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almcl

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Posts posted by almcl


  1. A little while since I saw this issue, but think it was using the 32 bit version of DSS and it was an indication DSS was running out of memory.  There was a work around that enabled it to use more of the available RAM (sorry, can't find a reference to that just now and it may have been for Win 7) but the long term solution was a 64 bit operating system and then to use the 64 bit version of DSS (presently using version 4.2.4 Beta, which seems pretty stable).

    Another possible cause may have been attempting to use drizzle, discovered that this was definitely not worth doing with my data.  

    @perdrix who is a member here is now the guru for DSS and can probably explain all in much more details and with much more authority!

    • Like 1
    • Thanks 1

  2. If the same line is present in several subs in the same place, it may be something out of frame causing a reflection.  Bright stars can cause this (Alnitak in Orion is a favourite) but can also result from inconvenient street lights, neighbouring (in)security lights, or even equipment LEDs showing up in the wrong place.

    In the case of your night1 image, the line points straight back at Deneb in Cygnus:

    662629388_Night1WWT.jpg.9d489dee38ad4da0953762e6514ddfad.jpg

    I haven't processed the other images but my guess is they will show a similar origin for the line.

    Not sure what the solution is, maybe someone else will comment?

    • Thanks 1

  3.  I use a SW 200p and the improvement in star shapes when I switched to guiding with an OAG was dramatic.  Prior to this I used an ST80, initially with a QHY 5l ii mono until the USB connector on that broke and then switched to an ASI120 mini mono.  The ST80's focuser was very floppy and that coupled with mirror movement was probably at the root cause of the poor guiding.  

    As to whether a 50 mm guide scope (likely focal length about 180 mm?) will do rather depends on your imaging scale.  I use a suitably adapted SW finderscope with the ASI 120 to guide my EQ5 with Canon + 200mm lens and it usually achieves just over 1" guiding.  As the 200 mm lens is imaging at a little over 4"per pixel, this is fine but when imaging with the 200p (.85" per pixel) on an Alt Az EQ6 it wouldn't (and didn't) do.  With the OAG the guiding is usually somewhere between .6" and .7" and on rare occasions drops below  .5".  This gives nice round stars.

    I use the dedicated Canon OAG and it certainly saves weight compared with the ST80.  Another benefit is that I no longer need a dew strip for the guidescope: the ST80 was an absolute dew magnet - an OAG doesn't need heating. 

    I've never had a problem finding a guide star with either camera (both mono) in any of the configurations, although focusing the guide camera is slightly more time consuming to start with.

     

     

     


  4. 13 hours ago, Adam J said:

    Its latteral chromatic aberation, a problem with all two element coma correctors.

    Adam, just thinking about that, the third image was taken without a Coma corrector yet it still has colour separation (admittedly in a different orientation to the other two) - so given that the only things in the image train are the two mirrors and the DSLR sensor, could it be something on the sensor, Bayer matrix or Baader filter, perhaps? 


  5. 2 hours ago, Skipper Billy said:

    reflectors give me a strange feeling that men in white coats might not be too far away 😉 

    I can identify with that one !

    2 hours ago, philhilo said:

    I am trying to get the hang of the collimation tool in APT 

    Hadn't thought of that, thanks! Will give it a try during the light nights.

    2 hours ago, philhilo said:

    Out of interest I can hear the mirror (or something heavy) shift when I move the OTA, do you get anything like this? I do use a laser collimator but it doesn't sit flush on the focuser and rocks about so is pretty poor. 

    I've changed the mirror cell mounting arrangements on my 200p (longer mounting bolts, stronger springs).  This helped with mirror flop/guider flexure but at the same time I also switched to an OAG so whether this stopped mirror movement or just concealed it isn't clear. I've not heard any movement - but am fairly deaf (and don't usually wear my hearing aids when out with the scope) .  I do find the scope needs both primary and secondary tweaking every time it gets mounted and put this down to the tube flexing.


