps because what you posted for download is already very badly damaged. Olly

Like Wim, I immediately thought that this did not resemble walking noise at all. The main reason for this is that it doesn't 'walk.' It's a fixed pattern, most obviously creating vertical banding but also showing horizontal banding on the same approximate pixel scale if you look closely. For me, walking noise takes the form of erroneous pixels walking across the image, almost certainly at an angle. Since this image was taken unguided it must have some inherent dither, how much depending on the polar alignment and the periodic error. The OP might try taking the first and last images of the run and stacking one on top of the other as they come from the camera. That's to say, stack them by aligning the edges of the images, not by aligning the stars. This will show the extent of the drift over the run and give an idea of the extent of the inherent dither. If it were not quite significant I'd be amazed. If the DSLR is a Canon, I think Pixinsight has a routine for 'reducing Canon banding' or something like that. I'm not sure because I don't image with a DSLR. I do know that 'Canon banding' has been identified and discussed, though. Olly

Yes, that's it. A refinement I'd be inclined to try would be doing the blue-purple halo reduction to a bottom copy layer and then activating the top layer and a feathered, bloat-sized eraser set to a partial opacity - say 50% - which I'd apply over the stars in question. You could then increase or decrease that opacity in the light of experience or use repeat iterations at 50%. This would guarantee that your bloat reduction be strictly limited to the stars you wish to alter. I make endless use of layers and opacity in Photoshop to select where, and by how much, to apply a modification. The opacity can be adjusted in several ways. 1) The global opacity of the upper layer using the layers palette slider. 2) The opacity of the eraser used to remove an unmodified top layer. 3) The Edit-Fade Eraser slider on the toolbar. A friend once said that she expected my processing to be very complicated but that all I ever did was 'use the bloody eraser!' Quite a lot of truth in that! Olly

The trick with any of the actions, or indeed any global processing alteration, is to use it as a layer and then select the opacity of the altered layer and/or use the selection tools to isolate which alterations to keep and which to erase. The Colour Select tool s very good for this. Olly

If you have Photoshop you might consider buying what we old folks still call Noel's Actions, but which is now known as Pro-digital Astronomy Tools. This is a very, very good set of actions which includes two variants of a blue-violet bloat reducing routine. It does work, as do many of the other actions which are great time savers - eg a star selection tool. You can also reduce bloated stars in Photoshop using this method: Copy Layer. Eraser, well feathered and a little larger than the bloat you want to reduce. Top layer active, take off the top layer with this eraser over the star and its bloat. You won't see anything happen because the bottom layer is still the same as the top. Bottom layer active. Curves. Place the cursor as close to the outside of the bloat as possible and alt click to put a fixing point on the background just outside the bloat. Place another fixing point on the graph below that. Now pull down the Curve above the fixing point and shape it while looking at the now-reduced star of the bottom layer. Adjust colour balance and staturation to taste and flatten. You wouldn't want to do dozens of stars like this but a few don't take long and several can be done together if they are sitting in a background of the same brightness as each other. Olly

I'm only on V6 and now just use it for stacking and calibration, but I think it's great and, as you say, blazingly fast - which really does matter in an age of short-sub, high-pixel-count CMOS cameras. My head, like yours, is done in by Pixinsight! 😁lly

The jet back sky is a dead give-away as far as black clipping goes and here we see it: I'd be inclined to take another look at the stack and keep the black point much higher so as not to lose the faint stuff. I know it's tempting to use the black point to reduce gradients but I think it's best not to do so. Love the location!!! Olly

Triplet apo, no larger than 100mm and probably less, flattener, cooled CMOS OSC and dual or tri-band filter, autoguider, EQ6, power supply, dewheater and good software. Don't forget that bit. We all like our own favourites and we should not presume to guess which ones would work best for you because we don't know how your mind works. Processing software's very personal so there's no point in my recommending what I use. You might not get on with it. Avoid extremes, as others have said. Ultra fast F ratios, very long focal lengths, very high resolution all have their plusses on paper. You won't be on paper, you'll be in a field. lly

Discussion of larger mounts for larger scopes is often overly focused on weight. A far more intractable problem is accuracy. With an eye to the future, you may want to shoot small targets like galaxies and this used to require a big scope with long focal length. It no longer does because pixels have become smaller and you can do good galaxy images with a metre or less of focal length. But... in order to shoot at fine pixel scales you still need a very high level of accuracy under guiding. Budget mounts, out of the box, cannot be counted on to deliver this. It's important to bear this in mind. Olly

