ollypenrice

I agree with Adam, you need to know your guide values in arcseconds. However, the spikes across the stars do look like diffraction. Could this be from something in a part of the lightpath that didn't go to Es Reid? Olly

But sometimes not enough that work! 😁lly

You'll need new cables at some point, anyway. Personally I have a stock of the things for this reason. If you swap a suspect cable and it proves to be innocent you can just put the new one back into stock for when one of the old ones does fail - as it will. Remember that this failure will happen on a Friday night with three clear nights on the forecast... Olly

I'm surprised nobody's mentioned this, but there is something rather odd going on in this image. I'm afraid I can't offer an explanation for it, though. It's very obvious in the first version but still present, to a much lesser extent, in your excellent rework. (The rework really is excellent.) The thing is that the colour simply drops dead below the line in this screen grab of the original. My own data do show hints of a similar effect but something in your workflow may have exaggerated it. Was there a radical change in the processing between first and second? If so it would be a good idea to identify it because it's going to be important. Another thing: a key aspect of image processing is managing different parts of the image in different ways. Sometimes this is called The Zone System. In M42 it involves processing, and even capturing, the Trapezium differently from the rest. If you don't have a set of short exposures for the Trapezium it isn't the end of the world. You can do a separate stretch for the Trap, much gentler, and you can boost the saturation to get colour back into it. Then you can combine the two in an HDR process (High Dynamic Range.) There are countless ways to do this. You can do it manually in a layers-masks program like Photoshop, or use an automated version of the same (again in Ps or similar), or there are HDR packages like Photomatrix to try. I dare say the other astro-specific programs have something as well but I don't know them myself. This target absolutely does need different stretches for Trap and the rest. Your data are worth the effort. Olly

Combined here are data sets from a RASA8/ASI2600 OSC and Tak 106/Atik 11000 mono (Ha LRGB.) RASA data in partnership with Paul Kummer, Tak data in partnership with Tom O'Donoghue. This region lies close to the soul nebula and comprises two VdB nebulae and the diffuse Sharpless Ha nebula. I already had a large Tak mosaic covering this target and extending to include the Soul so, when Paul Kummer added a RASA8 capture, I decided to do a hybrid image using both. The RASA made much lighter work of the VdB objects but, without a filter, was left struggling on the Ha. I saw this morning that Gorann recently did a great job on this target a few weeks ago. Olly

I can't help you with calibration like this. I just keep it simple and use AstroArt. Calibrating a dark with a bias does not involve subtracting the bias from the dark, as I understand it. The bias is used to scale the dark, usually because the darks and lights have not been shot at the same temperature. Given the complexities of CMOS bias I've no idea whether this works for CMOS calibration or not. I think you'll need Vlad for chapter and verse on this. 😁 Olly

😁 No, you don't have to keep sucking! You evacuate the air till you have the figure you want then close the valve. Ralf does not, so far as I know, have any commercial intentions for this instrument, nor does he intend to use the 'sucked tube' as a permanent arrangement! This was a sneak preview, if you like. I mentioned it in this thread just to show how easily a mirror distorts - or easily relative to the wavelength of light, at least. Olly

Please note that I'm not slagging them off. I simply suggested a line of research. If you'd like to hear about my own (and one of my customer's) experiences of after sales then it will have to be via PM. All I have ever said publicly about this firm is that the ODK14 I used for a few years worked very well. I repeat that here. Olly

Why are you subtracting a bias from a dark? The bias signal is contained in the dark. The bias signal is the faintest of the inherent camera noise. Brighter noise is thermal in origin. If, for some reason unknown to me, you subtract the bias from the dark then you'd get the thermal noise minus the faint bias signal - which is what you've got. The question is, Why do you want it? 😁lly

For the bad news, Google Orion Optics UK customer service. For the good news, look through the scope, not at it. Such blemishes will have no effect on the view whatever. If the figure of the mirror is as they say then the views will be excellent. Olly

Triangular stars are the classic indicator of pinched optics, which you've pretty much confirmed. Mirrors distort easily. Ralf Ottow has a reflector in which an airtight chamber lies beneath the mirror. He can change the figure of the mirror by reducing the air pressure in the chamber - by sucking on a tube connected to the chamber! I've seen this done before my own eyes (which were rather wide at the time!) 😁lly

The easiest astronomy question I've ever been asked. Mesu 200. In around ten years it has still to cost me a single lost sub. (I've dropped a few due to middle-of-the-night brain fade but the mount never has.) That's not a 'good' record, it's a 'perfect' record. Maintenance during these years? None. Olly

