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Adam J

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About Adam J

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    Lincoln, UK
  1. On a huge stretch I can see those in my image too, I decided it was not going to happen though as I am guessing I would need 20min exposures as a minimum and my sky is too blight for that.
  2. Looks great, you may want to pull down your green channel a little though.
  3. Interesting, I found the same only for 800. What method are you using to evaluate the noise or is it from eyeballing the final image?
  4. Nice..is this visible already?
  5. I would have to be missing something big. I would be interested to see what he has to say on the subject though mind you. Another way to look at it is a badly focused star...its dimmer right....well that is because the photon flux per pixel is less because you have spread it over more pixels than if (in the ideal case) it was all falling on ~ 25 pixels or so when focused. Now if you have huge massive pixels, one covering the entire unfocused star....the unfocused star will still be exactly as 'bright' or having the same signal to noise ratio as if it was focused...it would make no difference...but when we image that is not a circumstance that happens very often? The scope is always (always) collecting exactly the same number of photons from a target through its aperture. How many pixels of a fixed size you are spreading that over depends on the focal length and hence F-ratio. Same noise in a pixel, same ratio of signal to sky glow irrespective of aperture, but with a reducer more photons hitting a single pixel. You are correct to question it i think. Easy to prove if someone has two scopes of the same aperture and a flat field panel at quite some die distance from the scope.
  6. I am not convinced that is entirely incorrect to be honest as you are deciding the photon flux between less pixels the s/n will improve at the expense of resolution at the same exposure length. The problem with that is when your object is only subtending one or two pixels prior to reduction as in that case you don't gain anything....so dim stars will remain the same leading you to believe that the limiting magnitude is unchanged....however if you had something like a wide field nebula that is uniform on small to medium scales then as you reduce the focal length it will increase the pixel photon flux and hence improve s/n...but that's not strictly the same as making something brighter...but it will improve the image in some cases as in your m51 example exactly the same number of photons are being collected by the scope but are being focused onto fewer pixels. Forget about the overall wider fov those photons were always being collected by the scope it's just without the reducer they were falling off the edge of the sensor. So I still say there is no myth!
  7. Wow DSLR's and F10 optics dont normally get along so this is a real achievement! I am surprised by you using 1600ISO though as opposed to 800ISO but I suppose that with such a slow scope the balance will shift in respect to the optimal setting and 1600 may win out when 800 is the best option at say F5.
  8. I am about to build something very similar to your mini obsy design (1.6x1.6x2.0m clam shell roof), I was wondering if, with use, there is anything you would change about your design? Apart for the conduit that is
  9. Silly question but is USB over Ethernet literally converting the USB into TCP/IP protocol and back or is it just sending USB serial data down an RJ45 cable (in which case it would be more accurate to call it USB over cat5/6)? If so can you then send it over a network power adapter?
  10. My problem with running armored cable is that it seems impossible to get it in short lengths and its so so so expensive. I need about 4 meters to get to my obsy and you cant buy less than 20 meters of the stuff locally.
  11. As wimvb says its probably got more to do with the 15um pixels, very high QE, cryogenic cooling and a read noise along the same lines as a ASI1600. That is enabling outstanding performance even at F10. By my reckoning that is 11 x more collecting area per pixel than say a Atik460EX with 60% less read noise and thanks to the extreme cooling probably next to no thermal noise in a 1.5min exposure (all that is without factoring in that the image was clearly 2x2 binned). Am going to take a guess at it having a per pixel S/N ratio of something along the lines of 20 to 30 times that of the 460EX if placed on the same scope....of course the 460EX would be massively over sampled and only capture 1/30th of the image shown above. So in terms of signal to noise I would guesstimate that is equivalent to about 2.5 hours of data from a Atik 460EX (150hours for it to make the equivalent mosaic). In my opinion there never really was an F-ratio 'myth' its more a f-ratio misconception. Talking about F-ratio in terms of signal to noise per pixel, is fine and correct, just so long as you and your audience understand the limitations of the argument, the argument being that s/n ratio will stay the same for a given F number irrespective of focal length. You just need to accept that you will lose resolution and understand that the argument breaks down as the angle subtended but the object being imaged approaches the angle subtended by a single pixel. All the stuff floating about concerning less information being gathered is a valid but totally separate argument. If we are really saying that some people actually think that their little amateur scope is equivalent to a 2 meter scope because they share the same f-ratio? If so then I am not sure what that is but I would not call it a 'myth' more a fundamental misunderstanding of the measure. If you are not saying that then I am not sure I understand what you are trying to convey? I dont know maybe what I am not actually understanding is the nature of the myth itself??? I just think that the short exposure performance at F10 in this case is everything to do with the camera and that the resolution of the image is to do with the size of the primary mirror. But however you put it the slow f-ratio is not helping and a larger primary with the same focal length for a faster f-ratio would give a superior result in an even shorter exposure. What you are doing above is comparing two totally different measures both of which have a place but mean totally different things. The F-ratio of a optical system is a useful piece of information to have as it tells you the light gathering power you have for a given focal length at a quick glance nothing more nothing less. Edit: I SHOULD PROBABLY SAY NICE IMAGE !
  12. Why buy new? Get a second hand one in good condition and you are away. You can also pick up astro modified cameras on the second hand market.
  13. Ok, what is the exact model of your mount and scope? Also do you have a finder scope?
  14. Looking good with the H-a you should try OIII also as it works very well with a cooled cmos sensor even a color one keep blue and green. Ill be interested in the QHY247 when it comes out.
  15. For imaging I would get the 130PDS without hesitation it has a large following for a reason.