Aperture and Focal length

Discussion in 'Beyond the Basics' started by Tennessee Landscape, Jan 31, 2008.

  1. Tennessee Landscape

    Tennessee Landscape TPF Noob!

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    Why would a 300 or 200mm lense at f/2.8 be so much more expensive than one at f/4.5 - 5?
     
  2. JDS

    JDS TPF Noob!

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    The first (main) thing is that it has a larger aperture and lets in more light allowing a faster shutter speed. Another is that it is f/2.8 throughout the entire focal range rather than getting smaller at longer focal lengths.

    Lenses with larger apertures typically also are built better all around - better glass, better build, better mount, etc.
     
  3. Tennessee Landscape

    Tennessee Landscape TPF Noob!

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    I understand the aperture, but I don't understand why a lenses that shoot with a larger aperture cost so much more than there counterparts....
     
  4. JDS

    JDS TPF Noob!

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    Yeah, I should probably retract my 'main' statement. What makes it cost more is mostly that these lenses are generally built better all around as I said in my last statement...
     
  5. Big Mike

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

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    The F number is a ratio of the focal length and the diameter of the aperture.

    So a 50mm lens at F2, would have an aperture diameter of 25mm.

    A 200mm lens at F2.8 would have and aperture diameter of 71mm. A 300mm at F2.8 would be 107mm.

    Those large apertures require large pieces of glass, large aperture blades etc. All this makes the lenses big, heavy and expensive.

    Also, as mentioned, the build quality is usually higher, with these lenses....which adds more to the price as well.
     
  6. Tennessee Landscape

    Tennessee Landscape TPF Noob!

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    Ok, fine....Still though....Why would I want one over the other as fas as taking pictures is concerned?
     
  7. Big Mike

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

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    Do some reading on 'basic exposure'.

    The aperture that you use, is directly related to the shutter speed (and ISO) that you use. So if you want a faster shutter speed (to freeze movement) then you need a large aperture.

    Also, the aperture controls the Depth of Field, so if you want a shallow DOF, you will want a large aperture.
     
  8. That One Guy

    That One Guy TPF Noob!

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    i went thru this same thing when i was looking to upgrade to an L lens.

    the 2 offered were:
    70-200mm f4.0L @ $550
    70-200mm f2.8L @ way too damn much for me to buy and still be married!

    the only real difference was aperture. build was the same. the f2.8 just had bigger glass.

    so i figured go with the f4.0, keep my marriage, and buy a flashlight for low light situations :mrgreen:
     
  9. Sandspur

    Sandspur TPF Noob!

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    The answer is that it's a lot more difficult - and expensive! - to craft a lens that large, and all the internal elements as well.

    Nikon and Canon only do this using the highest quality glass they can produce, and with extreme attention to every detail of design and construction.

    Also, they are very aware that the people most likely to buy these lenses are Pros and advanced amateurs. And we're a pretty picky lot!

    After all, our livelihood depends on the quality of our product. In order to meet our standards, the manufacturers are going to produce the highest quality equipment they can ... and they know we're going to pay for the quality of what we get.
     
  10. Tennessee Landscape

    Tennessee Landscape TPF Noob!

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    Thanks for the lesson, I understand the relationship between aperture, ISO, shutter speed, and DOF....I think you are missing what I'm asking.....


    Do you think that with my equipment ( listed in my signature ) will be suitable to take some hockey pictures? I was planning on starting with these settings and working from here.....ISO 1600, 1/200
     
  11. Big Mike

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

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    If you really understood...why would you ask this?...
    I'm not trying to be an @ss....but it seems fairly straight forward that a larger aperture will allow you to use a faster shutter speed...which is very, very important for many shooting situations.

    For example, say I was shooting hockey with a 300mm F2.8 lens. My shutter speed might be 1/200. If you where shooting at F5.6, your shutter speed would be 1/50 (1/60)...which would probably make it hard to get sharp shots.

    As for shooting hockey, the lighting in arenas is typically bad...even though it looks fairly bright. Plus, the action is quite fast....so to get shots that are not blurry, you need to use a fast shutter speed.

    You would be be fairly limited at F5.6...shooting at ISO 1600 will help, but that will mean a fair bit of noise.
     
  12. Tennessee Landscape

    Tennessee Landscape TPF Noob!

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    1.Because I want to know, why the difference in price...giving me a lesson in exposure does not answer my question..... 2. DUH 3. Thank you for answering my last question.
     

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