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  1. #21
    David Brown's Avatar
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    Why be normal? :rolleyes:

  2. #22
    Ole
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    Quote Originally Posted by Ed Sukach View Post
    Wooop!!! My apologies to Ole -- I misread "Eh" as "Ed", and I thought he was taking issue with MY post!
    No worries ed, you've never been an "Eh".

    "Back at the beginning", most lenses for 35mm film were Tessar and Tessar derivatives - take a loot at the Leitz Elmars, for example. a really fast Tessar, say an f:2.8, is very inadequate at a focal length equal to the frame diagonal at full aperture. They're still not much good after reducing the stated coverage by a couple of degrees, but they are a lot less objectionable.

    "Normal" lenses for other formats tend to be very close to the frame diagonal; only the 35mm 24x36mm frame size is an exception. This could be due to several different things: 1) The need for fast, sharp lenses caused a 50mm standard since a 43mm with sharp corners at full aperture was too difficult.
    2) Due to the narrower aspect ratio, a slightly longer focal length gives a more "normal" width" to the resulting frame.

    Or maybe 3) - the first lens Leitz made for the Leica was a 50mm...


    BTW, "absinthe's" original calculations seem to have been made under the influence of his namesake drink: Please remember that frame sizes are not equal to nominal size, and that there are 25.4mm in an inch.
    -- Ole Tjugen, Luddite Elitist
    Norway

  3. #23
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    DISREGARD PREVIOUS POST - Incorrect info. - THIS POST IS CORRECT NOW.

    The original poster just wanted a rough rule of thumb. Walter23 was correct in providing the Pythagorean Theorum formula for determining the diagonal for each format size, and as a result, pretty close to the focal length.

    For myself, when using various formats (4x5, 6x9, 6x12) with my view camera, I find it helpful to have a table using Walter's formula, and then converting that mm value (I measure each format in mm - even 4x5) into a magnification value. For example, as 50mm is the standard for 35mm, a 200mm would have a magnification of 200/50 or 4x. By setting up similar magnification values for various formats, I have an almost "apples to apples" comparison for quick referral in the field (i.e. best lens choice for what I want depending on format being shot). I know there are more complex 35mm equivalent tables about, but the above concept has served me well.


    " Be happy. Take a silver break today !!!"
    MP_Wayne

  4. #24

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    Hmm, well I was assuming that "Normal" meant something. I am not asking what is your prefered lens, or default lens and bes tlens for a job. But what exactly is "Normal". The fact that someone decided it should be the same focal length as the widest part of the image (diagonal) suggests something. I am sure there will be some reference to circles of confusion and all such things, but there is something interesting abotu the focal length and the diagonal being somehow similar. I mean, does a 300 mm lens project a 300 mm circle at 300 mm away at some particular f-stop or is it all just arbitrary? Certainly an inappropriately short lens will not project into the corners of the image, though perhaps that is a matter of other things?

  5. #25
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    Quote Originally Posted by Ed Sukach View Post
    Wooop!!! My apologies to Ole -- I misread "Eh" as "Ed", and I thought he was taking issue with MY post!
    Eh?

  6. #26

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    If you like formulas here you go. Just enter the values in the white areas and read them the way you like in the colored areas.
    Attached Files

  7. #27
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    To me, "normal" approximates human vision for given format excluding periphery. IDK how that relates to "normal" according to calculated norms of normal, (probably calculated by some guy named Norm) that just always how I have thought of it. I guess there is "official normal" or maybe "accepted normal" and "personal normal" as illustrated by the 47mm on 4x5 suggestion.

  8. #28

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    There are some remarkable examples of obfuscating a simple question here. A normal lens is "normal" because it approximates the perception of the human eye. This is often regarded as the field of view of a single eye, but this is a pretty confusing way to look at it. The human eye cannot view a static image - that's not the way the eye/brain combination works. The eye actually scans a scene, while the brain constructs an image from the scan. If you try to perceive the limits of your field of view, your eye will involuntarily begin scanning a larger field of view, making the exercise impossible.

    A better way of looking at it is with reference to perspective. A wide angle lens exaggerates perspective, causing near objects to be proportionately larger and far objects to be proportionately smaller. A telephoto lens compresses perspective, which is why the pitcher and batter appear to be the same size when watching baseball on TV. Even though the pitcher and batter are about 60 ft apart, the camera is a lot further away than that and using a telephoto lens. A normal lens produces normal perspective. Olympus lists 8mm - 35mm as wide angle, 40mm - 55 mm as normal, 85mm and longer as telephoto. (These are OM lenses).

  9. #29

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    Ok, that makes sense, but why is the relationship the same between the focal length as the diagonal?

  10. #30

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    I've realised that this may be a more appropriate thread for the imaginary conversation I made up concerning normal lenses. I wish to say that I was thinking 24" Artar, I'm not even sure there is a 48", and in my defence I have had a lot of caffeine today, along with a slight fever!

    For your reading pleasure...

    - Justin

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