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philherbert

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About philherbert

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    Nebula

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    SkyWatcher ED100
    SkyWatcher HEQ5 Pro
    Canon 350D (unmodded)
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    Leicestershire

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  1. I have a SkyWatcher ED100 and currently use a ZWO ASI1600MC-Pro so no filters to worry about. It sounds like a fairly slow process Olly - either taking subs or using some kind of live view while manually adjusting the focus to minimise the FWHM? Do you find this more accurate than a B-mask?
  2. Hi, I've been imaging for a while now, and only ever used a Bhatinov mask to get fairly good focus. Recently I have been wondering about getting an auto focusser. I have two questions: 1. Is an auto focusser worth it - the added complexity and things to go wrong? 2. How accurate is it? I use APT with the Bhatinov mask and focussing aid, but the reported 'accuracy' varies substantially. And yes, this is after waiting for the scope to cool down. I fear that an auto focusser could be badly confused by this (presumably caused by the seeing) and end up getting it wrong? Thanks,
  3. I'm no expert, but could it be a very slight gap allowing light to leak into the OTA somewhere when in a particular orientation, perhaps in line with nearby lights? The fact that you can apparently see stars in the background is also odd - are they the right stars in the right location (can you compare to any previous subs of the same target)? Be worth checking that everything is tightly coupled.
  4. I just wanted to close this topic off, in case anyone is desperate enough to read to the end! I have spent nearly two months trying to sort the problem out, and was starting to question my sanity, but in the end the camera supplier (FLO) were good enough to provide me with a replacement camera to test. I'm pleased to report that the inverse vingetting and curvy lines that were visible in the 'background' of the stacked images have all gone, so I am concluding that there was some kind of problem with the camera (I have been careful to change nothing else in the imaging train or software se
  5. Well I tried to test my first hypothesis (whether there is any stray light in the subs) but didn't end up showing anything useful. I have since been exploring ways of creating a synthetic flat which should at least remove the dust shadows. Still a work in progress. It shows promise (the dust shadows appear quite well) but it is a pain getting rid of the stars. I'm trying various techniques out but would be interested in others techniques for synthetic flats. Phil
  6. Well I've done the new darks being careful to block out any sources of stray light. I've also taken a new set of flats (the dull overcast weather is useful for something). However there is minimal difference when pre-processed, and I still end up with the reverse vignetting. I'm now wondering whether the problem might lie with the original light subs instead of the calibration subs? (Ok, there were some minor issues with the calibration subs, including the need for dark flats, that I believe I have now sorted out, but I still have the original problem.) My theory is that the flats a
  7. My scope is a refractor with a focal reducer. I have just checked and there was a very slight amount of slack in the connection between the focal reducer and the main scope, so conceivably this could have allowed a small amount of light in, potentially affecting the flats and possibly the original set of darks. It may be that my previous approach that worked fine with an old DSLR just isn't rigorous enough for such a sensitive CMOS sensor. I'll take another set of darks tonight (in the dark so that there is no stray light). I'll also see if I can minimise any stray light and take a new se
  8. Yes you make a good point about not being able to isolate the problem area from the amp glow, so that is not an option. The original darks you have analysed were taken with the scope lens cap on, but in daylight (on a cloudy day). This was not ideal of course. The second set of darks that I mentioned were taken in the evening with the lens cap on and a large dark towel over the telescope as well. I have looked at these darks and there is only the amp glow, no sign of the central signal. However after processing I am still left with the reverse vignetting from some kind of over correction.
  9. Hi Vlaiv, thanks for your analysis! I have checked the other darks, and there are certainly some variations between them. I have also compared them to another set of darks that I took under much better circumstances and there is much less variation between them - I used 'blink' to compare them. Unfortunately, processing again with this better set of darks still leaves the inverse vignetting. I was thinking - if the darks are over-correcting, can I 'reduce' the effect of them somehow (perhaps using Pixinsight's PixelMath) do you think?
  10. Hmm, I've created a set of dark flats / flat darks with same temperature, bias, offset and exposure duration as the flats, just without the light :-) . I've just run them through with Deep Sky Stacker and get no appreciable difference - the vignetting is still over correcting in the centre of the frame. Here's a link to a dark flat in case it is of any help: https://www.dropbox.com/s/tnwdg51aevtir94/2018-01-31_21-20-25_DF_1.55s_G139.fit?dl=0 I've stacked with lights, flats and dark flats (no difference), and also with lights, darks, flats and dark flats (still no difference). I've even th
  11. Thanks to all for the suggestions. I'm just creating some flat darks (never used those before) matching the flats and will report back...
  12. Sorry, my bad. Here you go. Light, dark, flat, bias in that order. Phil https://www.dropbox.com/s/4erb24i7brxbsq9/2018-01-07_18-44-14_L_180s_G139.fit?dl=0 https://www.dropbox.com/s/5w1q7rmm6siyvdo/2018-01-14_10-38-21_D_180s_G139.fit?dl=0 https://www.dropbox.com/s/49hh0d4qoo8y3u7/2018-01-21_12-23-59_F_1.55s_G139.fit?dl=0 https://www.dropbox.com/s/yjp7prj6gcrbf4v/2017-12-30_13-12-09_B_0.001s_G139.fit?dl=0
  13. Sure. This are examples of the light (top left), dark (top right), flat (lower left) and bias (lower right). All are raw subs, just auto-stretched with the STF tool.
  14. Hi All, I have recently converted from an old Canon DSLR to a ZWO ASI1600MC-Pro. The individual subs look great with the new camera, but I am having seemingly insoluble problems processing, so I need the assembled wisdom here! The first image shows a single sub on the left (auto-stretched), and the result of stacking some 25 subs on the right, combined with flats. The flats have corrected quite nicely for the dust doughnuts, but given me inverted vignetting. (I should say that I have tried processing with darks and bias as well, but the basic problem of the reversed vignetting remains. Pr
  15. Eureka! I did the restore default settings, and then went through the recommended settings. The one that I didn't recognise says: You are using bias frames >Set the black point to 0 to improve calibration I wasn't sure whether I had set this before, so had a quick Google. That took me back to a four-year-old thread where "dph1nm" said: "Using this (with bias frames) kills my Canon 1000D reductions (flats no longer work), so I always have this switched off." And sure enough, switching this off has got my stacking almost back to normal. Now I think I
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