ollypenrice

I agree with Martin on all counts. I might just ease down the green a tiny bit since it's quite high in the upper left of the image in the dusty region. Olly

I don't use it, Freddie, I use PI, but I had a play with the AA version to see what it did. Olly

Some kind of gradient removal tool is more or less essential. Astro Pixel Processor has a good one, as does AstroArt. Pixinsight's are also excellent and possibly the best. Even from dark sites colour gradients are a persistent problem. I've been using Astronomy Tools (formerly know as Noel's Actions) for years. Very useful. Olly

Our late friend Per Frejvall lived in Stockholm and was involved with the old telescope there. Thanks for posting. Olly

Sure. This is Photoshop. We'll assume the Ha is co-registered to be an exact fit on the RGB image. 1) Select and copy the Ha (CtrlA CtrlC). 2) Make the RGB active and split the channels. Minimize green and blue for a tidy screen. 3) Paste the Ha onto the red channel (CtrlV.) 4) In the Layers dialogue box change the blend mode from Normal to Lighten. (Now the Ha top layer will only be added to the lower red layer where the Ha is lighter.) If the Ha isn't doing much you can stretch it further right here in situ over the red. I tend to use Curves for any extra stretch so I can pin the background Ha value where it is. We don't want to lighten the background sky because that will end up reddening it. 5) Flatten (CtrlE) the Ha onto the red. 6) Merge channels. Choose RGB mode and put the now modified R in red, the G in green and the B in blue, of course. 7) If the HaRGB looks overdone in Ha you can paste it onto the original RGB and vary the opacity to have as much or as little Ha as you like. Ask again if any of that's unclear. Olly

I've never managed it naked eye even from here. In the next life I'd like good eyesight! Olly

Oops, sorry Wim! (Senior moment...) 🤣lly

This is my method. It isn't a 'quick and easy' one but we do specialize in large mosaics here and are aiming for the best we can get. Stack all panels in L and RGB and keep them separate. Edge crop them all and run them through DBE in Pixinsight. Partial stretch in Photoshop (maybe half way to full stretch.) Set the background sky to the same level in all panels. Is this a very large mosaic or just a 6 panel or less? What follows is done to the L panels and the RGB panels separately for combining later. Very large mosaics need a template to get their geometry consistent. A widefield camera lens image of the target area, resized upwards to the size of the projected image, can be used. It may look terrible but it's only used to determine the geometry and does not appear in the final image. APP will also make a very good template. Smaller mosaics can be left to Registar (more of which in a minute, but start with a central panel as your reference image.) In Registar, ether register all panels to the template or to a central panel. Calibrate the panels (one click) and save the registered calibrated panels for patching any artifacts which appear later. Combine panels in Registar. (In very large mosaics it isn't practical to do this in one go so make blocks of 4 or 6 panels to be combined later.) Take the combined image(s) into Ps and inspect them for artifacts, notably for lines at joints. (The Equalize function in Image Adjustments will highlight any latent joint lines brilliantly.) If you have a visible joint take the registered calibrated single panel which covers it and apply it over the joint in Ps Layers, feathering it out where it isn't needed using the eraser. Once the full image is clean give it its final stretch and processing. Combine L and RGB. A lot of work? Yes! 🤣 Tom O'Donoghue worked for about six months on constructing our 36 panel Orion https://www.astrophotography.ie/ and I spent about 40 hours processing the 32 panel recently shot by Yves Van den Broek. https://www.astrobin.com/g82xf7/B/?nc=user Don't panic, 6 panel mosaics are much easier. Olly

Second hand gear goes for around 60% of new, generally, if in good condition. Rarer items may be worth more. There isn't much that can be invisible to inspection and still wrong with a telescope. Sometimes refractors can be out of collimation and tricky to fix but an SCT is a tolerant design. If it looks OK it is very likely to be OK. Mount electronics are another matter but that's true of anything electronic. Olly

If smaller filters don't vignette then the advantage of larger filters is precisely zero. My widefield rig (old school fluorite Tak FSQ106N with full frame CCD) has a roughly 23% dropoff in the corners due to vignetting with 2 inch mounted filters. With flats this is a non-problem despite using the rig primarily for mosaics where good field flattening of individual panels is essential. Personally I'm perfectly happy with Baader LRGB but the advantage of Astrodon (and doubtless Chroma) for Ha and OIII is enormous. The obvious way to test vignetting is to take a flat and measure the illumination in the linear image across the frame. Unless the dropoff is considerable in the corners you don't need larger filters. What will they change? Olly

I agree with that analysis, as I've said elsewhere. Olly

For me, movement is the key to spotting it. If you're dead centered on it you may look straight through, so to speak, and not see it. If you nod the scope past it and back, though, it may pop. It has an extremely even surface brightness (though 'brightness' is hardly the right term!) I agree with Martin that bins may be the best bet. Olly

The image I posted mostly isn't mine, I just processed it. I had 12 hours of OIII to add to Yves' 90 minutes of OSC. The image in Wim's link is clearly better. To be fair, a Squid as good as that in 21.5 hours is pretty good going. It's a terribly faint object which is why it escaped detection until a few years ago. Olly

That is impressive. Perhaps I'm being unduly doubtful about NB with modern OSC. In a target with reflection nebulosity as well I think you'd want to shoot some unfiltered data for the blues but that's a potent image. Olly

That's a great start. In Photoshop the Eyedropper menu has a Colour Sampler Tool. Set this at the top to 3x3 radius or 5x5 and you can put four sample points on the background sky around your image. It must be background without nebulosity. The info palette will then show the readings in red, green and blue for your background. I aim for 23/23/23 for a neutral background and this also gives an idea of the image's overall colour balance. Olly

