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Posts posted by BrendanC

  1. The Horsehead and Flame Nebula.

    * 6:40 hours of H-Alpha from 80x300s subs
    * 4:54 hours of RGB at ISO800 from 38x300s + 4x240s + 16x180s + 20x120s subs (shorter subs while object going over light polluted area, progressively longer as it moves up/across the sky)
    * Bortle 4, Moon average 5% phase, 15° height
    * 25 flats, 25 dark flats, 50 darks
    * Sky-Watcher 130PDS with primary baffle, NEQ6 with Rowan belt, EOS1000D minus IR filter, 7nm H-Alpha filter, 0.9x coma corrector, APT, PHD2, APP, StarTools, Photoshop, Topaz DeNoise AI


    • Like 10
  2. Just bumping this one gently to see if anyone can confirm that yes, I should really ideally be exposing Ha subs until the histogram reaches further across to the right, between 1/3 and 1/2 way across. I can see that it's going to be a balance between light capture and thermal noise, but all I need to know is, should I be doing this? I think the answer is yes. If someone could just say 'yes', I'd feel much better.

  3. Yep, I know I'm losing resolution. It's just a way of being able actually to do something during those periods when the skies are clear and the Moon is inevitably big and bright!

    Thanks for this, and I think I've seen that Robin Glover presentation on YouTube. I went through a load of his stuff to arrive at 240s or 300s being optimal for my use case for RGB subs, but I'm just not sure how this affects Ha subs.

  4. Hi all,

    I've started doing some Ha imaging with my trusty little modded EOS1000D to create HaRGB images and getting some decent results (to my eye anyway).

    However, I've been thinking about exposure times and histograms. I have a darks library that goes up to 300s sub lengths, and so I've been doing Ha subs at 300s. But, I've noticed that the histogram is very much packed to the left, obviously because of the less light let through by the filter.

    So, I know a lot of this game is 'try it and see' but does anyone have a view on whether I could/should consider longer sub lengths when shooting Ha, to bring the histogram further to the right and improve SNR? And presumably if I do that, I'll also need to create a darks library for them (which would be painful, creating a darks library for each temperature at, say, 600s+)?

    Also, is there any 'mathematical' way of estimating by how much the sub length should increase? I did once come across a page that said a 7nm filter lets through X amount less light so you need to increase your sub lengths by X to compensate, but have never been able to find it since.

    Thanks, Brendan


  5. Thanks! I'm pretty accurate with my polar alignment, at least according to Sharpcap.

    This is by no means a showstopper. I'm getting results I'm pleased with. It's just one of those niggles that you'd rather not have and after a while you decide to try and do something about it, if you know what I mean.

    I think I'm going to look into cone error, using the ConeSharp utility.

  6. Works like a charm! I'm going to test it a lot more before I let it loose on my files, but I've run a few already, made sure it can distinguish 1C from 10C etc, and it's really fast and does exactly what I want.

    The only request is, could the folders just be called eg 12C rather than Temp_12C? It would just fit into my system better. Very small thing really, but while I've got the chance, it would be great to get this bit sorted.

    Thank you again! Really, really appreciate it. :)

  7. Hi all,

    When I stack images from a session that involved a meridian flip, there's always a slight rotation in the pre- and post-flip images.

    I don't mean the 180 degree rotation. I mean there's a misalignment, so that before and after are a few degrees out from each other. It should ideally be pretty much exactly a 180 degree rotation, but it never is.

    This isn't a huge problem but it bugs me, especially when I want to make as much of the image as possible for large nebula etc, which I lose because I have to crop out the artefacts around the edges.

    I've looked around and found this thread which, after much discussion and diagrams, didn't really end up with a definitive answer or recommendations on how to fix it: https://stargazerslounge.com/topic/280998-rotation-after-meridian-flip-why/

    Is this because my scope isn't completely straight on the mount ('orthogonal' is the word, I believe)?

