ollypenrice

A Star Adventurer mount with camera and lens would be a good way to start. You can use a basic second hand prime lens with advantage provided you can source an adapter to use it with your camera. You don't need autofocus compatibility. Olly

I agree, I think focus may have been a little soft. I think the hardness in Rustang's image may be from global sharpening? Olly

This looks good. The stars look a bit hard, though, a bit too sharp. I always exclude stars when sharpening. Very easy with Noel's Actions. Use 'Select brighter stars,' expand and feather considerably and the select inverse in Ps. Sharpen that. I always sharpen a bottom layer with the original on top so I can use the eraser to let the sharpening through, paritally or fully, only where I want it. Olly Edit. Indeed, when very undersampled, as with my old Atik 4000 and focally-reduced Tak FSQ, I would sometimes select the stars and blur them to loose a slightly 'blocky' look.

These are not credible flats. The patterns of light and dark cannot possibly be created, as they should be, by collecting light as the telescope collects it and the camera records it. Something else is getting in there and creating the patterns we see, so we need to know everything about every light source ending photons onto your chip. That means a precise description of your method, including any sources of ambient light. Olly

A tip regarding Local Contrast Enhance: it pushes the darks down and the lights up, not unreasonably given its name, but that means you need a high black point to run it or it will black clip and bring the darks down too far. Bear that in mind. Even when you have a high black point, as I did when I ran it, it pushed the darks down too far. Not to worry: apply it 'As Layer on top' which is an action in the list, and then, in the Layers menu, change the blend mode to Lighten. When you do that, the darkening aspect of Local Contrast Enhance will be ignored and only the lightening aspects applied. You can then run it again and try the normal blend mode or give it a second dose of Lighten, as you wish. And a tip regarding DSS: ditch it and use something else! I do my stacking and calibrating in AstroArt. I had no black stellar cores when I opened your data in Pixinsight. Because I like working in Ps I exported the file as a 16 bit TIFF. Olly

Nice. Just some black stellar cores (from masking?) Olly

Thanks. This is processed for contrast, since that's the topic. It's not necessarily what I'd do 'for real.' I haven't edge cropped it and this is full size so JPEG losses. Olly

This is, with absolutely no doubt whatever, a processing issue. It has nothing to do with capture. Others have demonstrated the potential for higher contrast contained in the data. However, we can point you towards the processing techniques which will enhance both global and local contrasts but the extent to which you apply them will remain your call. Many images strike me as over-processed in the way Craig T82 describes above. So I'll give you a couple of ways to enhance contrast but don't take that as my saying you should use them. Make your own picture. Wim has covered the black point so let's look at... The stretch: When we stretch an image we do so non-linearly, so we stretch the dark parts by far more than the light parts, so increasing contrast in the dark parts. That's how we extract the nebulosity from the background. However, different stretches will give different levels of contrast. If you stretch in Levels you'll get a logarithmic stretch which looks something like this when seen in Curves: This is a gentle curve and the difference in stretch between the red and blue lines shows the difference in stretch between those points. This will give a natural looking image with moderate contrasts. The alternative is an aggressive stretch.: Here all the contrasts between dark and moderate signal have been massively increased. Note the difference in stretch between red and blue. That difference is contrast. I've shown this stretch before on here and it has raised eyebrows and disapproval but it remains one of my go-to operations, above all in narrowband where its increase of star size is not such an issue. When I demo these curves on this data with guests, most prefer the hard stretch. It was the stretch used in the Ha and OIII of this final version: https://www.astrobin.com/327970/ If you use Photoshop consider Noel's Actions (now called Pro Digital Astronomy Tools) which has an excellent routine called Local Contrast Enhancement. In Pixinsight try Local Contrast Equalization (which you can also replicate in Photoshop.) Olly

That is very persuasive! Thanks, Olly

Thanks very much indeed for taking the trouble. Much appreciated. We would probably go for a similar camera. I'll work with 700mm. You're right! This is a potential joint venture and would be fully robotic, but compatibility with the shed has to be a first thing to verify. Placing an extra weight well forward of the normal point of balance does give some leeway for sliding the tube downwards but we need to be sure the thing would fit. SGL as incomparable as ever. Thanks all. Olly

If anyone knows it, I'd like to learn the distance from the middle of the saddle plate to the very front of the camera once the setup is balanced. It's possible to look up the length of the OTA and the camera and add them together to get the full length of the system but what is critical for us is the extent to which the camera extends forward of the centre of the saddle plate. (This is because it needs to fit in an existing roll-off with no possibility whatever of collision with the roof. Roof hits camera, shatters corrector and the bits drop onto the primary... Let's change the subject!!! So it's the indicated distance in this picture from the point of balance in Dec to the front of camera. If you could also give your model of camera or the distance from the end of the OTA to the very front of your camera that would also be great. I know it's a rare beast. Thanks, Olly

