ollypenrice

One time SGLer Annie Morris posted this Starlink allsky footage on social media: https://www.facebook.com/antimorris/videos/556769332318522 Olly

I'm willing to believe software said you were within 10 arcsecs but much less willing to believe the software is right! It is incredibly difficult to get as close as that in reality. I think there are lots of possible sources of rotation if you are dismantling the gear between sessions. Wim's suggestion is foolproof: use star trails to orientate the camera along RA and you are sure to have the same orientation. Olly

If you are seeing movement in real time, then what you saw moving must have been relatively close - meaning not in deep space at stellar distances. Barnard's star has the fastest known proper motion relative to the Earth but its motion cannot be seen other than by comparing images taken over time.) You saw one point of light move into visual alignment with another. (It would be better not to call them stars because that's an assumption and certainly incorrect in at least one of their cases, since stellar motion cannot be seen in real time.) However, one of the points might have been a star, the other something much closer and in motion. This would mean the sudden appearance of the burst of moving points of light at the moment of alignment would have been a chance event. Unlikely but not impossible. What happened to the relative motion between the two points of light once the 'fireworks' started? If one point did not carry on moving past the other then we can probably eliminate a line of sight effect and conclude that both points were at the same distance (close to Earth) and collided, releasing fragments which caught the light... Along with millions of others, I once witnessed a rocket fuel dump in perfect observing conditions at our observatory and in the company of Dr René Dumont, probably one of the last professional visual astronomers. We saw a roughly ten-moon-sized nebula (the main hydrogen purge), a horizon-to-zenith halo caused by refraction, a moon sized nebula (a final purge) and a point of light (the tumbling rocket) moving slowly westwards and downwards. It took about ten minutes for them to go from the south where we first saw them to the western horizon. This gives an idea of how fast sub-orbital objects appear to move. I don't know at what altitude the purge took place but it was clearly sub-orbital, yet movement appeared very slow. If you were seeing faster relative movement then the points of light you saw were considerably lower-closer, despite appearances to the contrary. One thing's for sure: if a point of light appears to be moving in real time, it is not a star. Olly

The flat you post is suspicious in just one respect: there is no vignetting in the lower left corner. It's not impossible that this represents the truth about the way your optics are illuminating the chip but I have never seen optics vignette clearly on three corners and not at all on a fourth. Apart from that, the flat looks perfectly credible. Personally I expose for slightly less time to bring the histo peak down to about a third of full brightness but this isn't all that critical. So my question would be, why no vignetting in the lower left hand corner? Does that corner come out too dark in the final image when you apply this flat? Olly

You've said this before but I'm left a bit baffled. The log stretch in any program is what it says it is, a log stretch which has a mathematically pure relationship with the linear data. It's not 'out of date,' it's a basic building block which you can take or leave. It's what you get if you stretch in Levels, but you don't have to stretch in levels, you can stretch in Curves and, in so doing, have full control over shape of the Curve/nature of the stretch. You can also stretch under masks made by an assortment of means, you can import ready-made stretches like DDP if you like, you can blend different stretches in layers and so on. The Layers log stretch is one tool out of many. Re Pixinsight, it certainly isn't compulsory. I still use it almost exclusively for gradient removal (DBE and ABE) and green noise reduction (SCNR Green.) These processes usually give me good colour calibration as a welcome by-product. Other than that, it just doesn't work with my way of going about processing. I'm visual-touchy-feely, if you like, so the highly metaphorical user interface in Ps suits me. (Layers, eraser, Dodge and Burn etc etc are really just Photoshop metaphors for the underlying maths but they work for me in ways that PI doesn't.) PS owes its commercial success largely to the intuitive nature of these metaphors which draw on the old techniques in graphics, printing and film photography. It's purely personal, I think. Olly

The stars!

Especially if you disable the unused guide direction and guide in Dec only in the one direction imposed by the polar misalignment. This technique has worked for me with a difficult mount prone to Dec backlash. You have to reverse the direction after the flip and find which direction it is by trial end error, but both are easy to do. It is, in effect, the Dec equivalent of running east-side heavy in RA. Round stars: these are often used as the arbiter of good guiding but they shouldn't be. They tell you one of two things, either that your guiding is good or that it is equally bad on both axes. In the latter case, which can happen, you'll suffer a loss of resolution and signal to noise ratio. Round stars are not all they're cracked up to be. Olly

@vlaiv 😁lly

I can fix non-round stars in Ps easily enough but slightly oval outer haloes are not so obvious. I'm just fooling around with this problem at the moment. I didn't really notice them much either, I must admit. That man from the East has a lot to answer for! Olly

You're too deep, Vlaiv! 🤣 Re-doing the circular cable guide is on my list but I've been fixing lots of other things as well. The robotic rigs all run without attention for ages then they all need something doing at once. I'll get to it in the end. Meanwhile, don't look at it for too long without turning it upside down for the sake of your neck! Olly

I wondered what the RASA/CMOS would be like on star colour and have been pleasantly surprised. I thought the combination of super-fast F ratio and reduced well depth (after my Atik 11000) might give little star colour but in fact there's a lot. This may be connected with one of the scope's weaker points: stars tend to have a soft outer glow but, being soft and faint, this glow will contain a lot of star colour which can then be pulled in towards the cores in processing. I did this partly by the simple use of Noel's Actions Increase Star Colour and partly by selecting the stellar cores and blurring them to bring in the outer colour. Olly