If the camera can generate images by day then it must be more or less OK. The key question regarding your attempt to focus on the moon is this: once you had something recognizably moon-like on the screen, did you still have freedom to move the focuser in and out or were you close to the limit of travel in either direction? If you still had room to go either way, note that position (pencil on the draw tube) and try it on a bright star. If you couldn't move further in one of the focus directions then you might simply be out of distance. Olly

Why do you need a field rotator? I've never so much as seen one, let alone used one. If you are in focus on nearby objects but cannot focus on distant ones, your camera is too far back. (Extension tubes are needed in order to focus astronomical telescopes on nearer terrestrial targets.) However, this may not be your problem. Your best bet would be to try to focus on the moon because it's at infinity and is very bright and, therefore, unmissable. Regarding software, the less of it you introduce, the more likely you are not to have a problem with it! For initial testing, you don't need any at all besides what's in the camera and the mount's handset. Once you can focus in live view on the moon you known that the physical side of your system is working and you can plunge into the darkness of drivers and unrecognized USBs etc. Olly

Don't cameras become used when you've used them? Olly

If the optics, whatever you choose, need a flattener then I'd go for that from the start. With a DSLR-sized chip they probably will. What I would say, though, is buy from a supplier with a good attitude towards returns because optics are variable in quality. The sponsors of this site have a very good reputation in this regard. (When you come to stack images from a run you may find that distortions from a non-flattened field will have an impact on the quality of the stack even away from the edges with the distorted stars. The software can make compromises in alignment in order to align the distorted edges which adversely affect the whole image.) Olly

And perhaps more extensive? I host seven robotic setups as well as my own and camera failures so far stand at zero, if I'm not mistaken. We have a lot more trouble with mounts, though Skywatcher and Avalon are very good and Mesu are pretty well perfect. Olly

Where do you get this idea from? All my cameras are old. Not only are they old, but they have run up literally thousands of hours in commercial use. In that time (with about seven cameras) I've had one Peltier cooler fail. That's it. I bought the Atik 460 second hand and it never occurs to me to doubt that it's going to work when I go outside at night. Olly

Nonsense; there are outstandingly good used CCD cameras on the market for much less than half that, including ones with APS-c sized chips. (Anything with the Kodak 8300 chip, for instance. Atik, QSI, whatever.) And is it all that important to have an APS-c sized chip anyway? I'll link to a couple of images using the small Atik 460 CCD chip. I doubt that I'd get more than £600 for this camera but, since I'm not selling it, I don't really mind! https://www.astrobin.com/400050/ https://www.astrobin.com/6f5tfl/ Those were taken with just over a meter focal length so, of course, a shorter FL would give a wider field. As for ease, most people find the hardest part of astrophotography to be the processing. The better your data, the easier the processing. I don't think anyone is going to argue with that, but you never know! 😁lly

I only host seven of them. One's mine. Phew! 😜 Olly

Eight high-end imaging setups live here. Not a field rotator to be seen... They cant be that important! lly

I've used dual rigs for many years but always with two PCs. I think it's much easier and you don't need much of a PC, really. Just a thought. Olly

I'm going to disagree quite strongly with your opening assumptions about DSLRs. You will be using a DSLR in an environment, and for tasks, for which it was not designed. This does not make life easier, it makes it more difficult. Astro cameras, by contrast, are operating exactly as intended. They are unfamiliar and lack the external controls we are used to in regular cameras but all these controls are available in the control software. They do require a PC in the field, yes, but the PC serves other purposes on an imaging run as well and is something you might very much appreciate. If using a PC in the field is out of the question then stick with a DSLR. Dragging an imaging rig into the field is heroic and I admire those who do it. It's hard enough with a fixed observatory. However, working in your garden would become a perfectly reasonable option if you went for a monochrome camera and narrowband filters. The objects which are worth shooting at short focal lengths are mostly emission nebulae and these give great signal in Ha and OIII even from light pollution. Dusty nebulae are also nice at short focal length but require a lot of exposure time, guiding and experience, so I would leave them till later. In a nutshell, mono and narrowband would let you work from home. Note also the point made above about the need to modify DSLRs for decent sensitivity to Ha. A majority of members here will agree that it is logical to start with a DSLR. I have never taken this view and don't take it now. I've been introducing people to astrophotography for many years and think it is best to begin with kit designed for the job. Olly

Surely it cannot matter a jot? The OTA is circular in section, the accessories on the rear of the scope can be rotated to any angle... There might be an issue with locating the finder if there are no drillings but it won't be anything you can't solve. My 14 inch SCT is Meade so I don't know about the Celestron drillings. Olly

Glad to have this confirmed, Tony. The evidence pointed to the light but I found it slightly hard to believe! Olly

I switched from a small circle to something like this, Goran, but found I had to tape over the camera's little red light which was lighting up the bottom of the cable and giving a huge gradient. Olly