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Helix_PS_09b

NGC7293 – Helix nebula

Ha – Red channel
10x5min + 7x10min

SII – Green channel
1x5min + 7x10min + 3x15min + 17x20min

OIII – Blue channel
10x5min + 8x10min

Taken from Rushcutters Bay in Sydney with my Atik 314L+, SW 120/f5, EQ6

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9 Comments

  1. Great picture as always!
    Another question: Up to date, I have just taken two little astropictures (M31 and M42) with nothing else but my tripod and, a 200mm tele and a 2.5 second exposure time.
    In both cases, I stacked about 50 images in Deep Sky Stacker. Both times, the resulted stack was really bright and in a yellowish town, without much detail in colour. I wanted to ask you whether you had a clue if this was due to the short exposure of each individual shot (that did not get lots of colour infos), or if it was due to light pollution? In the case of M42, I got a little bit of colour out of the image, but just after heavily processing it in lightroom. Are your stacked picture also that bright? Or am I doing something wrong?
    Have a great week, looking forward seeing more astropictures!
    Charlie

    • hughca
    • Posted July 23, 2013 at 1:42 pm
    • Permalink

    Thanks!

    My DSLR images out of DSS are usually quite dark and I have to push them quite a lot in Lightroom. Not too sure why you’re not getting much colour info out of your images but it would depend on your camera and how it goes at high ISO. In general higher ISO reduces the dynamic range that the camera is capturing so the images look flatter than they would when doing longer exposures of lower ISO. What sort of camera are you using? and what ISO are you imaging at?

    Also DSS has different options that affect the colour balance. I don’t know too much about them but I use the “Use per channel background calibration” option and it seems to work for me.

    In this old post of mine I did a few images in a similar way to you: https://hughsblog.wordpress.com/2012/08/08/after-dark-ii/
    Also a friend of mine had a go at M42 using his Canon 7D and a 200mm, perhaps compare the amount of colour in his: http://www.flickr.com/photos/chrisharrispix/9096607555/

    I would love to image M31 but it never rises very high above the horizon for me in Sydney.

  2. Thank you very much!
    I shoot with my Canon 60D @ about ISO 3200. The M42 came out really great, but I got next to no colour details with my M31 picture:
    _M31_V4-3
    Ok, I get that there might not be much colour information when you have massive light pollution and a really short exposure time. But still, I would not have thought that I would be unable to get any kind of info :D
    M31 was actually my first “astropic” that I ever took. And I was asking myself what I might have done wrong :D
    I am now saving for an EQ3 mount and a 500mm refractor, on which I can install my camera. So hopefully, I’ll be able to achieve longer exposures!
    Btw, love the other pictures you linked!
    Charlie

    • hughca
    • Posted July 23, 2013 at 2:48 pm
    • Permalink

    Hey Charlie, I think your M31 pic is pretty good considering it was just short exposures. I don’t have any experience imaging (or even viewing!) M31 but I think the colour is mainly in the outer fainter bits. You could try and take heaps more short images thereby improving your signal to noise ratio and allowing you to push the image further in Lightroom. Also perhaps take some at ISO6400 to get a bit more info, just be sure to take heaps and also take heaps of dark frames at both ISO3200 and 6400. I think if you took 100 images at 3200 and 100 at 6400 plus 100 darks frames at 3200 and 100 more at 6400 then chuck that all into DSS you should get something pretty good!

    Actually just thinking about it now, are you taking dark frames? if not that might explain why your images are bright out of DSS?
    (In case you’re wondering what dark frames are, they’re basically images you take at the same ISO and exposure time but with the lens cap on. When you give these to DSS it uses them to eliminate the sensor/ISO noise. Also make sure you take them shortly after you take your light images as the temperature of the sensor changes the noise and you want them to match)

    When it comes to getting a scope and a mount it can be a hard decision. When I was where you are I was initially thinking about an EQ3 but eventually decided on an EQ5 as the EQ3 is generally not regarded as suitable for astrophotography unless you’re doing fairly short exposures (max 30 seconds) at fairly short focal lengths, like 200-300mm.
    With my EQ5 I was getting around 60 second exposures with my ED80 (600mm) and when I eventually invested in a guide scope/camera it did allow me 5-10 minute exposures but gave me a fair bit of stress in the process.
    The general rule/advice when getting into astrophotography is to spend the majority of your budget on the mount and as such most recommend the HEQ5 as the minimum mount to get good results with little stress. I’ve just bought an NEQ6 and the difference between it and the EQ5 is huge.
    You can see that this gets very expensive very quickly but there is an alternative. If you’re not ready, or can’t, commit a decent amount of money then I would recommend either a Vixen Polarie or an iOptron SkyTracker. These attach to a normal camera tripod and allow you to mount a DSLR and track the stars. The results I’ve seen from these look great but you wouldn’t want to be using anything longer than about 200mm. Do a Google image search for either of these and you’ll see the sort of stuff people are getting with them.
    Also check out one of the astronomy forums, I’m on one called IceInSpace.com.au which is mainly for the southern hemisphere but everyone’s welcome. There are plenty of posts on there from people in a similar situation plus it’s good to see what others are doing with the equipment you’re looking at.

    BTW I love your street photography, really nice stuff :-D

  3. Thank you very much for your reply!
    The thought to take more than 50 images never occured to me. Do you really think that I’ll get more details out of M31? With only 2.5 seconds, I won’t really get too much details.
    But I’ll try your tip with different ISO settings. DSS will accept and stack images with different ISO settings (never tried that).
    Thank you also for the part with the mount! The decision is really hard as there are many things to choose from. I’ll google your recommendation!
    With a bit of luck, I’ll get out of the city again in a few days. I’ll try the exposure with different ISO settings!
    Thank you so much :D

    • hughca
    • Posted July 23, 2013 at 3:35 pm
    • Permalink

    It’s definitely worth a try with more images of M31. I think, especially at high ISO, you can’t really have too many images! You could even try a bunch at ISO12800 and throw them in too, just make sure you do plenty of dark frames as well.
    Good luck :-)

  4. Thanks :D
    Just to get it right: I will stack all the pictures at ISO 3200 and get one TIFF image.
    I will stack all pictures at ISO 6400 and get one TIFF image.
    Will I then stack those two (or more with other ISO settings) together? Or can I only do one stack with all 300 pictures at different ISO settings?

    • hughca
    • Posted July 23, 2013 at 3:42 pm
    • Permalink

    I would load all 300 into DSS at the same time as well as all 300 dark frames. DSS knows what ISO the images are taken at and only uses dark frames of the correct ISO with the correct light frames, but it will stack all of them to produce a single image with more range than any of them separately.

  5. okay, will try it. But it is going to kill my computer :D
    Cheers,
    Charlie


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