I had a quick look but apologize if I missed it. Olly

This is not good at all. What's the story, here? https://www.bbc.com/news/uk-scotland-south-scotland-57579980?fbclid=IwAR2o4UH7YqPEhI0np236xT7LpKnSjcahpWpfhyjGeonrrBUaOqR5KBaAgwI Olly

I've had Esprits visit and produce fine results but can't help compare the Meade 127 with the Esprit. However, I can compare the 127 with the TEC140 since I had the 127 and now have a 140 and also use another example. The big difference is in star quality. My Meade bloated quite significantly in blue and, by not focusing all wavelengths so accurately, gave unpredictable star colour. I'm sure the Esprit will show the same advantages over the 127. Olly

You have to define 'use.' The 'use' of a spanner is to loosen a nut. What is the 'use' of loosening a nut? Loosening a nut is useful to remove a wheel. What is the 'use' of removing a wheel? To repair a puncture. What is the use of repairing a puncture? It gets you to the next town. What is the use of getting to the next town? It has a shop which sells spanners. What is the use of a spanner? It will let me remove a different nut. What is the use of removing a different nut? It will let me remove the radiator. What is the use of removing the radiator? It will let me repair the radiator to get to the town if the radiator fails... And so we go round in circles. Astronomy is different. It has no use. It is an end in itself. Either you want to understand a little more about our place in nature or you don't. If you don't, forget astronomy and add to your collection of useful spanners. Olly

My first experiment would be to shoot mono luminance at the lower resolution and than take both that, and the higher res OSC, into Registar and ask Registar to resize the OSC downwards to match the luminance. Given the downsizing of the the OSC which will follow, and the greater sensitivity of the OSC CMOS camera, I suspect that this might give you all you need. I would only look for a more complicated solution if it didn't. If this is dual rig data you have, in effect, a 'given' in that you'll be shooting equal amounts in both cameras with no sensible way of doing otherwise. What I am suggesting is predicated on the higher sensitivity of the CMOS (OSC) over the mono CCD. Shooting OSC and luminance in equal amounts with comparable cameras will not, in my experience and that of others I know, produce an adequate colour layer. We all know from experience that you need an awful lot more data to present an image at 100% over, say, 66%. This holds true even if you're not using a more sophisticated downsizing algorithm. How much difference the algorithm makes, however, I don't know. Olly

I used to image with Yves van den Broek's 14 inch ODK at 0.62"PP. A kit shuffle here saw me switch to a TEC 140 at 0.9"PP with an Atik 460. Personally I find little to choose between the results. I did a back to back on here a while ago and some members felt the big scope sometimes captured more useful detail. Personally I found precious little to choose and preferred the rafractor stars to the spiked ones. One or two targets ware very difficult on the big one due to out of shot beams from bright stars. The obvious thing to try would have been binning 2x2 but the SX H36 would not bin satisfactorily. (Dark triangular artifacts next to stellar cores even after electronic adjustment.) I'll link to some results from the TEC so you can decide what you make of them. https://www.astrobin.com/omc9sk/ https://www.astrobin.com/full/6f5tfl/0/ https://www.astrobin.com/full/419975/0/ https://www.astrobin.com/full/miqpyu/0/ https://www.astrobin.com/full/393219/0/ Since I have so many instruments on site now I really don't much care for tinkering and like the plug and play way of imaging with a large refractor. However, you're rather an expert at getting the best out of tricky stuff and might enjoy that aspect. We all know that, in the end, a big scope will win but as amateurs in the real world I'm not sure that we are anywhere near 'the end' in question! Olly

Yes, I'm sure it does. A recent head of Fermilab didn't believe in dark enrgy at all, I don't think. Olly

