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Grogfish

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About Grogfish

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    Nebula

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    Hertfordshire
  1. Check out “The No EQ DSO Challenge!” thread - because it’s all Alt-Az the exposures are all sub 1min (or near enough). Worth a look through. I also suspect there’s something of a self-fulfilling prophecy regards image quality. If you’ve got great gear, then you have a high resolution, high bit depth sensor and can track for multiple minutes. Plus with some lovely LP filters. And given you own all that kit, that’s precisely what you do. Hence fantastic images from “long exposure”. And as it works so well, why try anything different. On the other hand most people that are doing “short exposure” are doing it because they can’t afford any better tracking. That also tends to mean you can only afford cheaper sensors with lower bit depth and lower resolution (like my GPCAM IMX224), and lesser (or no) anti-LP. So the “short exposure” pics are taken at say 1280x1024 12bit (that’s me!) compared to perhaps 5000x3500 14bit for “long exposure”, which is another reason why some images look better than others. Gosh, could really sound like I have chip on my shoulder, but I really don’t ?
  2. Firstly I should say that everything I do is very short exposure by most standards (typically 25s or so) because I’m Alt-Az. And given my vary modest setup I’m pretty pleased with the results - stacking 100 frames does considerably reduce noise. (Except that with Alt Az I have frame rotation, and that means the number of frames being stacked drops dramatically near the edge - thus cropping is needed (or shutting up and putting up ?)). Also I’m a firm user of SharpCap Pro, so I greatly appreciate Robin! However, whilst I felt Robin explained noise in some detail, he didn’t really seem to touch on the question of sensitivity... And a short exposure will be less sensitive than a long one, no matter how much you stack. So for some objects (or for the particular appearance you desire), you will simply need a certain amount of exposure. I’m a rank amateur, but my experience has already shown me that, for example, there’s a certain amount of nebulosity I can image in M45 using 26s no matter how big the stack. If I could image with say 45s, I’d expect to see much more nebulosity. The comparison images he used were of M42, but actually I don’t think that was a great object to choose because it’s so bright. If for example he’d picked M33, I’d have eaten my hat if 100x1s would show anything of the galaxy at all, whereas at 4x25s you certainly do see something. Increasing bit-depth of the camera would presumably also be a way to improve the effective sensitivity (via stretching). Ahh, to be able to take subs with triple digit exposures!
  3. Many thanks for pointing this out @Skywatcher130 ! I’ve found Hertfordshire provides Sky at Night through RBdigital, and I’m considering it as £5 off the Council Tax each month ? Definitely a top astro tip for all to check out.
  4. Hi Arran Many very well respected forum members have given you the down-low on your idea, and I believe you can safely rely on their judgement. However, if you want to give it a go, I say, give it a go! Do it because you’ll enjoy the project, and because it’ll be fun to play around with telescope bits, and because you’ll learn a heck of a lot doing it.... but just don’t hold too much prospect of it working. You might want to take a look through the DIY astronomy section to see what others have got up to. Perhaps take some pictures of your project as you go and maybe start your own thread?!
  5. Very nice image, and a fascinating galaxy - not one I recall seeing before. Thank you for sharing
  6. Welcome from another Herts resident! Glad to hear you’re already enjoying the new scope. We’re having some great weather at the moment for it ?
  7. Through thin clouds this evening I've had my second go at the Rosette Nebula, and my first go with bias frames. Using Altair IMX224 with 200mm lens at f4 piggybacked on my Nexstar 4se. I'm super proud of this picture - it only took me an hour or so this evening, and I'm pretty limited with Alt-Az, but slowly improving my technique and I think I'm starting to get some reasonable results - hope you like it too. 60x26s, 24 darks, 100 bias. DSS+GIMP I found the bias frames do seem to have helped out with a bit of a left-right gradient I was getting before. Interestingly when I shot them with the very shortest shutter speed (0.1ms) the noise pattern seemed very high... so I slightly slowed it to (0.3ms) and found the noise dropped right off. When I tried processing with the 0.1ms and 0.3ms bias frames, I found the 0.1 made the stacked image far worse, whereas 0.3 helped. In summary, when running the IMX224 at very high shutter speeds it looks like maybe it (or the Windows driver??) engages some kind special mode which unfortunately also makes it very noisy. Well, that's a lesson learnt! Also wished I tried using bias frames before!
