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About dph1nm

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  1. dph1nm

    Historical imaging data ???

    http://archive.eso.org/dss/dss gives you access to scans of the Palomar and Siding Spring photographic Schmidt surveys, NIgelM
  2. Flats do not just correct for optical effects, they also correct for variation in the QE of each pixel on the chip, and that obviously depends on the spectral distribution of the incoming light. If all pixels had identical spectral response that wouldn't matter, but at some level they don't. For instance, CCDs are often thinned to improve response to blue light, but if than thinning is not uniform there will a be a different response in different parts of the chip. If you illuminate with e.g. an Halpha source you will not see these variations. NIgelM
  3. It is what you might call a 2nd order effect, but the response of a CCD is wavelength dependent, and this dependence can vary slightly between pixels and over the chip (for thinned chips you can get fringing of course). As a result, the flat correction required for, let us say, an emission line source would be different from that for a blackbody source. But I admit it is tiny effect (although maybe not so tiny for fringing). NIgelM
  4. Hmm - I think scattered light getting into the flats might limit the ultimate precision. Also the spectral difference between the astrophysical source and the light source used for the flat. NigelM
  5. I don't think there is anything wrong with the theory, however I suspect there are at least two practical problems with this: (1) it would take an unfeasable length of exposure time to reach the same S/N, (2) it would require the LP to be spatially flat to high precision and require your flat fielding to be correct to high precision (at least at the scale of the IFN). NigelM
  6. dph1nm

    Second hand camera.

    I think the shutter on the 1000D, although electronically controlled, is mechanical, and I believe they do fail. NigelM
  7. On an EQ mount the star alignment does not affect the tracking, only the polar alignment does that. NigelM
  8. Looks more like fringing to me. NIgelM
  9. dph1nm

    Synguider help

    I think mine did that when I tried to run it off 6V. In the end I used 9V and it was much happier. NIgelM
  10. The 12S Quattro comes with a Losmandy dovetail - so it is obviously possible for Skywatcher to produce suitable rings. NIgelM
  11. dph1nm

    EQ8 and Focal Length

    I have successfully imaged unguided for 2mins at 0.6"/pix with my EQ8 (with PPEC turned on). NIgelM
  12. dph1nm

    How to Get Less Noise

    There seems to be some confusion in this thread. So the only real difference between ISO400 and ISO1600 is that the read noise is lower at ISO1600 (for the Canon 1000D) and the dynamic range is greater at ISO400. The amount of light you collect is the same at either ISO. So to overcome read noise you will need somewhat longer subs at ISO400 than at ISO1600. However, If your subs are already long enough to overcome read noise then you may as well use ISO400 to get the higher dynamic range - but the final signal to noise will be the same for either ISO, if your total exposure time is the same. NIgelM
  13. I don't think DSS will stack images (whether flats or lights) of different exposure times. You can get round this by editing the images' properties in DSS and setting them all to the same exposure time (might have to be 1 sec, as I could never get the editor to accept shorter times). NIgelM
  14. I believe that if you do a 3 star align these numbers are re-calculated. Previous values are only applied to 1 and 2 star alignment. NigelM
  15. dph1nm

    SkyProdigy is slowly dying

    Yes, my SLT (which I have had for many years) did/does this. Still works though - even though it slows it still gets the coordinates right! I believe I read somewhere that the problem is the brushes on the motor getting dirty, but I have never tried to clean mine, so I cannot verify this. It does sometimes help if you run it round and round at the highest speed for several minutes though. NigelM

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