No, the theory of the expansion of the universe allows for the universe to be far larger than the light travel distance of 13.8 billion years. If the universe were not expanding then then no two points could be further than 13.8 billion lightyears apart. But it is expanding, so the two points are moving apart during those 13.8 billion years. Conisder an alternative to lightyears. Let's go for pigeon days and say that they fly 500 miles a day. My pigeon reaches you with its onboard watch, which I started when I released it, recording one day. You therefore conclude that I must now be 500 miles away - but you'd be wrong, because I didn't release it from the station platform 500 miles from you. I released it from the train as it passed by the platform and, during the pigeon's flight, I have continued to travel away from you on that train. In that time the train covered 1000 miles so, despite the fact that the pigeon flight time was 24 hours, our separation is acutually 1,500 miles. So in this analogy the movement of the train driving us apart represents the expansion of the universe and pigeon days represent lightyears. The flaw in the analogy (which is otherwise fit for purpose) is itself interesting. The train is moving. In the case of our two cosmological points getting further apart, they are not getting further apart because they are moving, in the normal sense, but because the space between them is growing. For us to move, in the normal sense, we must be accelerated. However, at cosmological distances, two galaxies can move apart without either of them being accelerated simply because each cubic metre of space has grown slightly since the last measurement. If we have enough of these cubic metres (and in cosmology we do!) all these little bits of expansion can add up to a prodigious expansion and cause galaxies to move apart at more than lightspeed. (Remember, they are not moving in the normal sense. They are not being accelerated apart. They can both be at rest while racing apart.) Olly

Whatever Gorann is using is what I'd use! lly

Do you need the filter to fight LP or are you using it to hold down non-nebular light sources in order to find more structure in the nebulae? If you're not using it to fight LP you might consider doing even a shortish run without it it to obtain a natural colour result which you could then use to define colour in the final version, perhaps using the unfiltered data for star colour and reflection nebulosity? Olly

Maybe check out 'Levels and Curves' via Google since these are the key processing tools. It's easier to show these steps in videos, of course. If there was no stretch the bright background just comes from the unbalanced colour channels. Not a big deal. You can see this in Photoshop if you look at the histogram of the image you first posted: First understand the graphs, though. The x axis goes from dark on the left to bright on the right. The vertical axis shows the number distribution of pixels at a particular brightness. Looking at green and blue, and starting at the left, we begin with nothing. There is no graph because the entire histogram is too far to the right. In Levels you need to move the left hand (black point) slider to the right, initially just to the start of the graph. The first little bit of thin black line is the background sky. The main pedestal is the nebula. The thin line after the main pedestal is just the stars. To balance the colours you need to get the top left of each pedestal (shown by red lines) to more or less the same distance from the left. You can only move the pedestals one way - to the left - using the black point slider in Levels. Unfortunately red is already a bit far left so longer exposures might fix that. Don't worry about the sky being too bright. Once balanced it certainly isn't. It's about half the brightness it needs to be at the end. The low red signal probably comes from your filter but it's done well against LP. Then keep on adjusting the black point in levels till your histogram peaks align. A neutral sky, equally bright in each channel, is always my starting point for an image processing job. Olly

Because you'll tell it! 😁 Here's how. 1) Your background, once colour balanced in Pixinsight's DBE, came out at a Photoshop brightness value of 11 to 12, so certainly not too light. I like a background sky of 22 or 23 per channel. This is unstretched. Alternatively, in Curves, if you alt-click Ctrl-click with the cursor on the background it will show you your present background value: 2) Put 4 colour sampler tool markers on different parts of the background, set to sample at 5x5 average (top toolbar) and stretch in levels till your background comes up to 22-23 or so. If you look at the four colour sampler boxes on the upper right of the screen grab you can see the input and output values, so the first marker has gone from Red 11 to Red 20 in this case. G has gone from 12 to 22... and so on. Now you can stretch in Levels beyond this point and just bring in the black point to clip the background back to 22 but, at some point, this will overstretch your background and make it noisy. This is when you go to step 3, though I went there directly from here for the sake of this demo. 3) Open curves, alt-click on the background to make a fixing point on the curve. Put a second fixing point below that to avoid changing the background at all. Now lift the curve above the background in a series of gentle iterations, experimenting with the shape of the curve you make. Essentially you want to stretch harder just above the background than you do higher up, where you risk stretching the stars too much. I think your initially posted image included a screen stretch or 'visualization' even though you hadn't asked for one. You managed to get a remarkably gradient-free background sky! Olly

..................... Then, sound by sight, Will mammoth and sabre-tooth celebrate reunion While a fist of cold Squeezes the fire at the core of the world, Squeezes the fire at the core of the heart, And now it is about to start. I'm never going out at night ever again! lly

Thanks, Ram. I prefer the PI only version because I find the colour more subtle and the posterization totally absent. I wonder how much SII you found and where it was distributed? What I sometimes do to avoid a monochromatic look to the red is add OIII with the brightest parts of the OIII very highly stretched so that the red has a slight colour change in its brightest parts. However, I don't think the Bat has any significant OIII which is why I wonder if a bit of colour variety might be brought in by a similar stretch of the SII. One other idea: what if you used the PI image as a luminance layer over the one posted here? It might let you keep your intense colour while curing the posterization. Olly