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ollypenrice

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ollypenrice last won the day on October 24

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About ollypenrice

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    les.granges@hotmail.co.uk
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    Imaging, Cycling, Thinking, Literature, French culture, Mountains...
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    South east France, Lat 44.19N.
  1. This comes up regularly. To clarify, the formula stating that exposure time increases as the square of the F ratio is predicated on having a fixed focal length and a variable aperture, meaning that aperture is the 'active ingredient.' On top of that we have to consider pixel size because what really determines exposure time is the ratio of objective area to pixel area. And on top of that (oh no!) we have to consider 'regions of interest.' At short focal lengths we may end up capturing an enormous amount of sky in which we are not interested and concentrating plenty of light from our target onto too few pixels. Professional telescopes are often of slow F ratio but work very quickly because they have large aperture and large pixels. Olly
  2. You can't safely compare F ratios at different focal lengths. Oly
  3. These are dusty targets which always need very substantial integration in order to come out looking smooth. In fact they never really do because I suspect the dust is naturally grainy. The Iris shows that the second image has had a harder stretch which goes with its higher noise. I think you just need much longer integration on this kind of target. Olly
  4. Typing paper works fine as a dimmer and can be adjusted easily by adding or removing sheets. With a CCD you don't need dedicated flat darks, you can calibrate your flats by using a master bias instead, though the flats exposure shouldn't be too long if you do that. Olly
  5. Sounds right but if you have a filter of x mm thickness in the train then add 1/3 x to the extension. Olly
  6. Purple? Seriously? It's slightly magenta but I didn't 'go for it,' I found it in the data when the sky was calibrated to parity and the bright stars compared with their spectral classes. Obviously you can trawl the net and find any colour scheme you like but that is hardly a constructive way to inquire into what agrees with the astrophysics. We don't ascertain the date of the battle of Hastings by voting on it. The Hubble team are pretty serious but, unfortunately, they concentrated on the core. This is a warm colour with the spirals striking me as a mid blue. Since they can out resolve everyone else their blue stars will be held more towards to points than amateurs can manage so the blue will be less diffused into the arms. The Hubble image is done in broadband colour and many amateurs will add Ha which, obviously, will slew the blues towards longer wavelengths in exchange for picking out interesting structures. When this is declared it seems perfectly legit to me. Olly
  7. I think that, when the poster is functionally semi-illiterate, we are free to draw our own conclusions. That's one of the few parallels between many very unpleasant social media forums and SGL. Olly
  8. Tom has now posted a 'zoomable' version of our Orion on his website. This is the best way to see it. Put the image to full screen first. https://www.astrophotography.ie/mosaics.htm Olly
  9. Rather than use a pinhole star test why not use the classic ballbearing method? Glue a ballbearing (EG from a bicycle wheelbearing) onto a black card and prop up a torch to shine on it. Observe this from as far away as possible but it will work at 10M. Only light from the bit of the BB closest to the objective will be reflected back towards it so you get an excellent artificial star. Olly
  10. Have you checked that the filter will work OK at this F ratio? Just a thought... Olly
  11. In rather doom-laden era it really is great to see FLO thriving and employing new staff. Well done. Behind your update lies a phenomenal amount of professional retailing skill and creative thinking. Round of applause! Olly
  12. Head-banging pursuit of that outer shell! (I wouldn't really chase as hard as that but this was just for the hell of it.) I couldn't find much star colour but it isn't very intense in my long exposure version either. Olly
  13. I've used tappng for revealing star colour. I don't think I've tried it for going deep. I'll give it a go. Olly
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