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bobro

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About bobro

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    Star Forming

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    Isle of Wight

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  1. A curious thing about AP - the more you do the more you see in an image that can be improved. That's the way it (art?) is, but take pleasure when others appreciate an image. For sure practice makes for improvement - looking back at a previous image you were happy with makes this evident.
  2. Impressive image for 2 second exposures! And with M110 captured too.
  3. For comparison, here is an image of 10 sec taken with my a 50mm fl lens. Trailing is just starting. So 2 sec doesn't seem too far off for 200mm fl static lens.
  4. It might seem strange, but the ISO makes no difference to the image captured by the sensor - what really makes a difference is the exposure time. For unguided imaging with a 200mm fl lens, try 15 second exposures to start with. The idea is to maximise the exposure length without star trailing, therefore capturing as much detail as possible on the sensor. The ISO determines the amplification used when reading the image from the sensor and is less important, with a value of 800ISO being a good starting point. When an image is processed it can be 'amplified' in a similar way to the ISO setting on the camera. Andromeda is not an easy target due to a bright core and faint detail further from the centre.
  5. m22

    There can't be that many stars, can there? (PS - I think you may have missed one....)
  6. The EQ3 DSO Challenge

    In an effort to have goto I've been playing with a CG5 (sacrilege I hear you say!) using AstroEQ and found the same sawtooth using single direction guiding a couple of nights ago. You can see from the graph the mount wants to go in the same direction as guiding, which is wrong as the mount should be pushing against guiding and the slack taken up before guiding starts. In any case I wouldn't use single direction guiding as dithering is such a useful feature (used with my EQ2) and requires bi-directional guiding. So I've done my best to remove the slack in DEC waiting for a retest. What I would rather do is put the stepper motors on the EQ2 as its guiding performance isn't much different to the CG5 and much more pleasant to carry around (I'm learning more about guiding and can make the EQ2 guide better as it wasn't being controlled enough). Putting a motor on RA is straightforward but DEC only has a limited range of movement. Can anyone offer a suggestion of how to modify the EQ2 DEC to allow 360 degree control with a stepper motor?
  7. Cardboard Coma Corrector

    I wanted the f ratio to be 6 as there shouldn't be much coma at this f ratio, so just divided the folcal length of 650mm by 6. The f ratio is the focal length divided by aperture.
  8. 650mm fl /130mm aperture reflector scopes are great for imaging with the fast focal ratio of 5, but they do suffer from coma aberration due to this. My scope is no exception and seems to have especially bad coma. As coma should reduce with increasing focal ratio, as an experiment I cut a 108mm circlular hole in a piece of card and placed it centrally across the front of the OTA, effectively changing the focal ratio to 6 with the reduction of the aperture from 130 to 108mm. Below are two single subs : one without the card(f5 at 120secs) and one with the card (f6 at 180secs). I was surprised by the great reduction in coma in the f6 image. (Almost full Moon so rather bright subs.) Of course the reduction in aperture means an approximate 50% increase in exposure time, but it could be useful for brighter targets.
  9. Andromeda Galaxy (M31)

    Lovely capture though the framing obviously lets it down. Why not try a mosaic? Would make for a super image.
  10. The EQ3 DSO Challenge

    Although the 6 min version has a slightly different resolution, I find it to have the smoothest colour transitions . Not a lot in it though! How many subs in this version Nige? Bob
  11. The EQ3 DSO Challenge

    Thanks Wim, though you could be corrrect in that checking the tightness of the worm gears would be worthwhile in case binding is taking place. Much quicker than a stripdown!
  12. The EQ3 DSO Challenge

    Hi Wim, As the setup in question isn't guiding but just tracking in RA (hence DEC not driven and RA always driven in one direction), could you explain why reducing backlash in RA and DEC would help? Thanks
  13. The EQ3 DSO Challenge

    See any little green men? (My favourite whisky!)
  14. The EQ3 DSO Challenge

    A little green man going past last night in his flying saucer would have seen lots of scopes pointed up at him - a super night for AP! So time to revisit IC1396A, the Elephants's Trunk nebula, lit up by the nearby massive star. 18subs @ 480secs (approx 2.5 hours).
  15. The EQ3 DSO Challenge

    Thanks for the super fast reprocess Nige! I agree - the image that includes the 600s subs looks better. No sign of increased noise. My understanding of combining comes from a page on DSS theory (http://deepskystacker.free.fr/english/theory.htm) which states : ------------------------ Can I combine two (or more) resulting images? Absolutely, the square root rule applies with a small twist. When combining two images the SNR increases by 1.414 (square root of 2). If both images have the same SNR then this is the same as doing a single stack. That does not mean that the combination is giving the same image, just that the SNR will be the same. However if one stack contains more light frames than the other, the SNR of the two stacks will be different and the SNR of the combination will be lower than the SNR of a single stack containing all the light frames. Thus by combining the result of a 10x1 minute stack with a single 1 minute frame the SNR is roughly the same as the one obtained by combining 2 light frames. This is due to the fact that when combining two images the noise is additive and the best image is damaged by the worse image in the process. -------------------------- I must be missing the point (again!). Bob
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