primes?

Discussion in 'Beyond the Basics' started by roadkill, Feb 21, 2008.

  1. roadkill

    roadkill TPF Noob!

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    I know I may sound like a dumbass... but what are/is primes when referring to lenses?
     
  2. nicfargo

    nicfargo TPF Noob!

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    they are lenses that have no zoom. Zoom lenses have a range that they can cover, for example 24-70mm. A prime would be 50mm. You cannot zoom...if you're too far away you must physically get closer to your subject.
     
  3. Helen B

    Helen B TPF Noob!

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    That's the most common meaning these days. A lens with a fixed, or nearly fixed, focal length. Some lenses do vary their focal length a little as they are focussed, but they are still called primes.

    The other meaning, much less common nowadays, is the main lens in a combination. For example you could have a lens fitted with a teleconverter, a wide angle converter, a varifocal converter, an anamorphic (squeeze) lens, a close-up lens (aka diopter) or other supplementary lens. The main lens would be referred to as the prime lens in that case.

    Best,
    Helen
     
  4. EOS_JD

    EOS_JD TPF Noob!

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    Helen
    Name a prime lens that varies it's focal length that is a prime? I think you may be confusing that the barrel may extend when focusing but this is different from focal length which remains constant.

    Prime = Fixed Focal Length
    Zoom = Variable Focal Length
     
  5. Happy Hour

    Happy Hour TPF Noob!

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    I believe Helen was referring to the distance when a lens focuses. Like my 50mm macro, depending on the subject when focusing it can lock on at 1 foot away or zoom in to 2 inches from the subject before it actually locks focus. Therefore the distance changes depending on where it focuses.
     
  6. Helen B

    Helen B TPF Noob!

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    No, I'm referring to the focal length of the lens.

    OK, so what would you call these three current AF Micro-Nikkors: the 60 mm, the 105 mm and the 200 mm? They all achieve their closest focus by shortening their focal length. The focal length cannot be changed independently of the focus setting. There may be other 'prime' lenses with internal focussing that change their focal length while focussing.

    There are a number of high-end motion picture prime lenses (eg Zeiss UltraPrime) that change their focal length while focussing. Think about those focus pulls you see in the movies. If the lens had a fixed focal length, you would see a slight zoom effect as the focus was pulled. We call it 'breathing', and good MP lenses should control it, particularly the wide angle lenses.

    Best,
    Helen
     
  7. roadkill

    roadkill TPF Noob!

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    what's the point of a prime? Seems like a lot of money to spend (500-3000 dollars) on a lens that you have to physically move your body to get correct and accurate focus.
     
  8. roadkill

    roadkill TPF Noob!

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    give me a zoom any day
     
  9. keith204

    keith204 No longer a newbie, moving up!

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    sharp and fast
     
  10. roadkill

    roadkill TPF Noob!

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    happy hour, I don't understand. Sorry. If what I understand these folks to be saying is true, when you have a fixed lens like that there is no playing room in regaurds to focus. Am I off track? All I own are 18-55 Nikkor and 70-300 Quantaray
     
  11. roadkill

    roadkill TPF Noob!

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    Are there fixed lenses with AF?
     
  12. roadkill

    roadkill TPF Noob!

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    Keith...what is sharp and fast about having to reposition yourself everytime you want a new shot?
     

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