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Thread: Guide to the maximum exposure time to avoid star trails

  1. #1

    Default Guide to the maximum exposure time to avoid star trails

    Hi,
    Seem like quite a number of people like to "shoot stars". Below are a guide to the maximum exposure time allowed in order to avoid star trails when using a tripod. To get perfectly sharp stars, use only 1/3 of the maximum exposure time.

    When aiming at celestial equator (Declination 0 degree)... basically overhead in Singapore.
    Lens Focal Length: Maximum exposure Time
    18mm: 55s
    24mm: 40s
    28mm: 35s
    35mm: 30s
    50mm: 20s
    100mm: 10s
    135mm: 7.5s
    200mm: 5.0s
    300mm: 3.3s
    400mm: 2.5s

    When aiming at Declination +/- 30 degree... around 60 degree above north/south horizon in Singapore.
    Lens Focal Length: Maximum exposure Time
    18mm: 65s
    24mm: 50s
    28mm: 40s
    35mm: 33s
    50mm: 23s
    100mm: 12s
    135mm: 8.5s
    200mm: 5.5s
    300mm: 3.8s
    400mm: 3.0s

    When aiming at Declination +/- 45 degree... around 45 degree above north/south horizon in Singapore.
    Lens Focal Length: Maximum exposure Time
    18mm: 80s
    24mm: 60s
    28mm: 50s
    35mm: 40s
    50mm: 28s
    100mm: 14s
    135mm: 11s
    200mm: 7s
    300mm: 4.7s
    400mm: 3.5s

    When aiming at Declination +/- 60 degree... around 30 degree above north/south horizon in Singapore.
    Lens Focal Length: Maximum exposure Time
    18mm: 110s
    24mm: 85s
    28mm: 75s
    35mm: 60s
    50mm: 40s
    100mm: 20s
    135mm: 15s
    200mm: 10s
    300mm: 6.5s
    400mm: 5.0s

    When aiming at Declination +/- 75 degree... around 15 degree above north/south horizon in Singapore.
    Lens Focal Length: Maximum exposure Time
    18mm: 220s
    24mm: 160s
    28mm: 140s
    35mm: 110s
    50mm: 75s
    100mm: 40s
    135mm: 30s
    200mm: 20s
    300mm: 13s
    400mm: 10s

    Enjoy "stars shooting" and have a nice day.

  2. #2
    Moderator Francis247's Avatar
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    Default Re: Guide to the maximum exposure time to avoid star trails

    Hi Weixing,

    This is very good and informative. Thanks for sharing.
    I will make this as a Sticky Thread.
    Thank you very much.
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  3. #3
    Member/Tangshooter Redsun's Avatar
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    Default Re: Guide to the maximum exposure time to avoid star trails

    very good info
    but but
    for a 1st timer im not really sure what Declination is referring to?

  4. #4
    Senior Member
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    Default Re: Guide to the maximum exposure time to avoid star trails

    Quote Originally Posted by Redsun View Post
    very good info
    but but
    for a 1st timer im not really sure what Declination is referring to?
    vertically above you is 0 degree, declination = angle from the direct vertical above you
    chezburgr i can haz?

  5. #5

    Default Re: Guide to the maximum exposure time to avoid star trails

    Hi,
    Quote Originally Posted by Redsun View Post
    very good info
    but but
    for a 1st timer im not really sure what Declination is referring to?
    In Astronomy, the coordinate system use to specify the locations of stars and astronomical object on the sky is call Equatorial Coordinates System. The Equator of the sky is called Celestial Equator, which is projected from Earth's Equator to the sky. The Earth's North and South poles is projected on the sky as North Celestial Pole and South Celestial Pole.

    Equatorial Coordinates use two values to specify the location of an astronomical object on the sky called Declination (Dec) and Right Ascension (RA). Declination is like latitude on Earth and Right Ascension is like longitude on Earth.

    Declination from Celestial Equator (0 degree) to North Celestial Pole (+90 degree) is positive value and from Celestial Equator (0 degree) to South Celestial Pole (-90 degree) is negative value.

    By the way, the Declination on the sky directly above you is basically same as your latitude. Our latitude in Singapore is 1 degree N, so the Declination directly above us is +1 degree.

    Hope the above helps.

    Have a nice day.

  6. #6

    Default Re: Guide to the maximum exposure time to avoid star trails

    wow! im impressed. this must be a hell load of research!

    sure useful!

  7. #7
    Member fmeeran's Avatar
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    Default Re: Guide to the maximum exposure time to avoid star trails

    Awesome! Have been trying to locate the reverse. How to get star trails. This info helps.
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