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Help Needed: Canon 200D / Irix Firefly 15mm F/2.4 - elongated stars

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    Help Needed: Canon 200D / Irix Firefly 15mm F/2.4 - elongated stars

    I'm really hoping someone can help with this one.

    A little bit of background: Initially, I thought the issue was build quality of Samyang 14mm lens. However, I've now purchased a better lens and been to a dark sky site and taken some Milky Way images.

    Equipment: Canon 200d, Irix Firefly 15mm F/2.4 lens, tripod, shutter release cable.
    Settings tried: ISO 800-3200, shutter 20-25secs, aperture F/2.4-and various stops down.


    Image 1: = F/2.5, 20.3sec, ISO3200
    KnTGxHJh.jpg




    Issue: Stars are dashes (even in centre of image). This was the same issue with the Samyang (previously). I'm now struggling with why the Irix is producing the same results. Could it be the Canon 200d has a problem?


    Note: I've also tried OFF/ON settings for each of the following (in different combinations):
    • Lens Aberration
    • High ISO NR
    • Mirror Lock
    Results do not change.

    Image2: = shortest length exposure taken: F/2.5, 12.5sec, ISO6400
    NNnLiarh.jpg



    It's a little better - but still has some coma when zoomed.

    Much of what I've read suggests 30secs untracked for Milky way shots - but that's clearly not possible here - due to whatever I am doing wrong. So, how with <15secs do I capture enough to be able to get decent Milky Way detail?

    Does anyone, have any ideas that may help me resolve this?

    thanks
    Last edited by brenski; 09-09-2021, 13:13.

    #2
    Hmm Brenski,

    I hesitate to give advice because there are some brighter stars than me on the Astro. front and also I don't know how much this is new to you . So forgive me if some of this you already know but I'll forge ahead having done 7 nights in Tromso to photograph the northern lights & milky way

    1. I used the Samyang 14mm. Don't belittle this little baby but if you have the full manual version, as I did, you MUST calibrate the infinity point on it first (You Tube has guidance on this) Mark it on masking tape on the barrel so you know exactly where it is
    2.Use a SOLID tripod, hang weights from it to keep it absolutely rigid when in use
    3. Use a cable release or remote to start shooting, don't touch your equipment
    4. Use the widest aperture you have, always.
    5. Stars will move and the 500 rule is generally thought to be good. This states that the maxm time in seconds before movement shows is 500 divided by your focal length x crop factor 1.6
    So for the samyang that's 500 divided by (1.6 x 14) = 22 secs
    6. My guide suggested ISO of 2500 or 3200 and I stuck with that.
    7. My understanding is that high ISO noise reduction is only used when shooting jpegs and adds to the picture a further time to merge 2 parallel images. So no use if shooting jpegs. I would recommend shooting RAW anyway so you can fiddle a bit in PP
    8. I would always do any lens aberration correction in PP not in camera
    9. Mirror lock ( a tiny tiny vibration at the start of the image ) is not considered to impact on the finished image, so no worries here either way
    10. See if these suggestions or those that may follow improve your images before looking at a more expensive camera or lens. Bear in mind that if you do get the bug then inevitably you may consider than an entry level crop camera will have some limitations, even though it’s a very well thought-of solid performer
    Last edited by lunarbo; 09-09-2021, 16:30.
    Canon EOS R6, Canon 5d mk iv plus the usual suspects ......

    https://www.flickr.com/photos/bo_fo_to

    Comment


      #3
      lunarbo thanks for your advice. some useful stuff there. however, i think the Irix lens i'm using is pretty-much spot on for focus.
      In live view, i've zoomed right in and then used a Jeweller's Loupe to ensure the stars look nice and round/tight and (more importantly) as small as possible.

      I'm thinking that this will mainly down to exposure time, but can't understand why so many articles and guides claim that quality untracked (sing;e-shot) Milky Way images can be had @ 25secs. on my 200d/15mm Irix, the stars are elongated at 22 secs and show coma @ 14 secs.

      Comment


        #4
        I’m not as sure as you are that infinity is correct and would suggest that you test this in day time and see the results on your screen,Then make sure this is fixed before setting out at night. The Irix was new to me but I read that it is again manual focus and also that there is some variance in quality.
        Personally I just don’t want to be fiddling around in the dark adjusting anything
        Then if your basics of tripod and remote are correct it’s on to settings, as I suggested above
        You seem to be very concerned with what others are getting at 25 secs, you may well achieve reasonable results at 15 secs with your equipment. Longer may not be better if the ISO is correct
        Finally if you have exhausted all possibilities, and don’t be too quick on this, you may have to consider if your camera has a good enough sensor to record something 100000000000 etc miles away at the accuracy you expect or hope for!

        Canon EOS R6, Canon 5d mk iv plus the usual suspects ......

        https://www.flickr.com/photos/bo_fo_to

        Comment


          #5
          Hi lunarbo - thanks for your patience, I suppose i have to balance my expectations here.
          I suppose that - from what you are saying - that the elongation could also be down to infinity focus, but it also may not be (could just be lens build quality), or it could be camera.

          So, to eliminate the lens first, what kind of distance would you suggest as a reasonable daytime "infinity" setting for the Irix 15mm? and if, it is in focus, what would a a decent daytime result be?

          thanks

          Martin

          Comment


            #6
            Yes, nailing infinity is key and can vary by as much as a centimetre on your dial, despite wherever the sign is marked as infinity.

            I would suspect this is the culprit more than blaming the equipment

            You will find lots of videos on You Tube, but you basically look for a very distant sharp static object with good contrast & details ( eg X lines on TV aerial, weathervane)
            With tripod etc set up solid focus manually on that object, blow up the image on the back of the screen and when you think it’s the clearest fix that point with masking tape across the dial to stop any further movement and mark with a thin pen across the tape .
            I would then check it on your PC back home , blowing up the image as much as possible
            If you’re not totally happy or just want to double check, remove the tape from the camera side and make 2 thin lines on the lens tape just before and just after your previous line. Call these 1 to 5
            Go back to your test site and take further pictures with the lens in each position 1, 2, 3, 4 ,5 as described above. If you put one or more of your fingers into the shot you will not be mistaken when you get home !

            Check on PC back home, make your selection from 1 to 5, re-tape and re-check back on your test site in daytime

            All this preparation does mean that when you get to the night sky then you know your infinity is as good as you can get it .

            Your tripod as I said must be rock solid, extension of the vertical pole on your tripod should be at a minimum, no wafting around.Check also the screw connection of camera to plate and tripod head - tight to avoid slow droop

            Then I would try test shots at 10, 15, 20 secs both at 2500 and 3200 ISO, and maybe 6400 although this will be noisier.

            Find out what's best for your camera and your lens combo, this is all that matters

            Canon EOS R6, Canon 5d mk iv plus the usual suspects ......

            https://www.flickr.com/photos/bo_fo_to

            Comment


              #7
              that's really brilliant advice, will get on it this afternoon. thanks loads

              Comment

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