Jump to content





  • Posts

  • Joined

  • Last visited

Everything posted by philherbert

  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, Phil
  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 settings, so I'm 99% sure that this is the case, although I don't know enough about the camera to work out what kind of fault could have caused it). To be more accurate there remains a little inverse vignetting, but ABE / DBE in PixInsight deals with it pretty well. In the end it was the curvy lines in the background that couldn't be dealt with through any ABE/DBE or alternatives that convinced me that the camera was to blame.
  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 are actually working correctly. My very basic test for this is whether they compensate for the dust shadows, and they do. If this theory is correct, and they are working properly, then they are also correcting for the vignetting. Which leads me to think that whatever remains after pre-processing is some stray light that was collected during the light subs. (When I say stray light, I mean not signal from the target, and not noise inherent in the sensor etc, so sky glow / street lights / house lights / internal reflections). Apart from re-taking the lights, and trying to minimise stray light, I can see two options: (1) Work out a way to test whether there is any stray light in the subs or (2) Create a synthetic flat. For (1) I haven't yet thought of a way to tell. There is some noticeable difference between the first sub and the last sub, so I was wondering about subtracting one from the other, once aligned, to see what remains as perhaps a difference in the stray light at the time? For (2) this article http://trappedphotons.com/blog/?p=756 is very interesting. Has anyone tried anything like this? Phil
  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 set of flats. And then I'll report back...
  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. Here is one of the better darks: https://www.dropbox.com/s/uj6joog55nfzgtq/2018-01-21_17-49-53_D_180s_G139.fit?dl=0 (By the way, for anyone else with similar issues, the bright central area was not really visible in the original flats until it was debayered and then given a very strong stretch - it didn't show in the grey version of the dark. In reality it only showed in a few of the original dark subs.) So in summary I have a fairly good set of darks (unless someone can show me otherwise of course!), and using dark flats I get slightly better calibration than using bias frames, but I still get inverse vignetting. The effect is shown below: With PixInsight and the AutomaticBackgroundExtraction tool I get a result looking like: The left-hand image shows the removed signal; the right-hand image the result. As you can see it leaves a 'halo' around the centre of the image. It also leaves the snaking lines in the background which I think might be symptomatic of another problem. Any takers? I'm running out of idea! Thanks, Phil
  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 thrown the bias in there as well as an experiment (no appreciable difference).
  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. Processing was done in Deep Sky Stacker, although I get the same results using PI and the BPP script). I initially thought this was down to using the wrong ADU values for the flats, so I've tried various from 5,000 up to 30,000 in 5,000 increments, but nothing improves - the higher the ADU the worse the effect seems to get. I've also tried different techniques for taking the flats - grey skies (easy at the moment) with t-shirt layers in front, or a tablet screen on white. Flats are seemingly ok - here is an individual sub on the left and master flat on the right. OK, they are rather brownish, but apart from that they look ok to my (DSLR-attuned) eye. Different ADU values seem to fail to correct for the dust doughnuts, as well as making the vignetting worse. I have one further thought / problem to add. The over-corrected centre of that processed image (top, right-hand side) shows some odd details. Here's a zoomed version. There are fairly broad swirly lines showing up in there. Actually the lines are across the whole image, but most visible in the centre where the vignetting shows it up. My only thoughts are that this could be condensation or similar? Might this account for the flats not correcting properly? As I said I'm using the ASI1600MC-Pro, and have it set to cool to -20C for all lights, darks and flats. I've not encountered a problem like this with flats failing to work so miserably, so I'm after any and all knowledge at this point. To a fair extent I can take out the vignetting with ABE/DBE, but that then leaves me the dust doughnuts. I really don't want to have to 'edit' my pictures to that extent, and feel that the flats should take care of the vignetting. Thanks for looking. Phil
  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 have to take the flats in the right way since they aren't correcting 100%, but the bizarre colour correction is largely sorted out. Thanks for your help and suggestions! Phil
  16. I've left it all to DSS - just providing it with lights, flats and bias. However I do agree that DSS has got confused! Is there any way to reset the settings? I've run out of things to try!
  17. I've retried taking the flats many times and still get the same odd results. I'm pretty sure focus hasn't moved much - the flats looks very similar to previously. I'd like to think that a small shift in focus wouldn't produce the bizarre results (although in AP nothing would surprise me now).