I think this may be what's happening, yes. Olly

Column defects are quite common and if you stacked in AstroArt you could lose them by using the column defect feature. I dare say other stacking software has an equivalent but, if they don't, they should! The bias won't show you a column not responding properly to light, remember. I thought you had a dark column, or rather two, in the master light. Olly

I don't know why stacking hasn't removed this but it's a totally trivial defect which can be cosmetically repaired easily. I deal with worse than that, believe me! For diagnostic purposes it's worth noting that there are two pairs of parallel lines, a light and a dark both repeated. If you look at a single sub, what do you see? Is it two parallel pairs like the master or is it just one pair? Or something else? When you stacked, did you use a sigma stacking routine? That's the best for this purpose but not all Sigma routines are equal. AstroArt's, which I use, has improved over updates of the program. AstroArt also lets you identify bad columns prior to the stacking stage and the columns will be given the average values of the pixels on either side. And it also has a 'Remove Line' feature which you can use when all else fails. Olly

Fascinating. Thanks for the link. Olly

Does it flicker when dimmed? Some do, giving inconsistent exposures. Olly

Small scope + small pixels = great result. Olly

I'd clean that, certainly, because pollens and other active agents can degrade coatings. I'd point it slightly downwards, spray it with distilled water and isopropyl alcohol plus detergent (recipes are on the net) then dab it with cotton wool (one dab per bit of cotton wool) to get the bulk off. After that I'd spray it again, wipe it with cotton wool, again one wipe per ball, using curved strokes. The key principles are to avoid wetting the inside of the tube and to avoid scraping the corrector with gritty stuff picked up by the cotton wool. I guess Baader fluid would do instead of the water-alcohol-detergent brew. Olly

Look through it. You can also look at it but it's important to remember that looking at optics is not how we use them. In the last quarter of a century I've looked through, or imaged with, a tiny handful of optics which looked perfect. But I've used dozens which performed perfectly. One of the best SCTs I ever looked through had an as-yet uncoated corrector plate because the builder hadn't yet got to that stage... Olly

I wouldn't attempt any mixing of twin-scope data without Registar. It's fairly expensive, it's a one trick pony, but it's a darned good trick! I've done a lot of dual rig imaging with twin Tak FSQ and twin TEC140 and there's a lot to be said for it. However, the finer your pixel scale is, the harder it is to avoid trailing from flexure on one scope. This would probably be less of an issue with a small refractor and you could get away with a less costly alignment device. I have always used the Cassady T-Gad which is no longer in production and was brutally expensive even second hand. FLO have possible candidates. Unless one side has a much larger FOV than the other, you'll need some kind of alignment device. Interesting reading tomato's solution to the dither problem. My solution was not to dither and rely on the different noise profiles of the two sides. With the low noise of modern cameras I don't know how import dither is, in any case. I don't miss it. At best, when both rigs are the same, your maximum benefit from a dual rig is, by definition, one F stop. Something like the RASA blows that out of the water. However, I've used two dual rigs and one RASA and the twin Tak dual rig was easier, though a lot slower, than the RASA. The twin TEC at high res has always been difficult. Finally, we have to be careful in comparing small-scope RGB data with large-scope binned RGB even when the pixel scale is comparable. The signal, however, will be far weaker in the unbinned small-scope data. I suspect that adding at least some RGB from the main scope would probably be necessary. I can't be sure because it's always been a principle on our dual rigs to use the same scopes and comparable cameras on both sides. Olly

This is not my field and I'll gladly stand corrected but in my present understanding... ...wind does not cause lift by getting under the lower surface. Some recent research has changed the textbook explanation https://www.cam.ac.uk/research/news/how-wings-really-work#:~:text=“A wing lifts when the,along the lower%2C flat surface. but it's commonplace for roofs to be 'torn off' closed buildings which have a zero windspeed on their underside. The stationary air's pressure on the underside is capable of blowing off the roof when the wind causes the pressure to drop on the upper side. This is counter-intuitive because we naturally suppose that the lifting energy is somehow contained in the highly energetic wind when it is really coming from the air pressure of the stationary air below. Olly

How about re-fitting the roof it it starts to get windy? I can imagine that being easier with two people. Olly

With my LX200 I found the GPS was far more trouble than it was worth and that I could set up the alignment far more quickly without it. Olly

Please, I don't hold you responsible! It's the good folks at DSS who should know better and it was to them that I was referring. Olly