Canon 7D iris problems

Discussion in 'Beyond the Basics' started by jpenna, Nov 7, 2009.

  1. jpenna

    jpenna TPF Noob!

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    I explain it here:


    Anyone know what's up?
     
    Last edited by a moderator: Sep 11, 2014
  2. Josh66

    Josh66 Been spending a lot of time on here!

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    That's normal.

    ...I don't know how good I'm going to be able to explain it though. I can 'see' it, but I'm not really sure how to say it, if you know what I mean.

    Wide open, it's stopped down more at the long end - but really the aperture is the same size. The f/# is only different because the focal length is longer.

    At the tele end, it's maintaining a constant f/# - but the only way to do that is to change the actual size of the aperture.

    f/8 @ 50mm will not have the same size opening as f/8 @ 135mm.

    EDIT
    For the same reason, it can probably stop down more at the long end. f/32 (or maybe f/22) is probably the smallest it goes at 18mm, but at 135mm it probably can go down to f/45. Not sure about that lens specifically, but some are like that.
     
    Last edited: Nov 8, 2009
  3. RyanLilly

    RyanLilly No longer a newbie, moving up!

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    I figure in real world applications you never going to rack the zoom back and forth like an idiot anyway.
     
  4. Derrel

    Derrel Mr. Rain Cloud

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    Not very well-said, but I think you're right on the money. And Ryan's observation is quite eloquent as well.
     
  5. Enough Already

    Enough Already TPF Noob!

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    So you would not use the zoom in any fashion if you were using video mode??
     
  6. Stosh

    Stosh TPF Noob!

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    Josh is right on - doesn't sound like a problem at all.
    First thing most people need is a better understanding of aperture and f-ratio. Aperture is a physical size determined by the iris. F-ratio is the ratio of focal length divided by aperture. So when people say my aperture is f/2.0 or whatever, that's technically wrong. Your f-ratio (or f-number) is 2.0, your aperture is half your focal length (so for a 50mm lens at f/2 your aperture is 25mm).

    That being said, when you zoom, you change focal length. To maintain a constant aperture, the f-ratio must change. To maintain a constant f-ratio, the aperture must change. This is why you hear the iris changing size - it has to if you want it to maintain a constant f-ratio. Sounds like it's working exactly like it should.
     
  7. inTempus

    inTempus TPF Noob!

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    You can always start here.
     
  8. KmH

    KmH Helping photographers learn to fish Supporting Member

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    linky, no worky.
     
  9. ErectedGryphon

    ErectedGryphon TPF Noob!

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    Linky worky, your computy no worky:mrgreen:
     
  10. inTempus

    inTempus TPF Noob!

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    Hehe.
     
  11. RyanLilly

    RyanLilly No longer a newbie, moving up!

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    I would zoom, just not in THAT fashion.
     
  12. musicaleCA

    musicaleCA TPF Noob!

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    Uh...huh. Well I zoom like mad sometimes in sports, just to see what the heck is going on without moving my eye away from the viewfinder. Or sometimes the play moves so fast that I have to zoom out or in quickly. It happens.

    The world of modern film is one of primes, you know.

    Anyway, this whole "problem" sounds like newbies to photography picking up 7D's hot off the shelf and not knowing how the camera works. :lol: (No offence to the op intended.)
     

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