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Scooot

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About Scooot

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    Billericay, Essex
  1. Nice one. Was it hand held?
  2. I wanted to try and get a bit more resolution so I took this with my 16” Dob on the Equatorial Platform. A stack of about 100 at ISO100 1/350 over the 18th/19th March 19. The moon is 93% lit, the bright right hand side contrasting with the creeping shade on the left.
  3. Hi Adam, I’m no expert but the big bright star top left doesn’t look very good to me, particularly if I zoom in. I’d hope it would look more round at F4 or F5.6, although I’m not sure what to expect from this lens. Hope you get some more feedback from others.
  4. Fantastic image Adam! Worth every visible Gold Star
  5. Theres an old thread here. I bought the Princeton Tec Remix which I think is great.
  6. On my OO VX10 I seem to recall I tweaked the collimation screws on my focuser to centre the secondary under it. As long as the flat still appears round, & if not it can be rotated slightly, good collimation is achievable. I can still see all the mirror clips so don’t lose any light. Saved adjusting the spider vanes.
  7. Out of interest I put a single image and the stack in subframe selector. SNR is so good so ISO100 or 400 is probably academic and not noticeable. I always think the colours are better at the lower ISO but as the dynamic range is similar that’s probably just my imagination.
  8. This is the one I was thinking of, it was actually a stack of 50ish , 1/20th second, at F10, focal length 600mm. Can’t remember where the histogram was but I suspect it was very near the left edge. I’m going to use my 10” dob on it’s eq platform next time, f5ish 1380 focal length.
  9. Usually around 1/30 second is the right exposure at ISO 100 depending on its phase. ( at about F5) I have a stack of about 20 I’ll have a look at it in PixInsight to see if I can tell how much of the ADC it used.
  10. Here https://web.archive.org/web/20180830114507/http://sensorgen.info/CanonEOS-450D.html
  11. I understand the gist of the noise & stacking issues although I haven’t studied all the above calculations. Back on my Canon 450D, at ISO 100 saturation/FWC is 26614e with read noise of 19.4. As it’s 14 bit my ADC is limited to 16384 levels. so to record the lower signals we need to round up 1.63 adu /e on my camera instead of 5 on yours. As read noise at that ISO is quite high, am I right in assuming this probably won’t be an issue, ie easily reached with random noise. If so ISO 100 could be useful if light levels allow, say on the moon, and I’d benefit from the better SNR at this ISO setting. Or have I totally misunderstood
  12. Thanks again Vlaiv, I’ll have another read later to see if I can follow and understand it.
  13. Thanks for the detailed explanation, nice of you to take so much trouble. I probably used the wrong phrase when I said “sensorless ISO” I meant ISO-less as explained n this site. http://dslr-astrophotography.com/iso-values-canon-cameras/ on my canon ISO 400 or thereabouts seems to be the right spot. They also have a differing view regarding unity gain you might be interested in. http://dslr-astrophotography.com/worry-unity-gain/ I take your point about bit size and the maximum SNR, so remain undecided for the time being of using ISO 100 sometimes or not.
  14. I think you’ve helped me with something else. I was also wondering if there was any advantage to using ISO 100 instead of the sensorless ISO of 400, given there’s very little difference in dynamic range. Using your formula: Maximum SNR at ISO 100 is 162 26614 / sqrt (26614 + 19.4^2) Maximum SNR at ISO 400 is 90.88 8305 / sqrt (8305 + 6.8^2) So on the face of it, when light levels allow ISO 100 is worth using for the potential higher SNR even though the dynamic range is also the same. Have I got this right?
  15. Basically a camera with a greater dynamic range is better in that regard. Stacking increases the dynamic range but it’s obviously better if you start from a higher figure in the first place. I was curious at first because I’d always thought the dynamic range was higher with a lower ISO & with my camera it isn’t between ISO100 and ISO 400. (Or not by much) One thing led to another as I was reading about it and I ended up getting curious about the maths.
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