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About ollypenrice

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  • Birthday 12/02/1953

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    Imaging, Cycling, Thinking, Literature, French culture, Mountains...
  • Location
    South east France, Lat 44.19N.
  1. Another M51

    Heheh, well maybe I felt the same when Rob Gendler gave our latest M51 an 'excellent' on Facebook yesterday! This is a supportive community - which is great. Olly
  2. Camera orientation

    The alignment of the camera has no effect on the orientation of the diff spikes on the sky. You could (but you wouldn't!) rotate the camera between each sub and the diff spikes would retain the same orientation on the sky because they are created by the spider vanes. To rotate the diff spikes you would need to rotate the spider vanes - ie the telescope in its rings. The camera angle has nothing to do with this. I'm not sure what you mean by aligning your coma corrector. It's round...? Because a quick slew to ensure that you are aligned along RA and Dec using the method I mentioned earlier is so easy I really do think it's worth doing so that you don't lose field of view in adding later data. Olly
  3. Camera orientation

    No, it has no effect at all on guiding precision. It just makes it ten times easier and quicker to add new data at some later time. Olly
  4. Another M51

    You have a very good result. I would have two immediate priorities for taking the image further. Firstly I think it is a bit colour cold, so a bit on the blue side. I think the reds might need a slight lift. Then the background sky is rather 'busy.' A large dither - 12 pixels or so - between subs will greatly reduce colour mottle in DSLR images. Using normal noise reduction which uses pixel-to-pixel communication will probably introduce the 'oily' look which is unattractive. Dither is the best way with DSLRs. Rob Gendler's image is a benchmark but note the exposure time and the apertures used - and bear in mind that his processing expertise is at the top end of world class. Olly
  5. M51 single nighter, TEC140.

    What can be achieved by avoiding exasperating reflectors and replacing them with reliable small pixel cameras and refractors is a very topical subject! Best of luck. I think you're on the right track. Olly
  6. Nothing to do with SCTs. The F ratio myth is a long story but it is not always true that a fast F ratio speeds up capture. Having been a big advocate of this on SGL I'm reluctant to get involved again but Alacant has linked to a thread, I see. Just Google 'the F ratio myth' and you'll get a good grasp of why F ratio may, or may not, speed up capture. For practical proof check out the very short exposures processed on here by SGL members using data from the slow F ratio Liverpool Telescope. It's a no brainer. Big telescopes get more light and this light cannot and does not just disappear. Olly
  7. M51 single nighter, TEC140.

    Honestly, I don't think so. I think your problem lies elsewhere. If the guide corrections are in the right direction and of about the right magnitiude they may overshoot but they will never drive the mount in the wrong direction on a second input. You might expect a see-saw guide trace of over-corrections but not a swipe on the elbow sending your pen across the page, so to speak. All that ever happens to my Mesus is that in times of high turbulence (and we do get them) the RMS values rise but the underlying behaviour remains as usual. I suspect you have a SiTech problem. You won't be the first! I run the old ArgoNavis/Stellarcat versions of the mount and never have any bother. Have you considered Lucas Mesu's adaptation of the Losmandy polarscope? It's very good. Being observatory based I don't use mine but one of our guests says it takes him less than a minute to polar align his mobile Mesu using this system. It's 100% software free and so can be expected to work! Olly
  8. Astro-Tech RC 14"

    It's a great shame that Astro Tech can't be bothered to help you. Frankly that's disgraceful. I can't help with the collimation but your experiences define exactly why I stay away from this kind of scope and stick to simple designs. Is there an optical shop within reach of your home? It would be great if you could employ them not just to sort it out but to take you through the procedure. Olly
  9. Camera telephoto vs refractor

    For good results I go for the HEQ5, autoguided. Another issue with lenses is that stars are very exacting targets. It is hard for optics to get them right at fast lens F ratios but if you stop them down with a diaphragm you'll get multi bladed diffractions spikes. You can make a front aperture mask and leave a lens wide open, though. Olly
  10. Camera orientation

    Square to RA and Dec for me. To get it there, take a sub of about 5 secs while slowly slewing. This will create trails. The angle of the trail is the angle of the camera to RA or Dec. Rotate till the trails align with the chip in either landscape or portrait format. My kit is never taken apart so I only do this to go from landscape to portrait on occasion. Olly
  11. M51 single nighter, TEC140.

    This one, a TEC 140 triplet Apo on Mesu 200 mount. Olly
  12. M51 single nighter, TEC140.

    Dear boy, your wish is my command! A small circle of inner core was indeed burned out. After constructing the main image we went back to the RGB-only data and did a soft stretch in which the core was still OK, then subjected it to rather brutal unsharp masking to wrench out some contrasts. This wasn't pretty but we only wanted the tiny inner core, which we then applied as luminance over the tiny burned out original core, discarding the rest. Photoshop layers a go-go. It might have been better to shoot a few short L subs but I often rescue saturated bits of luminance by creating a luminance from the shorter RGB subs I usually shoot. Olly
  13. M51 single nighter, TEC140.

    Thanks, S. I really do have a lot of M51 data but I can't say that I have found hard evidence of much more than you see here. That doesn't mean it doesn't exist but if I pushed my data beyond this point I'd be painting. Others may have better data, of course. Olly
  14. M51 single nighter, TEC140.

    It's cropped, Chris. On the net I wanted to show the galaxy at close to 100%. In TIFF format it holds up quite well at full size but a second equivalent night's data would be needed to take it all the way there. Diminishing returns, of course. Olly
  15. M51 single nighter, TEC140.

    Thanks all. I should have said '8x10 mins colour per channel' but I'm sure you worked that out! Olly