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Focal Length vs. shutter speed

Discussion in 'Lens Lust' started by danmab, Jul 20, 2007.

  1. danmab


    Apr 26, 2007
    I've been trying to wrap my head around this, and I think it's fairly obvious but I can't pinpoint why.

    We all know the general "rule" of setting your shutter speed to the equivelant of your focal length (i.e. a 200mm lens should be at least set to 1/200sec) to essentially freeze action.

    So let's say you have an 85mm & a 300mm. Given a moving object that stays constant from the lens, I would assume the 85mm set at 1/300 freezes the action better than the 300mm set to 1/300.

    If we say the 300mm is 353% "larger" than the 85mm, does that mean the 300mm should be set to at least 1/1000 to have the same frozen action?

    Sorry if this is confusing' that's probably why I can't seem to logically piece it out.
  2. It's not freezing action per se, that your shutter speed factor is to consider. Depending on what you are shooting, 1/300 may not be fast enough to shoot fast moving objects like Cars or boats. It may not even be fast enough to "stop" the action of some people sports (but it should).

    The 1/shutter speed is to reduce the risk of blur from unsteady hands. The longer the focal length the more apt for vibration to show up in the image.

    That's why VR is making a push. It helps people get useable and perhaps quality images from a 300mm lens at shutters speeds less than 1/300th of a seconds hand held.

    Certainly the faster the shutter speed, the better the opportunity to catch both fast moving action and reduce (perhaps eliminate) vibration from the shooter.

    Hope this helps.
  3. TimK


    Apr 17, 2006
    Hong Kong, China
    Because of the magnification, longer lens will exaggerate vibration caused by unstable hands/tripods. etc. Hence faster shutter speed will be needed.
  4. What action are you talking about? Lens vibration action or the action of what you are trying to photograph?

    The 1/mm is a general rule for being able to hand hold at a given shutter speed. I could be wrong (and often am) but I don't recall a rule like you describe for freezing action of the subject.
  5. cotdt


    Jul 14, 2007
    Bay Area, USA
    Last edited by a moderator: Mar 15, 2017
  6. mood


    Jun 27, 2007
    So Fla
    I think it depends on the size of the lens
    my 80-200 for sharp shots needs to be 400 and up
    fortunately with 2.8, its not too hard for what i shoot, otherwise i use a tripod

    my 35 f2 , obviously is sharp at much lower ss

    I agree also this has nothing to do with freezing action, just blur from shake
  7. I wouldn't worry about this rule (really more of a guideline) as far as "freezing action" goes. TimK is right in that the increased magnification means you're viewing a smaller area through a longer lens, so you'll notice shake that much easier. I could photograph something moving really quickly (right in front of me) with a 12 mm focal length, and 1/12 of a second isn't going to freeze it in the frame - I'm going to see blur.
  8. I don't mean to say you have to shoot at 1/mm to get a clear shot. It's just a general rule of thumb.
    Last edited by a moderator: Mar 15, 2017
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