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ollypenrice last won the day on December 31 2019

ollypenrice had the most liked content!

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About ollypenrice

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    Imaging, Cycling, Thinking, Literature, French culture, Mountains...
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    South east France, Lat 44.19N.
  1. While theory favours a mono for guiding, without doubt, I used both mono and OSC versions of the Atik 16ic for many years as guide cameras and found no difference. None whatever. Maybe if guiding with little light, as in an OAG, you'd feel the difference but I was using the same ST80s, FLO's finest, that I use today. Olly
  2. How do you define what's acceptable? Simply turning camera pixel count into print DPI ignores the resolution in arcseconds per pixel at which the image was captured. Ultimately the quality of the image depends on its resolution in arcseconds per pixel, its eventual signal to noise ratio and the skill of the processor in terms of noise reduction, sharpening and many other things. I don't think you can just say, 'This chip can be printed out at that resolution.' This may or may not be possible with daytime images (I don't know, I don't take them other than casually) but astrophotos are different. They have been highly stretched and heavily processed and they are often seeing-limited in resolution. Olly
  3. I keep stacks. So that might be 'red, 12x15 mins' and 'Ha 10x30 mins' etc. I then keep the processing steps till space requires me to delete them. I'll generally keep the un-post-processed RGB but, ultimately, I'll end up binning the rest. Olly
  4. What you don't really want is the standard spring-loaded guidescope alignment device. While this is handy for visual finders because it can be easily aligned, the spring-loading of guidescopes ranks alongside the constructing of fireguards in chocolate. Olly
  5. But not easy to focus. How did you do it here? Olly
  6. Tony Hallas says the same thing and his DSLR images are very good indeed. Use a 12 pixel dither. Even with set point cooled CCD I'm not always convinced by darks, just convinced sometimes. Surprisingly it's with my noisy Kodak 11 meg chip, which gives darks like a snowstorm, that I find that the subtraction of a bias and the use of a bad pixel map gives the best results. It's an easy experiment to make, in any event. Olly
  7. Hey, that's really great. The object itself is unreasonably huge and yet, even so, you've casually pulled in another Ha object to the right! Wow. Olly
  8. Nicely resolved at the small aperture of the lens. I like the mascara on the nebula, less so on the bright stars. (I still use your 'bling' expression for Ha in galaxies and can see 'mascara' being just as useful!) This is a very punchy and exciting image. And what an object it is! Olly
  9. If you decide, first, on the resolution in arcseconds per pixel which your sky's seeing and your mount's accuracy under guiding will support then that's a solid start. So... if you use PHD and key in your guider's pixel size and focal length it will, in operation, give you a guide RMS in arcseconds per pixel. For a rule of thumb, multiply this by two to get your maximum useful resolution in arcseconds per pixel. An RMS of 0.6 arcseconds will support an imaging resolution of half that, so 1.2"P/P. These are just numbers but they are not entirely meaningless. They will help you approximate reality. You can get to 1.2"P/P in any number of ways by varying focal length and pixel size (or by binning to change effective pixel size.) Just don't expect a free lunch. If you go for larger aperture you must remember that optical production costs are proportional to that aperture and are also proportional to focal ratio, faster being more expensive for quality 'x.' For what it's worth I've personally called a halt to my search for resolution by using 5.5 inch refractors and small pixel cameras to give me 0.9"P/P but I have exceptionally good mounts. I could probably squeeze a bit more resolution out of something larger but at the cost of a lot of fiddling. In your shoes a scope I would consider is the Skywatcher ED120 Pro. https://www.firstlightoptics.com/pro-series/skywatcher-evostar-120ed-ds-pro-outfit.html I think the 6 inch RC would beat it if you managed to get it just right - but would you? Those who succeed in collimating RCs say it's easy. Those who don't say it's difficult! Olly
  10. Indeed. You can't heat an observatory while observing from it. Olly
  11. Point taken. But if we take the 'billions of stars therefore alien life' argument and add to it the observable fact that the 'laws' of physics and chemistry of the local environment seem entirely consistent with those seen everywhere within observation range, does the argument not gain a dimension? If we found that, not too far from the sun, the local laws did not apply then the 'billions of stars' argument would fail entirely. When we combine the 'billions of stars' with the scientific consistency of the universe should we not then invoke another guiding principle of astronomy, the Copernican principle, which advises us to beware of believing that there is something special about our immediate environment? Neither Occam's Razor nor the Copernican Principle are arguments and they are certainly not proofs, but rather they are notes of caution which it might be wise to sound at the hypothetical stage of theory-building. Or am I missing a philosophical point about the 'billions of stars' argument? That's quite likely! Olly
  12. The whole business of telescope temperature may be not quite as it is usually described. There is no need that I can see for a closed-tube instrument to be at ambient temperature. It's just that when it is at ambient temperature there should be no tube currents. However, tube currents can also be prevented by insulating the tube, as James mentioned, so that its internal temperature is uniform and constant. That's the bit which matters. I often wonder if we might not be able to make a slightly heated and temperature controlled 'jacket' to put round our closed-tube 'scopes to ensure that the main tube is at a uniform and constant temperature slightly above ambient to prevent dewing. For imagers there is also the mechanical aspect of instrument temperature to think about. As the fabric of the scope cools it oontracts, so altering focus. A visual observer just gives it a tweak but an imager using long subs may find it drifting during an exposure. For this reason I run the dew heaters on my fast refractor in summer, not to prevent dew (there isn't any here in summer) but to slow down cool-down and, therefore, focus drift. While a dose of hair drier will clear a lens the effect on image stability it utterly catastrophic and the dew is back before the turbulence has settled! A far better remedy, in the absence of dew bands, is to drape a warm dry towel over the optics and give it five minutes. But dew bands just work. Olly
  13. This sounds like a debayering issue. In order to release the colour the image must be debayered prior to stacking, though most software will debayer then stack from a single command. This is a well-written article. https://altaircameras.com/why_debayer_before_stacking/ Olly
  14. Don't ask too much of an EQ5, unguided and driven on only one axis. That has a fighting chance of delivering decent low resolution images but you are imaging at very high resolution - about 1.26 arcseconds per pixel if I haven't slipped up. That means you really need a tracking precision of about half that - say 0.6 arcsecond. That's quite a big ask for an autoguided EQ6 let alone an unguided EQ5. I know that, when you start out, you think, 'Why do I need dual axis drives if I'm polar aligned?' and the answer is that, unfortunately, at the insane resolution we're asking for, there are so many small errors in our systems that we just do. I agree with Marvin, above. You've done well. Olly
  15. No, the necessary tools of my trade. I need stuff to work for my guests - though it's nice that it works for me, too! lly
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