Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.



Advanced Members
  • Content Count

  • Joined

  • Last visited

Everything posted by dph1nm

  1. Here is an interesting link https://www.star-watcher.ch/equipment/measuring-periodic-error/ which suggests that you are going to notice trailing after about 20 secs at your focal length. Having said that, looking around the web the reported PE of the star adventurer varies wildly, and the one in the link seems particularly bad. So you are probably going to have to measure it for your own mount. NigelM
  2. Nothing obvious in Pan-STARRS, SDSS or DECaLS surveys at this location. NigelM
  3. I use a Skywatcher 12" F4 for imaging on an EQ8, also with ~1" pixels. Excellent scope. I also used a 10" F8 RC for a few months last year (~0.6"), which was also very nice, and despite the theory, even in 3-4" seeing, those smaller pixels give a rather pleasing image on small objects. However, in my opinion aperture always wins, and I wouldn't go back to less than 12" now. NIgelM
  4. Pointless doing this in DSS. You just end up subtracting the bias from the bias! Works perfectly fine if you just ignore darks completely. I just use lights, flats and bias. NigelM
  5. The selection of RB Digital magazines available to you is dependent on your local library (well, the library you subscribe to, to be precise) - mine only has All About Space. They used to have Sky At Night but dropped it a couple of years ago. NigelM
  6. Here's a tip. Do not go straight to "Stack checked pictures", instead use "Compute offsets" first. This will then show you the score, number of stars detected, dx dy and rotation offsets, sky and seeing for each frame. If dx and dy are not given values then that frame will not be used in the stacking process - you can then try and work our why. There must be at least 8 stars (in common) for frames to be registered by the way. - this is usual reason for failures. NIgelM
  7. http://archive.eso.org/dss/dss gives you access to scans of the Palomar and Siding Spring photographic Schmidt surveys, NIgelM
  8. 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
  9. 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
  10. 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
  11. 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
  12. I think the shutter on the 1000D, although electronically controlled, is mechanical, and I believe they do fail. NigelM
  13. On an EQ mount the star alignment does not affect the tracking, only the polar alignment does that. NigelM
  14. 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
  15. The 12S Quattro comes with a Losmandy dovetail - so it is obviously possible for Skywatcher to produce suitable rings. NIgelM
  16. I have successfully imaged unguided for 2mins at 0.6"/pix with my EQ8 (with PPEC turned on). NIgelM
  17. 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
  18. 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
  19. 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
  20. 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
  21. You can safely ignore the NPE (and CE) messages. They shouldn't happen if you do a three star align anyway (as they are calculated afresh when you do one), only for 1 and 2 star (as you need at least 3 stars to calculate NPE and CE). NPE shouldn't change anyway, as it is the orthogonality of the mounts axes. CE is the cone error, which depends on how the scope is fastened to the mount, but I don't image that will alter unless you change the scope. However 39' is quite an offset for the polar alignment, especially if you are trying to image. NigelM
  22. Using the superpixel debayering mode in DSS might fix the problem (which is almost certainly due to the stars being out of focus). Nigel M
  23. How? These mounts do not have encoders so cannot know where they are when you first switch them on. The only possibility I guess is that they have a home switches on the axes, but my (admittedly old) HEQ5 doesn't (although my EQ8 does). NIgelM
  24. Hmm - not sure this makes much sense. As I understand it the SQM already has a 'visual' broad-band filter, and the results are calibrated to work for that. So if you stick another filter in front surely the calibration will not be right? I mean I could stick a neutral density filter in front and get as faint a sky as I liked. NIgelM
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.