Apperture question

Discussion in 'Photography Beginners' Forum' started by ketan, Sep 14, 2007.

  1. ketan

    ketan TPF Noob!

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    With my limited experience and knowledge I believe that the usage of focal length below 4.0 are mainly for a very specific purposes and not to be used for general purposes as I experienced that it creates sometimes unnecessary bokeh. So, if I have couple of primes of 2.8 then I can settle for a lens with f 4 in the range of 70+
    Correct me if my understanding is not right
    Thanks
     
  2. EOS_JD

    EOS_JD TPF Noob!

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    I think you need to read "Understanding Exposure" by Bryan Petersen. You will understand then when to use aperture values larger than f4.

    You mean apertures larger than f4. (focal length relates to magnification).

    Well yes. Larger apertures are used to isolate subjects, provide faster shutter speeds, to provide enough depth of field (amount in focus).

    If you try to use a smaller aperure, you may find that the shutter speeds will be too slow for you to take the shot! Using a large aperture does mean smaller depth of field but you can control this by changing your distance to the subject and using a wider lens.

    So remember that longer lenses require faster shutter speeds to remove camera shake. 1/fl is the rule where fl = focal length. Transfer this to a 200mm lens. You'll need at least 1/200th to get a sharp image. In order to get this f4 may be too slow so f2.8 or faster may be required.[/quote]

    As I say read the book "Understanding Exposure" and all will become clearer.
     
  3. Big Mike

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

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    Have a lens with a larger maximum aperture is almost always better. It gives you the option to use those large aperture...but you can always 'stop the lens down' to a smaller aperture when you want to.

    The problem with lenses that have smaller maximum apertures...is that you don't have the option of using larger apertures when you may need it, which is more often that you may think.

    As EOS JD mentioned, it would really help to sit down with a good book and read up on how all these things are tied together.
     
  4. ketan

    ketan TPF Noob!

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    Sure Seniors, as you have mentioned I already have purchased two books by Mr.Bryan Peterson - (1) Leaning to see creatively and (2)Understanding Exposure.
    I thought of first making my composition principles right so I have started with the first one.
    EOS_JD, I used word focal length wrongly in place of apperture value. I will practice more on these terminologies. (I am used to debits and credits.:mrgreen:)
    Quote:
    EOS_JD-If you try to use a smaller aperure, you may find that the shutter speeds will be too slow for you to take the shot! Using a large aperture does mean smaller depth of field but you can control this by changing your distance to the subject and using a wider lens.
    Unquote:
    This is E=mC2 for me but will read more and try to crack it.
    Quote:
    EOS_JD-So remember that longer lenses require faster shutter speeds to remove camera shake. 1/fl is the rule where fl = focal length. Transfer this to a 200mm lens. You'll need at least 1/200th to get a sharp image. In order to get this f4 may be too slow so f2.8 or faster may be require
    Unquote:
    It never occured to me that composition of bokeh will be different at 200mm compared to 50mm. So at 50mm while trying to shoot a palm tree base I see output with some funny bokeh which may not be there at 200mm.-Eureka.
    [​IMG]
    Thanks guys
    ketan
     
  5. EOS_JD

    EOS_JD TPF Noob!

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    The area that is out of focus changes dependant on distance to subject, aperture used and focal length.

    Check out an online "depth of field calculator" which you can use to calculate the depth of field so that you know what settings would give you a certain subject all in focus.
     

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