  18. I took the flats using AV mode on the Canon as I have always done. The exposure length was 1/180s which is slightly shorter than previously but as expected (the LPF would have required a slightly longer exposure due to the restriction in light I assume). The histogram peaks were well within the histogram. I did take the flats in the daytime, but I have done that always in the past as well without any issues. I stopped using darks a year or so ago, since they seemed to make little if any difference once dithering in my guiding setup. Everything you have said is good advice, but I'm struggling to work out why the master flat is coming out so differently now. I suppose I might have to reintroduce the LPF and see if things work as they used to? I'm also wondering if I have a silly setting in DSS but for the life of me I can't find it! Phil
  19. Hi Experts, I have been imaging for a year or two, gradually increasing my skill levels (or so I thought). I use a SkyWatcher ED100 on an HEQ5-Pro, and an old Canon 350D for imaging (unmodified). I'm also guiding with a QHY 5-II through the SW finder scope. Everything has been fairly ok until a week or so ago when I removed the SW LPF that I have been using. The individual subs appeared to have more detail in them with a 300s exposure than previously, and I thought I would be able to process out any light pollution using PixInsight. I use DSS to stack and combine (I really must get around to learning how PI does the integration). However it hasn't worked out like that. I realised that having changed the imaging train, I would need to take new flats. However no matter how I take the flats (using a table over the end of the scope, using an LCD monitor showing white, or using the sky through a white t-shirt), I get disastrous stacks from DSS, badly over corrected with a lot of extraneous colour (see first attachment below). I assume it is down to the MasterFlat that DSS creates and uses. The MasterFlat used to look like the second attachment, but now look like the third attachment. Have I simply over exposed now that I don't have the LPF reducing the light getting to my camera, or have I tripped up another way? In case it helps, here's also a single light sub as the fourth attachment, and a single flat as the fifth attachment that went on to produce the horror that is the masterflat with the red ring! Any thoughts welcome - this is driving me nuts and there could be clear skies coming up! Phil
  20. I'm more interested in what to get than the budget, although it is of course a factor (it looks like £2k - £3k would be necessary). I'm hoping that a cooled CCD would give me a fairly good step forwards, especially on fainter DSOs that the 350D struggles with. I'm quite seriously considering a colour CCD since I don't fancy the additional complexity of mono with filters, and imaging time is hard to come by so I'm not sure I'd ever be able to complete an LRGB image! How do people manage 10 hours on one target? I barely manage 2 hours!
  21. Thanks Jules. After a couple of years of tweaking I think I've got about as far as I can with the equipment I've got...although if you think the combination can deliver more then I'm happy to hear it! Phil
  22. Hi All, I have been imaging for a couple of years now with an ED100 (with 0.85 focal reducer) on an HEQ5 Pro mount, guiding with PHD2 via the guide scope and a QHY 5-II. My camera is an unmodified Canon EOS 350D. I'm getting some reasonable results now (see attached my best recent pictures), but as always with this hobby I'm craving better images! What do you recommend as the next step? I'm initially thinking of changing the old Canon to a new CCD, but I wonder how good the HEQ5 Pro mount is (I'm probably feeling negative about it after some dodgy guiding on recent nights with high cloud drifting over, or mist coming and going). So what's the collective advice on the next step? Also I'd be interested in suggestion on the best CCD to go for with this setup. Thanks for reading, Phil
  23. Hi Ian, I'm a few weeks ahead of you in my efforts in the same area. Plate solving - as long as you take the coordinates from the mount, solving works pretty well for me - 40 seconds at most. You can test this on an image in advance to be comfortable it stands a chance of working. Focusing - simply put you don't. But turn the focusser a quarter in one direction, take another image, and see if it looks closer to focus. If not you should be able to estimate whether it was in the correct direction or not. I'd recommend not using the Bhatinov mask until you are relatively close to focus by eye - it's best for fine tuning. PHD2 calibration - you will see if moving the guide star while it is calibrating (although you won't see the scope move). It makes a number of moves N, then S, then W and E (I think in that order). If you've got your step sizes reasonably set up, it works fine. Good luck with the clear skies tonight. Wrap up warm! Phil
  24. Many thanks for the suggestions. As DanL says, there is no live view on the 350D, but you are right that I do need to make sure I shut off the image preview! The AC power supply for the camera doesn't need a battery in there. I've also disabled the settings that allow for USB ports to be suspended - it might have been something like that causing the symptoms I had, although it was odd that the camera seemed to get into a confused state! I'll try again if ever there is some suitable weather!
  25. Hi, I'm slowly working my way through the learning minefield of astrophotography. My latest unexpected problem is my old Canon 350D (unmodified). Having had a few times when it just stopped working, and found it was the battery dying, I've started using a mains power supply. However I am still getting problems. My setup is using APT to control the camera, with a separate USB-to-serial cable providing shutter control. It works fine but after around an hour of usage the camera just stops doing anything. Powering the camera off and then on again doesn't seem to help at this point. Of course, it generally takes me around an hour to do the alignment, focus (manually with Bhatinov mask) and decide on a target. At which point the camera just gives up the ghost. I wondered if it might just be the cold and / or damp getting to it? Any thoughts or experiences to share? Thanks, Phil
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.