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About IanL

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    Sub Dwarf

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    Developer of the Imaging Toolbox.
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    Near Colchester, Essex, UK

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  1. The mesh effect is a pretty standard part of the diffuser on these panels. Really the only test that matters is to take some flats and check them before you start tearing it down.
  2. OK I was doing some flats yesterday which weren't satisfactory. There was a light band across width of the frame (about 5% of the total height of the frame), followed by a narrower dark band and then a lighter band shading in to a more 'normal' looking flat. This was across R, G, B and L filters. I also thought it might have been daylight leaking in so made a cardboard shield to block/reduce any light coming in from the narrow gap around parts of the observatory wall/roof meeting. Made no difference. I had set the flat panel to 255 (maximum) brightness and had calibrated the exposure time t
  3. Other light source adding to the flat maybe - daylight or a street light?
  4. You may have done this already, but the first thing I'd try taking a flat (call it "A"), taking a second flat (call it "B") then physically rotating the panel 90 degrees and taking another one (call it "C"). Then: - Compare the median ADU values of "A" and "B". They should be pretty much the same give or take a few ADU or tens of ADU. If they're markedly different then you either have a problem with the light source (flickering at a high frequency that is sufficient to create different brightness levels from frame to frame and may appear as a gradient), or perhaps the camera/electronics b
  5. I can only speak for the earlier versions of the 1600, i.e. the newer "Pro" version has onboard RAM to overcome these issues as it speeds up the readout greatly. With the older versions of the 1600 there is a change in readout modes for exposures longer than 2 seconds (if using USB3) or longer than 5 seconds (if using USB2). Apparently this is to reduce the noise in longer exposure images but ZWO never really explained how or why. Shorter exposures below these limits effectively stop the exposure at read-out, but longer exposures read out progressively which means that pixels at the top
  6. It's walking noise. You need to dither between subs by about 15-20 pixels. (I.e. Re-point the scope slightly for each exposure). If you're guiding then it's easy as there are settings in the software to do it automatically. If you're just using a tracking mount and no guiding, then you're going to have to do it manually - maybe re-point every two subs or so - you just need to nudge the RA and Dec axes a small amount in random directions each time. The problem is that the camera's pixels all have slightly different responses to light, plus there are other sources of noise. Over the course
  7. Pointing along the line to the centre (outwards in corner/edges) = too close. Pointing 90 degrees (crossing) the line to the centre = too far. \ | / - x - = Too Close / | \ / - - - \ | x | = Too Far \ - - - /
  8. a) There was a small error (which I corrected in a follow up post), the guiding calculation should have read "(5.2µm / 400mm) x 206.3 = 2.67 arcseconds per pixel", i.e. result was correct but mistyped the camera pixel size. Not relevant to the question but just thought I'd clear it up. b) "1.5 times" was perhaps a poor choice of words. The imaging resolution is 1.5 times better than the guiding resolution, i.e. there are 1.5 times more arcseconds of sky on each guider pixel than on each imaging pixel. So pedantically you are correct, but hopefully the point is clear that your guiding reso
  9. Reflection of an external light source that changes as the scope tracks?
  10. If you're looking to compare noise, e.g. using patches of the background sky, use MAD (Median Absolute Deviation). It is a much more robust measure than StdDev. For example removing outliers (e.g. hot pixels) will have a significant effect on StdDev whereas it won't on MAD and thus allows you to compare the underlying noise distribution of the before and after images.
  11. The manual is here: https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.baader-planetarium.com/en/downloads/dl/file/id/175/product/2856/instruction_manual_for_all_baader_diamond_steeltrack_bds.pdf&ved=2ahUKEwjcipWQhYbqAhVKTcAKHZDcAEoQFjAAegQIAxAC&usg=AOvVaw1GJ5_6SdkVmNgNQpbo9EfL Read page 10. The pressure screw is set for 6Kg (imaging) and may need slackening slightly for visual. It is the single hex head in the centre of the drive base. Don't mess with the other screws.
  12. I don't know about the ASIAir but I assume it uses the same process. Basically you take an image, rotate the mount 30 (polemaster) or 90 (sharpcap) degrees in RA and take a second image. The software identifies the corresponding stars in both images and uses geometry to work out where the centre of roation is (i.e. where the RA axis is pointing on the sky). Using plate solving it works out where the NCP is in the image and directs you to adjust the mount until the NCP and centre of rotation match.
  13. Again, yes a polarscope can be misaligned and will cause issues. A Polemaster does NOT depend on being well aligned though. The software determines the centre of rotation in the series of images, so any misalignment is automatically taken to into account. (Same for Sharpcap). That is why they are superior at alignment. Yes you are correct that if you have a perfect polar alignment, an accurate home position and zero cone error the main scope should be centered on the NCP. In fact the easiest way to check your cone error is to take an image of the NCP (once polar aligned and homed). Plate
  14. You're confusing three different concepts: 1. Polar alignment refers to the alignment of the RA axis of the mount so that it is parallel to the Earth's axis of rotation. Neither the mount's home position nor the scope's cone error have any bearing on this. - You can polar align using the mount's polar scope. This is subject to a number of cumulative sources of error; how well the polar scope and reticule are aligned to the mount's RA axis, and your ability to precisely align Polaris on the reticule over several steps to find the appropriate hour angle. Usually this can be done well enoug
  15. This month's public lecture will be given by Ian Lauwerys on the subject of radar meteor detecting. We will look at the practicalities of building your own back-garden meteor detector, delve in to the murky world of top-secret spy installations and cover some of the science behind meteor detecting. The talk will be presented live via our YouTube channel (details below) and will also be available for replay later. The downside if that you'll have to supply your own tea and biscuits, but on the plus side we'll be able to give a demonstration of a meteor detector in action. The stream w
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