  8. Hiya Jonny I have a few suggestions that may be of help. Firstly NGC7000 is a large object and if you’re using your DSLR with the Nextstar 8 then you’ll only see a tiny chunk of it - even with an amazing mount you’re so “zoomed in” that you’d probably struggle to expose it. Eg in screenshot from SkySafari I’ve got the blue circle what you’d see in a 32mm plossl, and the blue rectangle showing a Canon 450d, both with Nexstar 8. Only the “Gulf of Mexico” would be framed. If I understand your profile right you’re in the UK too, so NGC7000 is really really low in the sky at the moment. So perhaps suggest a target higher in the sky and smaller targets - perhaps M81 or M82 or M1. However, I’d also agree with the suggestion to try piggybacking the DSLR instead. I’ve been doing this almost exclusively with my Nextar 4 for some time. There’s a Celestron adapter for around thirty quid, and just using a camera lens you already own (somewhere 50mm to 150mm to start with maybe) the Alt-Az tracking will be far more able to keep up (the focal length being that much shorter). At least consider it as a way to get practiced even if you want to go back to shooting through the Nextstar later. Either way, yes, using DSS is pretty much a requirement. Good luck!
  9. A bit bodged together in my case, but the garden storage box makes a handy place to rest the laptop.... And if you don’t have to skip around kids toys in the dark then you don’t know what you’re missing out on! (Scope only so low because I’m having a late crack at M33... and for once I seem to be winning?)
  10. Thanks Rotatux. Sounds like I need to be braver at stopping down the 135mm. The Samyang looks fantastic, but out of my price range sadly. Regards star bloat I’ve not satisfied myself how much it’s due to poor focus, aberration, stacking technique, or bloom from a pixel well overflowing on the cmos (is that the right terminology?!). Not really thought about it like this before, but I suppose I need to work out how much each of those is contributing to star bloat to push my imaging on a level... that’s given me some homework for the next month!
  11. What aperture do you tend to use with the 200mm? Do you run full open, or shut it down a bit? I’ve also got a f/2.8 135mm cosinon lens, but I’ve not had a chance to try it out much- and when I have I wasn’t particularly impressed- it appeared very soft at f2.8
  12. Sooo... I have an M42 to C mount adapter - cost around £18 on eBay. I also have the Altair GPCAM bracket that holds the camera and provides various screw mount points. That I attach to the Nexstar 4 using the Nexstar 5/6/7 piggyback camera adapter. And because it’s designed for a SCT, it doesn’t quite fit.. however mounting the piggyback holder reverse does seem to fit ok (and not block the eyepiece holder), but it means the holder (and thus the camera) stick out to the side of the Nexstar, rather than being on top. All a little Heath Robinson... but.. kinda starting to get some results!
  13. Ooops, my mistake! In my own mind I’d always thought of this method as the “raspberry of doom”, but I love the IBC!
  14. Madly and unjustifiably, I always harboured a secret hope that somehow Opportunity would get to Beagle2, flip out the stuck solar panel, and spring it to life! Oh well, another dream crushed ? I suppose I feel slighty sad, and perhaps bad, for these shutdown probes and robots on distant worlds. Still, it’s pretty incredible any of them made it there in one piece in the first place. Am I right that Opportunity was lifted down on the amazing “sky crane”?
  15. Good question! For M31 it was around f/4.5, but I tried stopping it down a little more on NGC2244, around f/5.6. Not sure it made a lot of difference to sharpness. While I nothing about camera lenses it seems pretty sharp, even wide open at f/4. And my thanks to @Bobby1970 who sold it to me a while back! Viewing this page now on my iPhone the colours are all a bit mangled (or absent) compared to on my laptop last night... so... if you’re looking at my pictures and wondering what’s going on then close your eyes and imagine Hubble took it ?
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