  6. Thanks for running that through CCD inspector, Skipper Billy.

    I have often suspected that while I can visually collimate through the eyepiece (Cheshire, Concenter &c) hanging nearly a kilo of camera, home-made TEC cooler, coma corrector &c off of the slightly modified Skywatcher focuser probably undoes at least some of this at least as regards focuser tilt.  Although the CCDI tilt measurements don't look too bad?

    Does anyone know of a way to collimate with the camera in situ?  I've seen a couple of ideas somewhere but they were a bit vague on what to adjust if the out-of-focus star in the center of the field of view doesn't have the secondary circle in the middle (and having read Suter's Star Testing Astronomical Telescopes, am not sure that merely racking the focuser out a random amount is a completely valid test.)


  7. For a while now I have been concerned about multi-coloured stars turning up in my final, processed image.  Here's one such image (heavily downsampled) :

    2122609939_ASASb.jpg.5ded803a550871502fbfadca1c1df2ad.jpg
    and here's one of the stars from the upper left part:

    1558088874_mulicolouredstarsinthefinalresult.jpg.5988192b8c4e490397c25c93e016b9a4.jpg


    At first I thought this was just down to a lack of processing skills on my part, but then I noticed that individual raw subs also had some colour separation:

    779454071_comacorrectorCLSfilter.jpg.d02d5e093510e8bd48a0aefbaf3cba24.jpg
    and wondered if this was a feature of the SW Coma Corrector which I use with my slightly modified SW200P.  So last night as it wasn't going to get fully dark, I removed the coma corrector and attempted to image with just the camera sensor and main and diagonal mirror in the light path.  The results (which were tricky to obtain - the OAG really picks up the coma stars big time) surprised me: there are still odd coloured fringes to the stars:

    675684782_nothingbutthemirrorssensor.jpg.10444cdd3206b5c438d691ee5af1b166.jpg

    So what's causing these coloured fringes?  Is it chromatic aberration and if so, where's it coming from?  

    Or is it a characteristic of the astro modded Canon 700 (with the Baader filter that Juan at Cheap Astro Photography supplies)?

    Any thoughts on what the cause might be and how to mitigate it would be most welcome.


  8. Once you put some files (bias frames would be a good choice) in the Main Group, a new tab will become available, 1st Group,  if you put your lights and flats in this group  a further group tab should open.

    However, you may find stacking different length and ISO subs altogether doesn't produce a very good result and it may be better to stack the short  subs and long subs separately and then selectively combine them in your image processing software, maybe using layers and an eraser tool.

     

    • Like 1

  9. 29 minutes ago, SteveBz said:

     I might download a version of StarTools, it appears that you can get an evaluation version.

    If you decide to try StarTools, the Release Candidate versions (RC) are stable and have all the latest bells and whistles.  You can do everything a paid-for version does, except save (but you can take screen grabs).  There is a bit of a learning curve but several SGLers use it rather successfully.

    • Like 1

  10. 6 hours ago, SteveBz said:

    Do I need to 'Demosaic'?  I'm not really sure what that does, but maybe I need to do it.  I'm also not sure which of the three images in my fit is the R or the G or the B, is it just 1 2 3 = r g b?

    The only stacking program I use (DSS) doesn't use the term demosaic, so not absolutely sure about this, but if it's synonymous with debayering, and you are using a DSLR then, yes it has to be done. DSS will do this automatically with RAW files but the correct Bayer pattern needs to be selected (for the ones I've encountered it's RGGB).

    The FITS planes in Fits Liberator are, as you say, Red, Green and Blue. 

