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ollypenrice

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ollypenrice last won the day on June 16

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About ollypenrice

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    les.granges@hotmail.co.uk
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    http://www.sunstarfrance.com
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    Imaging, Cycling, Thinking, Literature, French culture, Mountains...
  • Location
    South east France, Lat 44.19N.
  1. I wouldn't buy these instruments for deep sky imaging. Even on an equatorial wedge they are a poor idea for many reasons. I second the advice to read Making Every Photon Count, available from FLO, the site sponsors. The mount is the most important part of a deep sky imaging setup. Olly
  2. ollypenrice

    sh2-119 in Ha

    The object and framing are sensational. There is something slightly 'scratchy' about the look which, I guess, just needs more data to rectify. The Veil is bright - and easy, visually, even in small apertures. I doubt that this object is at all comparable but what a treat to see it. Olly
  3. ollypenrice

    Vulpecula widefield.

    Here Paul and I added two panels to the left hand side of our recently posted SH2-86/88/90 image. This has, as intended, brought M27 into the field. The Dumbell isn't normally seen against a particularly dusty background so we wanted to confirm that the dust and gas really does thin out to the east of the red Sharpless objects - and so it does. This isn't often imaged in widefield yet it's rather a splendid patch of Milky Way, we thought. On average, an hour per colour and three hours' Ha for each of the four panels, shot with the house twin Tak/Atik 11000/Mesu 200 setup. Olly
  4. ollypenrice

    First Light FSQ 106 and .6x reducer (F3)

    If you're not happy with that you're a hard man to please, Rodd!!! Olly
  5. ollypenrice

    What Constitutes Good Guiding?

    I think it's the seeing. It's exactly the same for us even with pretty dark horizons. Olly
  6. ollypenrice

    What Constitutes Good Guiding?

    Vlaiv is perfectly correct that the round stars test is almost meaningless but at least with round stars you can produce an attractive image. When setting up the first Mesu we always had round stars but by tuning the guide parameters they got smaller and smaller! I don't think there's any reason to believe that the HEQ5 is less accurate than the 6 provided both are within payload. Any backlash adds to the guide error and the worse the seeing the more it does so. (When corrections are few there is a reduced tendency for the mount to be sent oscillating across the backlash.) So losing the backlash is a very good idea. The other ways to combat backlash are to run slightly east heavy and slightly polar misaligned. East heavy keeps the drive in 'push' mode and the misalignment means you can disable guiding on one direction in Dec, letting the other 'push in the direction of correction.' This does work and won't stop you from doing 15 minute subs. The duration of guide subs is also something to tune in the light of prevailing conditions. Our EQ sixes thrive on short guide subs if the seeing is good because they have pretty rapid PE. However, if the seeing is bad this has them chasing it, so we do better with longer subs which average out the position of the guide star's image. (It's worth remembering that the guide trace has no way of knowing where the real star is. It only knows where its image is. So very short subs do give a better trace but is that a trace of the real star or just its image? Curses!! ) The other variable within the guide trace is the position of the scope between corrections. Again we have no means of knowing, but Avalon claim that with their backlash-free belt drive the correction is fed in faster so that, between guide inputs, the true location of the scope is on target for more of the time. With any backlash oscillation in play it's a good bet the situation between inputs will be worse. Olly
  7. Regarding the Hyperstar, take everything Starizona say about it with a large pinch of salt. I regard some of their claims as flirting with the advertizing standards laws. There will never be anything 'easy' about imaging with an F2 system whose light cone is so steep as to make the focal depth only a matter of microns. This is a problem when the rather primitive moving mirror focus of the SCT is all you've got and it also means that the slightest tilt will see you in focus on one side and out on the other. In the smaller sizes it is important to have a camera which doesn't intrude into the light path and in all cases you have the problem of how to route the cables in order not to create odd diffraction effects around stars. As regards cutting down on exposure time, it does and it doesn't. Take M51 without the Hyperstar and you'll get a screen-filling galaxy. With the Hyperstar you'll get a wide starfield with a tiny galaxy in the middle. It is hardly fair to say that this will reduce imaging time because the images have little in common. On the other hand it is a very fast system for widefield. I'm not saying don't do it, I'm just saying don't be persuaded that it is going to be easy. And once you have sorted out the system with Hyperstar in place, are you going to swap it back and forth with the long FL system? I very much doubt it... Olly
  8. ollypenrice

    Filters on OSC cameras

    As Star101 ably demonstrates, you can usefully use NB filters with modern CMOS cameras. There is a significant loss of resolution compared with mono and the same filters but the small pixels mean that you can still get a very decent result. If your aim is to add NB data to natural colour, which is how I use it, then it would be well worth doing. For all that, I do personally feel that mono is more productive per unit time. Olly
  9. There are a few 'beginner mistakes' to avoid. The first is regarding payload as being the definitive factor with mounts. It is't, necessarily. In deep sky imaging it is far more helpful to think in terms of accuracy of tracking under guiding. How accurate does your tracking under autoguiding need to be? A rule of thumb would be to say that your guide trace RMS in arcseconds needs to be no more than half of your imaging pixel scale in arcseconds. If it is more than about half it will impact on your real resolution of detail. (Beginner error 1b is to believe that round stars prove adequate guiding. They don't, they just mean that your guiding might be equally inadeqate in both axes.) This http://www.12dstring.me.uk/fovcalc.php is a handy website for finding the pixel scale of a given rig. Now, what kind of accuracy can your mount deliver? You need to try it to find out. I find that my premium mounts (Mesu) consistently deliver about 0.3 arcsecs under guiding while my EQ sixes are variable but can generally deliver about half that precision, which is still not bad. (Note the abundant use of the term 'about' in this reply because that is the name of our game.) The other beginner mistake is to take a naive view of F ratio. In the camera world the focal length doesn't vary when the F stop is changed so it's the aperture which varies. In this case the 'F ratio rule' makes perfect sense. When both aperture and focal length vary the rule goes straight up a gum tree and leads to confusion, brawls and long nights in detention... lly
  10. ollypenrice

    3 Sharpless nebulae in Vulpecula.

    Thanks Vim, that's great. All is revealed. Olly
  11. ollypenrice

    M51 - 30 hours

    ...and the message is: nobody ever had too much data! That's great, and the extra data, despite laws of diminishing returns, open up lots of new possibilities which you've exploited very well indeed. Most exciting. Olly
  12. ollypenrice

    3 Sharpless nebulae in Vulpecula.

    The top panel was 6x10 minutes per colour and 7x20 mins Ha. The bottom panel was similar but also had a small amount of luminance. I don't remember just how much but not much at all. In making the 2 panel I didn't start from scratch but stretched and processed the new top panel by eye till it was a reasonable match with the already-processed bottom one. I then just asked Registar to calibrate it and combine them, which it did almost seamlessly. One small region of visible join needed fixing simply by pasting the original panel over the one which the line showed and using it as a patch, feathered in. Olly PS Ha was added to red in Blend Mode Lighten and also used at very low opacity indeed as Luminance.
  13. ollypenrice

    3 Sharpless nebulae in Vulpecula.

    Great, many thanks. LDN792 I'm sure it is, as you say. My internet is struggling with the other links up here in thunderland (!) but I'll follow them up. Olly
  14. ollypenrice

    How good is this?

    I wouldn't be comfortable in linking to someone else's image as a demo of 'how not to do it' and the PI community have really toned down the over-use of HDR wavelets in the mast few years. I realize that the wavelets are derived from the data but they used to impose a uniformity which belied this, in my view. Olly
  15. ollypenrice

    How good is this?

    Oh it is! Just think of it as an extended south Pacific beach... Olly
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