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x6gas last won the day on July 13 2013

x6gas had the most liked content!

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About x6gas

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  1. Lovely image, as ever.
  2. Cracking shot... I too am getting a bit of a magenta tinge in the background but it's still a stunning capture and process.
  3. Agree with @vlaiv - congrats for even giving this a go and thanks for an interesting, informative, and well-constructed post. I'd be delighted to have emulated the Hubble image as well as you have!
  4. Love it. amazing with a DSLR...
  5. Beautiful galaxies and you've processed them to give a very natural feel. Lovely stuff.
  6. Yes it does make sense to stack with lights and bias frames. So long as you are not using flats (or darks) then I don't believe it matters whether you tell the stacking software that they are bias or darks since both are subtracted from the light frames. Scrub that last bit. I think you probably do want to tell the stacking software they are darks rather than bias frames - reason being the bias frames may only be subtracted from the flats since the software should expect the darks to correct the read noise as well as thermal noise. If the software is smart enough to know that in the absence of darks, it needs to subtract bias from the lights then that's fine, but probably safer just to tell the software to treat them as darks then you can be sure that they'll be subtracted from the lights... I have, by the way, seen workflows telling you to correct the dark frames with bias frames which seems odd because then you need to correct the lights with darks and bias (because you've taken the bias out of the darks, if you follow) - so you are adding two steps you don't need. If there is an advantage to this then I'd be grateful if someone could explain!
  7. When you say "dark-bias" do you mean bias corrected darks or darks and bias frames? My understanding is that, as the bias signal is present in the dark frames as well, you just need to subtract the dark from the light frame as this contains both the read noise and the thermal noise. There is no point in using bias corrected darks if you are not using flats. To put it another way, if you are using darks but not flats then you don't need bias frames at all...
  8. Bias frames and Dark frames are both subtracted from lights as part of the calibration process - the former to subtract read noise and the latter thermal noise. If you don't have much thermal noise (because the exposure is short or the camera cooled) then you can just subtract Bias frames. Can't remember if DSS allows you to add Bias frames. If it does then add them to DSS as Bias (I suspect it will also then subtract the Bias from the Flat frames) and don't put anything in as Darks, if not then just put them in as Darks and DSS will sort it out. HTH, Ian
  9. x6gas

    M51 .

    Brian - you've got some great detail here but I think there are a couple of things you could try to make it even better... There is a bit of a gradient - have you tried GradientXTerminator? Pretty sure that will see it off... As Ole says the colour balance seems a bit off - the galaxy looks very blue. I appreciate that you are using a OSC camera but you can drop the blue a bit or raise the greens and reds... You've got great kit and what looks like excellent data - well done on that - and you're a couple of tweaks away from having a terrific image.
  10. Same here - mine are also often wildly different. Can't recall who, but someone suggested changing the colourspace to sRGB before saving....
  11. Very nice Gav. As you say, different again - and I like yours too. You've stretched it harder than I did and as you say the balance between the blue and red stars is very different...
  12. Well your tutorials are very thorough, Barry, and are incredibly helpful - nice to have text tutorials too as I can follow along without annoying the wife too much! I can guess how long it takes you to put these together so very many thanks and I look forward to future ones. I installed PI with some trepidation but thanks to the tutorials it has been a genuinely interesting and enjoyable learning experience.
  13. Thanks for the reply Gav. Personally I don't think there is a "best way" - just different and I can process data using my 'standard' workflow and then process it again making a minor change and the result can be really different! Yes I wasn't sure what to make of the very red stars - especially the one to the right of the image. I decided to leave it as it came out of PI in the interests of the comparison. Interestingly they are there, very red, in the unstretched data but don't come out so strongly when I stretch the data in PS. Very happy to share the data - I'll PM you.
  14. For the past couple of weeks I've been using the trial version of PI to see if I can get on with it; coming back to the hobby after a few years PI seems much more established and the results being posted on here look good so I thought I'd give it a go. I was pleased to find that - for me - it wasn't too daunting to get to grips with, especially with the excellent tutorials posted by SGL members Harry Page and Barry Wilson (thanks guys!). Now there is clearly a lot to learn as there are a lot of user defined parameters but I think that's inevitable with a flexible and capable piece of software. After much fettling (and this did take me a long time to get to grips with) I've found the calibration and stacking to work really well and, while I am still exploring, I find the PhotometricColorCalibration process to be really useful. Anyway, I've been playing with M35 RGB data to keep things nice and simple and I thought some members, perhaps those considering trying out PI, might be interested in the comparisons below. The data is 300s subs of R x 20, G x 21, and B x 19 so 5 hours with bias, flats and darks. Here's my original using my old workflow (registered using Registar, stacked in AstroArt 5, colour combination, stretching, and other processing in PS). And here is a version which was calibrated, stacked, combined and colour corrected in PI, but stretched and with star colours boosted in PS, with a small Gaussian blur applied. And finally this is version done entirely in PI, stretched with just one application of the arcsinh stretch function and smoothed with a blur using the convolution routine. I think I like the star colour in the PI processed image - it is certainly seems easier to get strong star colour without introducing a lot of noise. I have to say that, once you know your way around, PI seems much quicker to use and it appears that - on this simple RGB image at least - I can do everything in one programme and get a result I really like. This is enough for me to decide that I will be purchasing a full licence of PI and I must confess that I am quite looking forward to finding out what more it can do. Hope this is helpful. Clear skies, Ian
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