    If so, what's the best way to fix it? Would ConeSharp help, for example? (see https://www.sharpcap.co.uk/conesharp)

    Thanks, Brendan

  8. Thank you Alan, that's very kind of you! I daresay other people might find such a script useful too.

    No need to go ahead just yet (unless of course you want to), let's see if anyone has something 'pre-baked' as it were. I might also have another stab at doing it myself. I'll let you know how I get on.

    Thanks again. :)

  9. Hi all,

    I find it very much easier when processing my images, to have all my files sorted into files by temperature.

    However, I've decided I find it tedious! And it's such a mechanistic process, I'm sure it could be automated using a .BAT file.

    It would do this:

    1. Start in the current folder

    2. Set a counter to 1

    3. Look for files with '1C 'in the name

    4. If there's at least one file, make a folder called 1C and move them all to it, if not then do nothing

    4. Increment the counter and repeat, to look for 2C, 3C etc until, say, 30C (yes, I do have some files at that temperature believe it or not - non-cooled DSLR during height of summer) 

    So instead of having to do this all myself, I could just run, say, sort.bat and it would do it all for me.

    I think it's probably fairly simple if you know what you're doing. I've dabbled in code in the past and have looked around for examples, but can't really find anything I could adapt without spending frustrating hours/days/weeks/months/years/decades/centuries/millennia/epochs/aeons getting it wrong.

    So, does anyone have anything like this already, or any DOS gurus willing to have a go?

    Thanks, Brendan



  10. So, another year of astrophotography. Started off well, ended up very cloudy indeed. Here's a quick retrospective, nothing fancy, just throwing it all into MS Photos and adding some music. Hope it's OK to share here. All photos and music © me (yes, there is music, it just starts very quietly - better played on anything other than laptop or mobile speakers).

    • Like 6
  11. My last point was really referring to how I'd expect APP to have yielded better results generally, rather than just giving me better results with Ha. I wasn't really referring to colour management.

    I was just surprised that APP, despite taking much, much, much longer to produce a result, and being a pay-for product, didn't produce results that were much different from DSS in any respect that I could see. I know the maths is essentially the same. It just surprised me, is all, and I was looking for any recommendations that might help me get a better result.

  12. Hi all,

    I'm trialling APP for the second time, as a stacker before processing in StarTools. First time around I didn't know what I was doing, this time a year later I think I'm more clued up - but I'm still not quite getting the results I'd expect when compared to the free Deep Sky Stacker, and I'm wondering whether I'm doing something wrong here.

    I've been testing them against each other, trying to process them as closely as possible in StarTools, and honestly I'm not seeing much of a difference. My hardware is a modded EOS1000D, Sky-Watcher 130PDS on an NEQ6. I'm capturing using APT, then stacking in DSS using the Auto Adaptive mode, and in APP using the recommendations at https://www.startools.org/links--tutorials/starting-with-a-good-dataset/recommended-app-settings, then taking the linear output and post-processing in StarTools, without adding denoise just so I can really see what's going on. I use 25 flats, 25 dark flats and 50 flats each time.

    Here are some examples:






    Now, I'm probably still going to invest in APP because I've just started doing some Ha work and it beats DSS hands-down for that. But, I would kind of like APP to do much better at RGB work than DSS too, especially given the price, and given the amount of time it takes to process.

    Is there anything I might be doing that is really badly wrong here, or some button or switch or tick box I should be looking at? Or is this really just a reflection of the limitation of my gear/technique?

    Thanks, Brendan

  13. And my second Ha image! The Pacman nebula.

    * 8:45 hours of H-Alpha from 105x300s subs
    * 2:49 hours of RGB at ISO800 from top 90% of 47x240s subs
    * Bortle 4, Moon 58% phase, 61° height
    * 25 flats, 25 dark flats, 50 darks
    * Sky-Watcher 130PDS with primary baffle, NEQ6 with Rowan belt, EOS1000D minus IR filter, 7nm H-Alpha filter, 0.9x coma corrector, APT, PHD2, APP, StarTools, Photoshop, Topaz DeNoise AI


    • Like 6
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