It's early days in setting up this mount and, so far, it's proving a little inconsistent, taking a while to settle down to lower RMS values. The first few runs included one or two wild tracking jumps every hour or so, though in the last run all 60 subs were good. The dynamic balance still isn't perfect because of the offset focuser but I need to do a bit of bracket making to fix that and haven't yet found the time. Paul also suspects that there may be some unusued software inputs in the system which might interfere with it. (I don't understand this bit so can't be clearer.) RMS has been around 0.4" at best to around 1" at worst, so certainly variable. Edit: Yes, I think LBN 617 is around the central star and, as you say, the rest looks like IFN. Normally you lose me with the maths: now you're being too cryptic!!! Fishing? Can of worms? Nope, you'll have to give me a clue! 😄 Olly

Lynd's Bright Nebula 617... Humph, so where's the bright bit, Beverly??? For me, Google only finds one other image of this object, near Polaris, but it's been fun trying to extract what bit there is. 129 x 3 minutes using RASA 8/ ASI2600 OSC/ Avalon Linear based in one of our robotic sheds Observatoire Per Frejvall. Software (the hard part!) and capture, Paul Kummer. Hardware and processing, me. Pixinsight for ABE and Photoshop for the rest. I was surprised that AstroArt agreed to sigma-stack 129 50 meg images but it did, in only about 15 minutes. Then it turned out that we had another run of about 40 subs which I failed to spot on the capture PC, but that will be for another time... Paul has been heroic on the software side. Olly

I just think it's white clipped. I think you've stretched the bright signal a little too far, leaving it rather flat and colourless. A gentler stretch will fix it easily, no doubt. Olly

Very nice indeed with those dusty shapes setting of the rich starfield. I'm learning my way with a fast scope as well and thinking about how to control the bright end - ie the stars. Olly

A feisty image with something to say. It does prioritize the brighter nebulosity, though it looks to me as if some of the fainter signal which tempts you is already there in the data. (Your black point is set quite low, which may just have clipped a bit of it. Maybe, maybe not...) If you look at the handle of the Witch's Broom you can see a second 'handle' diverging from it in Ha. This is a good way to gauge the depth of a Veil image. One way to bring out more of what you have is to use Curves. Pin the background where it is and then stretch just above it. Here's an example. The lowest dot on the curve is a fixing point. The next up is bang on the background. The lift comes above that. I have to say, I'd be tempted to go the extra mile with such a good image. Olly

Beautiful processing. The fact that it was a complex processing procedure is totally invisible in the image, which looks blissfully natural and effortless. The nebula is delightfully lit and the powdery little stars let it speak out. This really is an admirable piece of work. Bravo. Olly

Attractive result. I suspect it would take a little judicious sharpening in key places. Olly

Nice! I'd watch your back point though: it does look a tad clipped to me, costing you the outer regions of the galaxies... Olly

I prefer 5! Well, I prefer the RGB 'Trichromy' process in 5, which became vastly more complicated in 6. I still have 5 on one machine and do Trichromy on that because I can't be bothered to learn the new version in 6. (If there was anything at all wrong with the version in 5, I might be interested in learning the later process but there isn't. It worked perfectly for me just as it was and I'm irritated by the change.) On the other hand I've just returned to OSC imaging and the debayering in 6 is far better than I remember it. Guiding: I used to guide in AA but switched to PHD. To be quite honest I'd just go for PHD2 for guiding. It's outstandingly good, and very easy. It also has a vast user base for feedback on peculiar problems. The AA star feature remains fast, easy calibration. This morning I offered it 129 subs, each of 50 meg (!) and asked it to debayer then sigma-stack them. Quite honestly, I was expecting this to fall over but no, it took ten to fifteen minutes. Olly

If this is for deep sky, NOT the Cat and NOT the wedge, whatever you do! Both are bad news for deep sky imaging. HEQ5, autoguided and either small refractor or small Newt. Olly

I'm not sure that bias are useful with CMOS cameras... They certainly are with CCD, however. Olly

Colour gradients probably won't be corrected by flats. I find, certainly with OSC cameras, that they seem to derive from the chip. I recently processed some OSC data from a pre-flip session and a post-flip session. The images from each session had a red-green imbalance which changed sides at the flip. Your second image is certainly better. Very good indeed. Its top left corner is flat and it has less noise in the dark section around the bottom, half way along. In Ps you might try going Image-Adjustments-Selective Colour-Reds and dropping the cyans in red by moving the top slider left. This is a demon trick for getting Ha signal to shine. Olly

That's worth bringing up, certainly. However, I'm in the south of France with outside temperatures occasionally reaching 40C with mid-thirties commonplace. Both the TEC 140s based here live permanently in the observatories where temperatures go far higher than that in the daytime and winter temperatures go down to the minus teens routinely. (There is no possibility of dismantling the rigs since they are part of an dual imaging installation which takes days to fettle.) We haven't had a problem. Olly

TEC. In imaging terms those stars are not big at all, they are very small. Similarly, in imaging terms that is as close to a halo-free Alnitak as you are ever likely to see. It is phenomenally well controlled. You're looking at a deliberately under-processed image, one to which only the simplest of log stretches has been applied, since my aim is to show the native optical performance of the TEC. To see why I think it's remarkable you'd need to look at other broadband images of the Flame Nebula. (Narrowband filters hold down stars in ways that broadband filters don't, but broadband give natural colour.) I don't want to link to other people's images and say, 'Look, your Alnitak is a big white blob,' but I think you'll find plenty of big white blobs out there if you look! Olly