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Thread: Queries on lenses

  1. #1
    Member lizter's Avatar
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    Mar 2003
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    Default Queries on lenses

    A couple of things which i cant figured out why. can somebody explains them to me

    1) How do i determine the min aperture of a lens when they always only show the max? eg : canon EF 28-90mm f/4-5.6 has a min aperture of f/22-32. Why is it not shown? is it not important?

    2) And why is it that the min & max aperture changes when i shoot at different focal length?

    3) I notice that the price of a lens gets higher as the aperture gets bigger. In the case of a wide angle lens, lets say a 24mm lens with f/2.8 is so much cheaper than one with f/1.4. why is this so?
    I understand that as the aperture gets bigger, the DOF gets shorter. isnt this the killer for landscape photographer who needs max DOF when they uses wide angle lenses. Then why is it that they wants to get a lens with a bigger aperture which costs so much more?

    4) What is the best way to test for the quality of a lens?
    How do i check whether is there any dust particles in the lens?

    5) Lastly, what does it mean by angle of view of lens, in term of diagonal, vertical and horizontal? and how do i read those degree?

    Thanks

  2. #2
    Senior Member
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    Default Re: Queries on lenses

    Originally posted by lizter
    1) How do i determine the min aperture of a lens when they always only show the max? eg : canon EF 28-90mm f/4-5.6 has a min aperture of f/22-32. Why is it not shown? is it not important?
    The minimum aperture of most lenses isn't critical, unless the lens is to be used for Macro (1:1 scale or larger) photography. What is more important is the maximum (widest) aperture as this determines the lens's ability to work in low lighting conditions, minimum depth of field distance etc.
    Originally posted by lizter
    2) And why is it that the min & max aperture changes when i shoot at different focal length?
    It's cheaper and easier to construct a ZOOM lens with variable aperture relative to focal length than a fixed aperture value which requires larger optical elements and a more advanced optical design.

    Thus a zoom of say 35-105mm with a f4.5/5.6 aperture is described thus.

    35mm f4.5
    105mm f5.6

    progressive variation between f4.5 and f5.6 for lengths between the two quoted values.

    Originally posted by lizter
    3) I notice that the price of a lens gets higher as the aperture gets bigger. In the case of a wide angle lens, lets say a 24mm lens with f/2.8 is so much cheaper than one with f/1.4. why is this so?
    Esssentially a fast lens costs more to produce, is heavier and requires a more complex optical design to correct for errors than a slower lens.

    some of the factors that increase lens cost as the lens gets 'faster'...

    Larger lens elements (more expensive)
    Larger body (more materials/expense)
    More optical correction (more expensive)
    Many other reasons ...

    Originally posted by lizter
    I understand that as the aperture gets bigger, the DOF gets shorter. isnt this the killer for landscape photographer who needs max DOF when they uses wide angle lenses. Then why is it that they wants to get a lens with a bigger aperture which costs so much more?
    For best results most landscape photographers use an aperture of between f11 and f16 to maximise the depth of field and keep an acceptable image quality.

    Low light use is the main reason to use a fast wide angle lens, also the the ability to have more control of DOF in some cases and in the case of a lot of Singapore Photographers, what's known as 'wanker appeal'.

    Originally posted by lizter
    4) What is the best way to test for the quality of a lens?
    Shoot with the lens, examine the results of test shots made at various apertures, shooting distances with a 40x or better microscope and use impeccable shooting techniques.

    Originally posted by lizter
    How do i check whether is there any dust particles in the lens?
    See other threads on this site dealing with this question

    Originally posted by lizter
    5) Lastly, what does it mean by angle of view of lens, in term of diagonal, vertical and horizontal? and how do i read those degree?
    It refers to the diagonal coverage from one lens corner to the other unless otherwise stated.
    The Ang Moh from Hell
    Professional Photography - many are called, few are chosen!

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