    Your latest image has got colour, although it's quite hard to see until it's been stretched (image below is a crop of your central area which I stretched and colour balanced in StarTools).  As expected from the UHC filter, you've got blue/green and red, but of course no yellow.  Nice round stars and several of the smaller faint fuzzies, too.  

    r7_pprgb.jpg.ad8e1a2f67947d1a71ba23a7213ee717.jpg

     

    • Like 1

  11. 6 hours ago, SteveBz said:

    Ohhh kay... so is that what is called flexure? I see from your signature that you use an OAG with a ZWO ASI120, I use the QHY5, but I think they're broadly similar apart from pixel size (yours is finer).  Do you have difficulty finding guide-stars? I have been thinking about getting a low profile OAG for my Newtonian f5 (is yours similar?), but it seems like a vanity rather than a necessity - and I particularly don't want to buy a new cam at this stage.

    Yes, flexure is the term.  My rig suffered from it quite badly (had a thread about it somewhere but can't find it at the moment). I switched to a Canon specific OAG and the improvement in star shape was dramatic.  Originally I used a QHY 5Lii m but the USB socket on the back wasn't strong enough for the heavy and inflexible QHY supplied cable and it became unreliable and eventually broke (there's a thread about that somewhere, too).  I then switched to the ASI 120 mini and found it to be very similar to the QHY.  It has never failed to find a guide star (YMMV) in the two years I have been using it. If your QHY is OK, I think it would work well with an OAG.  

    Yes, my Newtonian is (or was) an F5.  I have since mucked it about a bit (shortened the focus tube to stop it intruding in the light path, moved the mirror cell when a Baader click lock was added to better centre the Coma Corrector, baffled the main mirror to remove the mirror clips from view, added a bottom fan to stop the main mirror dewing up, replaced the single speed focus knob with a Lacerta 10:1 geared version &c &c).

     

    6 hours ago, SteveBz said:

    I can try the dithering quite easily, how big a dither should I make (I think from memory it's .5x to 5x)?

    Opinions vary a bit on how big a dither to use, some say big (>20 pixels) others say 5 or 6.  Getting your capture program and PHD2 to co-operate is the trick. I am currently using between 5 and 12, but again YMMV.

     

    6 hours ago, SteveBz said:

    I can probably also try the Sigma clip, again, let me ask, what parameters do I need?

    I think I left DSS at the defaults (Kappa 2, iterations 5) but Vlaiv had a thread in which he suggested other values (with convincing mathematical arguments) but they didn't work as well for me so I reverted.

    By the way, your latest stack is beginning to look quite nice - hours of processing fun to had during the light nights of the summer :-)

    • Like 1

  12. 9 minutes ago, SteveBz said:

    Do I take it from your signon, that your name is Al?

    yes, sorry - my sig has lost a bit somewhere - it's Al.

    I see what you mean about calibration, and now I've looked a bit closer, I think there may be some walking noise (the yellow rings around some artefacts):

    Untitled-1.thumb.jpg.db517aaf617a3810822e0dcbf9325091.jpg

    I can see the wobbly stars, are you sure you got all the rogue subs out of the stacking list (my favourite is missing one satellite trail...) if you are sure, then try stacking with a Sigma Clip routine and see if that helps?

     


  13. Morning Steve

    I got the histogram from Corel Photopaint.  Unfortunately, I don't think anybody else on SGL uses this, so probably not a lot of help 😞

    Also am only a Windoze user, so not much useful advice to offer about Linux based processing.  I did try FITS Liberator but found it very difficult to get reliable stretches (and the interface was extremely buggy) so ended up as a StarTools user, but one suggestion from the StarTools forum which might be worth a look, is to use your filtered data (from the UHC stack) to create a Luminance dataset and then to take some unfiltered images and uses these as RGB data after a suitable wipe to remove any light pollution.  Process the Luminance stack for max detail and then combine it with the RGB to restore the colour.  I barely know how to do this in ST and have never used GIMP but guess it must be possible?

    I think stretching the filtered data alone in whatever program may not yield 'natural' colours as so much of the spectrum is missing - my 'City Lights Suppression' filter (Astronomik CLS CCD clip filter) while great at getting rid of sodium lamp skyglow does also mean that I never get any yellow stars!

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