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Thread: A photo for star trails

  1. #1

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    A photo for star trails

    Dear all,

    I have considered to take some star trail photos for a while. Now from Sunday to Tuesday, we had clear sky each night, and I tried 3 nights.

    The first two nights were not successful. The following one was from last night. I worked out the suitable combination of Aperture and ISO seemed to be f/5.6, ISO 200, this would give me about 4 minutes exposure, while there were quite a lot of artificial lights around.

    A photo for star trails

  2. #2
    Rodders's Avatar
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    Re: A photo for star trails

    Nice job Yan,
    The stars and the tree are well focused. I see you were pointed almost perfectly North, which is where you get the fastest star trail effect.
    You could also try lowering the iso to 100 (or less if you can) and run the exposure out to around 10 min or more.
    Those artifical lights can be a pain

  3. #3
    Moderator Dave Humphries's Avatar
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    Re: A photo for star trails

    Hi Yan,

    Nice composition, good choice of location - and nice star trails of course!
    It would make a decent desktop background picture at a higher resolution.

    The biggest problem I see above is, to an extent, beyond your immediate control; the down sizing to 800 pixels width has left 'steps' in the curving trails, most noticeable on the right side.

    I would guess (correct me if I'm wrong) this is because you uploaded at a higher resolution and posted the image link here from your image hosting service's automatically created 'other size' photos?
    For critical images like this where you really need it to display in high quality here, the only way around this is to down size yourself to the size you intend to post here, check and use a different method to avoid 'the jaggies', upload the now 800 or 1000 width image directly, then put the link here to the 'original' size where it is hosted. Just be sure to remember to always keep a processed copy at the full resolution image too, I always Save As and rename my downsized pics with a "_W1024" suffix.

    One more thing, for best results; do the final USM sharpen after the down sizing (and before Save As).

    Of course, if I guessed wrong, that was a waste of everyone's time

    Cheers,

  4. #4

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    Re: A photo for star trails

    Quote Originally Posted by Rodders View Post
    Nice job Yan,
    The stars and the tree are well focused. I see you were pointed almost perfectly North, which is where you get the fastest star trail effect.
    You could also try lowering the iso to 100 (or less if you can) and run the exposure out to around 10 min or more.
    Those artifical lights can be a pain
    Rodders,

    Thanks for your comment. You are right, the direction is facing north - I have been observing this tree for 2 years for all seasons and all different times.

    I indeed tried to run 10 min, the effect seemed not as nice as 4 minutes, because the star trails were twice longer and very dense.

  5. #5

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    Re: A photo for star trails

    Quote Originally Posted by Dave Humphries View Post
    Hi Yan,

    Nice composition, good choice of location - and nice star trails of course!
    It would make a decent desktop background picture at a higher resolution.

    The biggest problem I see above is, to an extent, beyond your immediate control; the down sizing to 800 pixels width has left 'steps' in the curving trails, most noticeable on the right side.

    I would guess (correct me if I'm wrong) this is because you uploaded at a higher resolution and posted the image link here from your image hosting service's automatically created 'other size' photos?
    For critical images like this where you really need it to display in high quality here, the only way around this is to down size yourself to the size you intend to post here, check and use a different method to avoid 'the jaggies', upload the now 800 or 1000 width image directly, then put the link here to the 'original' size where it is hosted. Just be sure to remember to always keep a processed copy at the full resolution image too, I always Save As and rename my downsized pics with a "_W1024" suffix.

    One more thing, for best results; do the final USM sharpen after the down sizing (and before Save As).

    Of course, if I guessed wrong, that was a waste of everyone's time

    Cheers,
    Dave,

    Thanks for your comment. Your guess is right. I uploaded full size, but picasaweb automatically reduced to a very small size, and I used that link.

    Now I downsized the image following your instruction (did USM after downsize and before Save As), and attach here. Hope this gives a better effect.

    img_6176-small.jpg
    Attached Images Attached Images
    Last edited by Dave Humphries; 22nd July 2009 at 10:35 AM.

