ollypenrice

That's what I'd do. I don't feel removing artifacts is unethical when all you're affecting is background sky. Olly

Oof, that really is a good image. Tiny Ha regions, nicely done, but really not fundamentally different from LRGB. Olly

If this isn't great amateur imaging I'm going to take up tiddlywinks instead. I no longer watch this woman's videos. They prevent me from sleeping at night. And, yes, she does it on purpose! lly

With your own gear, maybe, but probably not with online telescopes? Olly

This is a very odd galaxy, having only one spiral arm and a wide, smooth central bulge. I'm not too surprised to find that it lacks the 'clumping' needed to trigger star formation, though I think, like you, that there are such scattered regions showing already in the image. If the Density Wave theory is correct I wonder how such waves would propagate in a galaxy with a single, almost circular spiral arm. Olly

I'm not averse to using the tool but, in a case where I disagree with its findings, I'll give precedence to my subjective opinion. I'm certainly a pragmatist and remember Dennis Isaacs saying, 'It isn't the histogram you hang on the wall.' A more general point: we know that stars are 'exceptional cases' in the world of optics. I wonder to what extent we can rely, therefore, on stellar FWHM as an indicator of the resolution of non-stellar details? Olly

When I look at a picture, that's what I do. I look at a picture. When I want to compare two pictures I compare them, and if they are from the same data I can 'blink compare' them. I don't trawl back through loads of numbers agonizing over loads of numbers. What am I missing? Olly

No, the editing is the fun that people buy into when they buy telescope and camera time. Ready made images are already out there. Mine are here: https://ollypenrice.smugmug.com/Other If you'd like any of these, you're welcome. Just PM me. Olly

Folks, believe me. You are truly innocent beginners in this problem. If any of you gets beyond 10% of my problem I'll PM you! lly

I think a good gradient removal tool would flatten your M81 if you just stacked it without flats. Olly

Ah yes, the illumination is changed enormously when the focus is moved. That would account for why your second flat is so flat. Note that you are not focusing on the flat panel, you are replicating the illumination of the original focal position. (The changes in focus between filters are not enough to need new flats, by the way.) Olly

Flats are simply photos of the incoming beam as it hits the chip, which means they all have more or less the same form with only the dust bunnies varying. Neither of your posted flats take this form. The first one is closest because at least it has a bright centre getting darker towards the edges. However, it doesn't look credible. The bright inner circle dims with unusual suddenness and then there is very little further drop-off into the corners. There is also a bright band running upper left corner to lower right corner. The latter cannot be genuine. The second flat is flat - too flat to be credible. Not even my TEC 140-with-flattener is as flat as that and it is corrected for medium format film. What we then notice is that the illumination of the second galaxy image closely resembles the illumination of the first flat, with the same bright inner circle dimming quickly to a very even outer region. My conclusion would be that the second image has been largely unaffected by the second flat, which is to be expected since the second flat is so flat as not to change much when applied. This suggests that the first flat was on the right lines regarding the general illumination but had irregularities of its own in the form of the bright diagonal. This bright diagonal has influenced the second image. What might be worth a try would be this: Set up the rig as it was for the first flats but, during capture sequence, rotate the screen continuously. It doesn't matter if its moving when the exposure is made because you're not trying to image the screen itself. When stacked, this ought to average out any screen irregularity. Alternatively, just try a different light source. I'm pretty sure you present one isn't even. Olly

Measuring you background sky 'per channel' in Ps gives this result: Your blue values are almost double the other channels. This is a check I always perform regularly throughout the processing. Olly

Super. Strange that these have been missed but very nice to see them here. Olly

Lovely. This may well be my favourite galaxy, the one-armed spiral. It may look a bit blue-heavy on my monitor but, hey-ho, it's lovely. Olly

You might consider it!!!

My advice is watch your black point. I suspect that you may have pulled it in too far, giving a very dark sky and cropping out the fainter extensions of your galaxies. There is always a big temptation to get rid of gradients by clipping them out with the black point. That is not the way, nor will it ever be. Don't be frightened of a lighter background sky. Olly

Bravo Carole. This is a murderously difficult target from my place at Lat.44. You've really stuck at it and got something worth having. Very impressive. Olly

The only talk I've ever known! Olly

Really? I think they should burn themselves at the stake in that case. They'll be introducing Layers, next, so you can see what you are doing while you do it.

A decidedly mischievous puzzle maker has been at work here. A childhood friend's granny would have done it easily, though. She used to cut the pieces to fit... Olly

It is totally different. The modifications made to the image by BlurXterminator are made from analyses of that image alone. In that sense they are like lots of other processes. Existing sharpening routines, for instance, identify and intensify small scale local contrasts which are already in the image. Even the most basic interventions, like stretching in Curves, emphasize what is already there. I think the misconception arises from the fact that Russ Croman trained his AI system on Hubble data. This does not mean that his AI somehow remembers Hubble data and later applies them. The reason for choosing Hubble images was, I think, their high quality and consistency. This made a more accurate tool, it did not transfer Hubble information to its memory. (Anyway, with a Samyang 135 I can probably shoot a larger area of sky in one sub than Hubble took in its entire operational life .) Olly

But here you're talking about the true colour of the red coming from the source and I accept your argument. However, there is also the matter of signal strength. Nobody adds Ha to perfect the colour. They add it to lift faint signal above the background and to find stronger contrasts in nebulae, by tracing the hydrogen specifically. This is an artificial but informative modification of the natural signal. Essentially it's a visual convention, I'd have thought. Olly

I'd have thought the accurate way to capture Ha was through a red filter. In this case it is captured in its natural proportion, no? If we add Ha we do so to add information in the form of faint signal and structural contrast. How are you definging 'accurate' here? Olly