ollypenrice

A celebratory fly-by! Red Arrows and Patrouille de France... Olly

I've seen colour twice but never green. The best was a bolide which fragmented in a flash of red and blue. The other was just red. The red and blue one was seen by several of us and we agreed on the colour. I was alone for the red one. Olly

I was looking down at my feet to avoid falling over on my way down from our robotic sheds at 21:50 French time, 20:50 BST, when a diffuse flash of light in my peripheral vision made me look up and I caught a white fireball. It was heading from Zenith to south but the fact that it produced enough light to make me look up from the ground is quite exceptional. It peaked at about 30 degrees above the horizon, which makes me wonder if the original flash which made me look up might have been from a different but related meteor, perhaps even brighter. We hadn't even reached astronomical darkness when this happened. Olly

Very true! I never fail to point this out, giving it the full pedant, to anyone else watching. It's a curious convention. It would be interesting to see the reaction if a film director decided to do it properly. Another oddity was the convention by which old style landlines in films always had cables long enough to allow the actors to roam their homes while chatting away. Nobody ever had such transatlantic length phone cables, ever. Olly

I live in fear of forgetting to use data as a plural! I always have to remind myself that that's what it is. As a 'sort-of' scientist and an English teacher (de-frocked) I'd cop it from all sides if I got it wrong. 🤣lly

Why the shorter subs for L? I always shoot for longer in L and then remove it where it has too much signal, notably in stellar cores. Olly

I think that's exceptionally good. Globulars really are hard and I've yet to see a single rendition which was perfect in all respects, but this is a beauty. The stars are powdery small and precise, which is obviously very important. The general glow of the core also shows the propellor beautifully. I think what we have here is actually a good call: the brighter stars are very clearly defined against the less bright. The medium bright-to-faint are not so well separated but, if we're going to sacrifice something in a stretch, that's a good thing to sacrifice. Yes, I think that's great. Olly

The cross below roughly marks the centre of the frame, so that's more or less where the telescope is pointing (there being the possibility of slight misalignment of the optical axis within the OTA, droop in the focuser etc.) The centre of rotation, however, is very close to the marked star. Now, what does that tell us? Ah, now I'm not very good at these spatial awareness conundrums. Thinking aloud, the mount thinks it has pointed the OTA to what lies at the centre of the frame but actually it has offset it slightly to the small star at the centre of rotation. A difference between the direction of the saddle plate and the direction of the telescope (ie cone error) seems like a good fit. However, if the marked star were the guide star and there were polar misalignment, wouldn't we also see rotation around that point? I think we would. How can we distinguish between the two? By knowing where the guide star was. If you were using an OAG or had aligned your guide scope fairly well with your main scope (which serves no real purpose) then the star at the centre of rotation might be the guide star. I think it more likely that it's not, making cone error more likely. Another way to check would be to look for field rotation between the first and last sub on the same side of the meridian. If it's the polar alignment solution you should see some rotation around the star in question even without a flip. None of this comes with a guarantee! Olly

A quick glance at a third party website showed a list of 15 currently available Canon brand EF-s lenses so I'd call that more than a very few. However, I was really thinking about the OP's interest in using telescope optics as well, at some point. Telescopes capable of covering 35mm are much more the exceptioon than the rule. And then there are the ones, like the Takahashi Baby Q, which purport to do so but don't. Olly

Be sure to check that any optics you buy can cover full frame chips. Those which can are still in a small minority. For most AP users the larger pixels will be an advantage because it is very easy to over-sample. Olly

Beautifully done, Steve, and an original choice. Clean as a whistle. Olly

The problem, for me, with threads like that is that the theorists - who understand the situation better than I do - do not agree with each other. My solution is to experiment and find out what works to my satisfaction. Sometimes my findings are at odds with what the theorists tell me I should find. Since it isn't the theory I'll be hanging on the wall, I go with my findings. That doesn't mean I'm contemptuous of theory. That would be foolish in a scientific discipline. It just means that, in the absence of sufficient competence on my own part, I go with what works. Olly

Is this complex gradient present in a single sub exposure straight from the camera? Olly

