What do you mean when you say a lens is fast?

Discussion in 'Beyond the Basics' started by LAW2, Sep 20, 2006.

  1. LAW2

    LAW2 TPF Noob!

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    This comes up when talking about prime lens that have a larger aperature (low Fstop 1.8. Are we talking about shutter speed because the aperature is so large?

    Sorry wrong forum. I don't know how to move it.
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    A fast lens or a fast aperture would be about F2.8 or bigger (F2.0, F1.8, F1.4 etc). On the surface, this does not refer to shutter speed...a fast lens is a fast lens...on or off the camera.

    Why do we call it fast? Probably because a wider aperture allows us to use a faster shutter speed.
     
  3. JEazy

    JEazy TPF Noob!

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    Because they let more light in faster than slower lenses?
     
  4. Rob

    Rob TPF Noob!

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    Often with camera lenses there are two options of the same focal length, for example a 70-200 f4.5-5.6 and a 70-200 f2.8. The one with the smaller f-number allows a wider aperture and costs a great deal more. They are often built better. We call them "fast" lenses, simply because they allow more light to be let through to the film/sensor and therefore the exposure can be faster (usually a desirable thing).

    Prime lenses, which do not zoom, often have fewer elements and a wider aperture, making them "faster" than an equivilent focal length zoom.

    Rob
     
  5. Soocom1

    Soocom1 TPF Noob!

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    Many lenses as described by Rob are also of the large element range for yet another but closely related reason:

    Faster lenses also allow the image to be much brighter, and thus makes the image more color saturated.
     
  6. THORHAMMER

    THORHAMMER TPF Noob!

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    also in low light you can focus a lot faster and more accurate with them and a good body in conjunction.... they dont hunt for focus very often unless your in total ddarkness....
     

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