Usually we post JPEGs directly on the forum and links to full resolution files if we're asking for a more detailed analysis. Some members don't like downloading files from unknown sources and some (like me!) have slow internet connections. Olly

Almost everything will show to some extent in an OSC camera. The exceptions are the very faint narrowband nebulae. For instance the Squid (Outters4) was entirely invisible in the OSC data which made up Yves Van den Broek's capture of a great swathe of sky in Cepheus. This is a close crop of the Flying Bat from that enormous image. The green Squid Nebula didn't show at all so I added it from my own OIII-mono capture. Also, lower left, you'll see a small blue reflection nebula. While this did show in the OSC data it was very faint and not very blue. Again I enhanced it in processing from my LRGB image from the same region. I get the impression that the present CMOS OSC cameras are very sensitive in the reds, hence their excellent performance on Ha regions, but are less sensitive in blue. (Yves' OSC data went deeper into the Ha than my Ha/mono CCD, which came as a surprise.) If the OSC cameras are tailing off in sensitivity towards the blue (just my impression and not set in stone) then they may not be too hot at finding the OIII which lies on the green-blue border and tends to be faint. It's important to remember that filters don't add light, they only block it. A NB filter only works because it allows us to go deeper in a selective wavelength by exposing for longer and stretching harder. You won't get more NB signal with the filter than without it. In fact you'll get fractionally less. But you'll be able to islolate it for selective processing. The obvious broadband targets would be galaxies, clusters and dusty objects. Some people add Ha to galaxies find the star forming regions and emphasize them but this isn't compulsory. (I used to find my OSC CCD rather disappointing on galaxies because it just seemed slow but I think OSC has been transformed by CMOS cameras.) However, I'm sure your camera will sing on the wintery Ha targets as well - Horse, Rosette, Cone etc etc. Olly

Of course the entire conversation is predicated on the tensed theory of time being correct. This is the theory of time in which there is a past, a moving present and a future. The theory is not without its flaws since people separated by cosmological distances cannot agree on when it is 'now.' The simultaneity problem. But the worst thing about the theory is that we tend not to think of it as a theory at all. That's all it is, though. Spooky! Olly

Yes, I was thinking of vertebrates. Olly

What really happens in evolution is, I think, that species and environment evolve together. There are a few species in which there are no males and so no genetic mixing. This has the advantage of making perfect copies but it has the disadvantage that there are no mutants who might be better adapted to a change in the environment. (The female is stimulated by the male of a similar species but his genes are not incorporated into those of the offspring.) If their environment changes these species will be doomed. In an environment in which running or flying faster confers survival advantage it will evolve. But, equally, an opposite evolution may appear in different environments. Flight in birds comes at a high price: they must be incredibly light and have a high power to weight ratio with small fuel tanks. That's why, in suitable environments, many bird species discard it because the price is too high. They can do better without it. If we took your hierarchical view we would have to regard the ostrich as a degenerate species and the seagull as a higher one. This would surely be unsound. To do this would simply be to invent, in our own image, evolutionary virtues and vices and apply them out of context. The notion of an evolutionary hierarchy partially accounts for the extreme hostility with which Darwin's ideas were met. They carried with them the implication that the 'lower orders' of humanity might evolve to equal the 'higher.' They were seen as enabling 'upward mobility' to the consternation of those who judged themselves to be at the top. In truth the hierarchy is spurious. Olly Edit: I've ignored female preference in all this. Why does the peacock wear a fancy tail? Because his wife told him to. And then there's this: 😄 https://www.facebook.com/photo?fbid=10217245377757853&set=a.1235683743581

...not so sure about this. In some interpretations there is a move towards 'improvement' but in others there is just adaptation. Is there a hierarchy of value in evolution? It's very likely that the last species to go extinct will be those which are the least evolved, such as microbes in rocks. Humans invent notions like 'higher' species because they have created a hierarchy which places them at the top. But imagine coming to Earth as a alien and comparing insect society with human society. In which would you see the greatest harmony, the most productive co-operation? Which would you see as the more likely to avoid destroying itself? I'm inclined to see top predators and increasing entropy as remarkably similar... Olly

I'm always surprised by those who think that humanity will endure beyond a few seconds into the future, in the scheme of things. Humanity is a transient little thing that popped into existence a few seconds ago and will pop out of existence in a few seconds to come. Enjoy it while you can. I do. Rendering humanity immortal by fantasizing about inter-generational space travel leaves me bemused. Darwin was the first to see the truth. Extinction is a part of nature. The fact that you fear it is not going to make it go away. What is so terrible about non-existence? Did anybody worry about it before existence came into being? 😁 Olly

Understatement of the year? 😄 I hear what you're saying but I recently processed a multi-gigabite mosaic from a CMOS OSC which, without specific Ha filtration, had dug deeper into the Ha signal in a region I've imaged with my Atik 11000, and the CMOS data was deeper in 90 mins OSC than mine was in many hours of mono/Ha. The CMOS data was shot with a focal reducer, mine not, both in Tak FQ106 scopes. My point is that the enormous CMOS advantage I found in the data I processes is entirely absent from the OP's Cave data. Olly

Is your pickup prism optimally aligned with the chip? It should come into the middle of one of the long sides so it can come deeper into the light cone and so get more light and less coma. Once you've done that you've done all you can and the others above say it works fine anyway. Olly

Having just had a play with this data I don't think it's all right, I think it ought to be significantly better. The noise floor is very high. I've imaged this target twice with my old school Atik 11000 (50% QE) at two apertures, 140mm and 106mm, and my S/N is considerably better than this. The noise also has an odd look to it. It's a slightly elongated 'grain' to my eye. My first suspicion is that calibration may not be working as it should. I would go through everything you can, particularly darks. Right settings, right temp, etc. Then I'd check the stacking parameters again. Olly