OK. I don't know how the background extraction works in Siril but, in Pixinsight, I find it far better to apply a minimum number of sampling points than to cover the background with them. The idea is to extract the large-scale gradients. I don't know if this would be relevant in this case. Olly

The link just takes me back to the top of this thread... Olly

Several aspects of this process strike me as odd. 1) With a CMOS camera a master bias is not necessarily suitable as a dark for flats. With CCD a bias does work fine. I would try making dedicated flat darks. (Same settings as the flats themselves.) Note: I would not, on a Newt, attempt to make any kind of bias or dark on the scope. Light leakage is hard to prevent. 2) I make a master bias or master flat dark and then apply that, at the stacking stage, to the flats - which means each flat is calibrated before it is stacked. I don't know how important this is but it works for me. 3) Why multiplicative stacking of flats? I, and everyone else I know, uses either average or median stacking for flats. The authors of AstroArt, in which I do my stacking, recommend average so that's what I've always done. I'm highly suspicious that this may be your problem. Olly

What do you mean by, 'Doing background extraction?' This term usually refers to a post-processing technique rather than to the application of flats as part of calibration when stacking. Could you take us through each step of your calibration and stacking workflow? Olly

Professionally, I have had two encounters with OO UK. I have absolutely no intention whatever of adding a third. Olly

I've just popped next door to my workshop and measured my Geoptik panel. It's 380mm and I bought it late last year. (Actually it isn't really mine, it belongs to one of my robotic clients but I lent its predecessor to guests and fried it by giving them the wrong power supply in the dark! How to spend a lot of money very quickly without getting any fun out of it...) It's a good product, nothing like those useless and short-lived Aurora panels with their naff snap-off wiring. Olly

As Vlaiv says, the only flat that's any good is one that works. If you think you can decide this from theory, then may the force be with you. I've had flats which worked, flats which didn't, flats taken with a method that worked and then stopped working, with no change that anybody could identiffy... When you stretch data as we do, you render it incredibly sensitive to initial conditions. You may think you are doing exactly what you did last time but you may not be. On the plus side, flats which work are (in my experience) very durable. I've used the same luminance flat on all filters for up to 9 months because it worked. I couldn't care less whether or not it ought to have worked. It did so I used it. Olly

Let's think about this. If we post a linear image we get a black background and a few stars. Not very interesting. If we extract the image's information in a way adapted to what our eyes can see, we see an object in much of its complexity. Now you can't possibly object to this. The stretching process is a process of exaggeration and lies at the heart of astrophotography. We exaggerate the faint signal by a greater amount than we exaggerate the bright and that is the primary skill of the astrophotographer (in my view.) In a similar way we exaggerate the colour information we have captured. Sure, some imagers impose pre-determined notions of colour on their images but I don't see a difference in kind between your processing and the original. Have any stars turned from blue to red or vice-versa? I'd have thought not. Olly

I'd love to look at the data but I've no chance of downloading that file other than via something like Dropbox. We communicate largely by pigeon here in rural France... 🤣 I'll have a look at the stretch though. Olly

There's a lot to like but the core is saturated or, at least, sufficiently stretched to have lost stellar resolution. Is the core like this in the linear data? I'd suspect it probably isn't so I think a more differentiated stretch would preserve more stellar separation in the core. Personally, I'm not a fan of any ready-made stretches that I've tried but I don't know the one you used. Olly

Would suit painter and decorator with OCD and plentiful supply of sandpaper and paint. Yikes, look at those gables! Very nice, though. There's a similar house up in Canada. Similar but - cooler. And on that note... Olly

These targets are absolute murder: at the eyepiece they glitter, in images they rarely do. This is a good rendition, for sure. If I were processing this I'd try one last thing, a bit of sharpening, more pronounced in the core and dropping off to nothing by the edge of the cluster. I wouldn't normally sharpen stars but, in this case, it would be a matter more of adding contrast to the core than of sharpening it. Sharpening is simply a small scale boosting of contrast, after all. Is this your full FOV? I think globulars benefit from a bit of dark sky context to make them pop. Olly