  6. #6
    Moderator Dave Humphries's Avatar
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    Re: A photo for star trails

    Hi Yan,

    I think it is better, but not as gone as I would have hoped; which down sizing method did you use; bicubic or bicubic sharper?

    Do you see it?
    In particular, I see two faint horizontal lines across the brightest, right hand most trail, even when I click the bar to view at full width (now I have posted it inline).

    Thanks,

  7. #7

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    Re: A photo for star trails

    Quote Originally Posted by Dave Humphries View Post
    Hi Yan,

    I think it is better, but not as gone as I would have hoped; which down sizing method did you use; bicubic or bicubic sharper?

    Do you see it?
    In particular, I see two faint horizontal lines across the brightest, right hand most trail, even when I click the bar to view at full width (now I have posted it inline).

    Thanks,
    Dear Dave,

    I used bicubic down size method. I don't what is the difference between this and bicubic sharper.

    I cannot see the two horizontal lines there. Maybe they are clouds? I am not sure.

  8. #8
    Moderator Dave Humphries's Avatar
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    Re: A photo for star trails

    Quote Originally Posted by Yan Zhang View Post
    I cannot see the two horizontal lines there. Maybe they are clouds? I am not sure.
    No, not clouds for sure. I see 2 horizontal dark lines through the trail, one just before mid-way and one near the end.

    I am looking on a different monitor now and while the first exhbits the problem whether enlarged to 800 pixels or not, the second doesn't really show it when enlarged to 1024 pixels, but I think this is just because it's running at a different native resolution.

    One way to prove if it is in the picture or n my LCD would be a screen grab, I'll ahve a go tonight and post the result - or scrape the egg off my face

    Cheers,

  9. #9

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    Re: A photo for star trails

    Dave,

    Thanks for spending time on my image.

  10. #10

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    Re: A photo for star trails

    Nice photo I would love to be able to take photos like that. The guy who is trying to tell me how to do stuff like that says I need a nd filter. He's told me to get a Helipan 3.0? So you can get long exposures. How would I work out the settings in manual if i wont to take one over 30 mins. Ive read somewhere you can take them over hours. Not very clued up on all this but want to learn.

  11. #11

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    Re: A photo for star trails

    Quote Originally Posted by bucketman View Post
    Nice photo I would love to be able to take photos like that. The guy who is trying to tell me how to do stuff like that says I need a nd filter. He's told me to get a Helipan 3.0? So you can get long exposures. How would I work out the settings in manual if i wont to take one over 30 mins. Ive read somewhere you can take them over hours. Not very clued up on all this but want to learn.
    Thanks for your interest. For star trails like this, you don't need too long exposure time, this one is about 4 minutes, no filter will be needed.

    However, if you want a complete milky way-look star trails, you do need over 2 hours exposure.
    But with DSLR, such long exposure couldn't be feasible, as so many noises will be introduced on the sensor - I didn't try, but read from some people's comments on this issue. The way to get around of this, is to use multiple exposures, each with 4-5 minutes, with minimal interval in between, then take about 20-25 shots, then blend in PS. I did try to take 4 intervals and blend in PS, then effect was good.

  12. #12

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    Re: A photo for star trails

    Quote Originally Posted by bucketman View Post
    The guy who is trying to tell me how to do stuff like that says I need a nd filter. He's told me to get a Helipan 3.0? So you can get long exposures. How would I work out the settings in manual if i wont to take one over 30 mins. Ive read somewhere you can take them over hours. Not very clued up on all this but want to learn.
    You shouldn't need an ND filter - just stopping down the lens should be sufficient (keeping in mind that your not really letting in more light with a longer exposure, it's more a case of letting in the same amount of light, but in different areas).

    Best idea is just to experiment - as Yan says, multiple short exposures will give a much better result.

  13. #13
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    Re: A photo for star trails

    Quote Originally Posted by Dave Humphries View Post

    One more thing, for best results; do the final USM sharpen after the down sizing (and before Save As).

    Of course, if I guessed wrong, that was a waste of everyone's time

    Cheers,
    Not a waste of time, but extremely helpful!

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