Fast lens

Discussion in 'Beyond the Basics' started by Harpua, Jan 29, 2006.

  1. Harpua

    Harpua TPF Noob!

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    I have heard the term fast lens a bunch since being on this forum, but I am not sure I know what it means. I think it has something to do with f numbers, but I do not have a good grasp yet on those either so I was hoping someone could give me a good simple definition of what makes a lens fast (or slow). Thanks.
     
  2. Polygon

    Polygon TPF Noob!

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    The lower the minimum f-number the faster the lens. A low f-number means a bigger aperture which lets more light coming in. Having more light in the same time means that you can user shorter shutter-speeds (or faster shutter-speeds from which the word "fast lens" orginates I think).
     
  3. Harpua

    Harpua TPF Noob!

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    Oh OK I think I get it. So the faster the shutter speed can go which is in direct relation to the lower the f number gives you a fast lens. Thanks Polygon.
     
  4. 'Daniel'

    'Daniel' TPF Noob!

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    Maybe I misunderstand you but I don't think you have quite got it. The shutter speed is determined by the body and the minimum shutter speed does not change depending on the lens you use.

    A fast lens means it has/ can have a large aperture (lets in alot of light). Shutter speeds are not involved. Unless you mean the shutter speeed can be faster and the photo still be correctly exposed then yes I know what you mean.
     
  5. Harpua

    Harpua TPF Noob!

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    OK I think I was making it more complicated then it needed to be. So basically, the smaller the f number, the faster the lens. And that will allow you to use a faster shutter speed if your camera allows that.
     
  6. 'Daniel'

    'Daniel' TPF Noob!

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  7. Digital Matt

    Digital Matt alter ego: Analog Matt

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    Yes, fast lenses have a wider maximum aperture, to allow more light in, which allows for a faster shutter speed, which can come in handy in low light situations, or when freezing motion.
     
  8. Torus34

    Torus34 No longer a newbie, moving up!

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    f is simply focal length divided by aperture.

    Anything below say, f3.5 can be considered as fast.
     

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