What does 'Fast' mean?

Discussion in 'Beyond the Basics' started by mhowel22, Mar 22, 2005.

  1. mhowel22

    mhowel22 TPF Noob!

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    When I see an advert with Fast lens mean. E.g. Fast 200mm.
     
  2. Hertz van Rental

    Hertz van Rental TPF Noob!

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    It means a large maximum aperture - which means a large piece of glass in front - which means you pay a lot more.
     
  3. tr0gd0o0r

    tr0gd0o0r TPF Noob!

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    It also means you can take photos in a lower light with a faster shutter speed.
     
  4. Kent Frost

    Kent Frost TPF Noob!

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    A fast 200mm lens would be something like a 200mm lens with a maximum aperture of 2.8.

    One that would not be as fast would be one with a maximum aperture of, say, 4.5. As you surely already know, the smaller the aperture number, or F-Stop, the wider open it can get, allowing more light income, thus letting you shoot, as said, with a faster shutter speed, which minimizes motion blur in the image caused from camera shake.
     
  5. ShutteredEye

    ShutteredEye TPF Noob!

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    How does this affect the other side of the coin? What differences are there between a "fast" and "slow" lens in the very small apertures?

    Also, if my camera as an f27 setting, does that mean any lens I attach to the body will shoot at f27?
     
  6. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    There is usually no difference. A "fast" lens just has a larger max aperture than a "slow" lens.
     
  7. willg133

    willg133 TPF Noob!

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    the way i think about it....if you have a lens that has a max aperature of 4.5 it won't perform as well at 4.5 as a lens with a max aperature of 2.8 or so....am i right?
     
  8. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    It is often said that a lens will be it's sharpest a couple of stops closed down from wide open. That is a popular generalization, but it may or may not be true, depending on the particular lens. There are always exceptions to the rule.

    The Nikon 50mm f/1.8 manual focus lens is said to be sharper at f/1.8 than the Nikon 50mm f/1.4 is at f/1.8

    There are folks who claim the 75mm f/3.5 planar on a Rollei TLR is sharper at f/3.5 than the 80mm f/2.8 version at f/3.5

    I'm sure there are folks who would debate these examples, but there are many, many posts on the internet saying it is so.
     
  9. Contra|Brett|

    Contra|Brett| TPF Noob!

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    yes and no.

    Generally the fast 2.8's are made of much higher quality glass then their 4.5 brethrin.
     
  10. KizaHood

    KizaHood TPF Noob!

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    I think not! If you attach some lens that has minimum aperture at f16, you won't be able to shoot at f27.

    So, you have the camera with f setting on it's body? As I know, such setting may work properly only if the lens supports using of that particular feature.

    For example, Nikon F-100 has f control on it's body. But if you attach for example Helios lens on F-100 body, the only way to set the aperture would be by operating aperture ring placed on the lens. If you set camera's f setting to f8 while aperture ring on Helios is set to f4, the camera will shoot at f4!

    Similar thing is with autofocus - you may use the autofocus feature only if you have an AF lens attached!
     
  11. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    That is definately what the salepeople are going to tell you ;) Their mantra is more money equals better stuff. Personal testing (or by a friend you trust) is really the only way to tell for sure.
     
  12. ShutteredEye

    ShutteredEye TPF Noob!

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    Hmm, good point. I just haven't ever noticed a lense advertising its upper f settings. Maybe I better check that out on my lenses.....
     

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