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  1. #1

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    What is a Normal lens?

    As I understood it, the "normal" lens was based on the diagonal of the film format. However, when I calculate these, I never get a normal lens that I am used to hearing:


    H W Diag ?Customary Normal?
    24 36 43.26661531mm ------------ 50mm?
    4 5 6.403124237" --------------- 7"?
    8 10 12.80624847" -------------- 13"?
    2.25 2.25 3.181980515cm ---- 31.49 = 80 mm?
    6 6 8.485281374cm ------------ 80 mm?
    2.25 2.75 3.553167601" (90.25) ------ 90 mm?
    6 7 9.219544457cm ------------ 90 mm?
    6 9 10.81665383cm ----------- 100 mm?
    2 3 3.605551275" (91) -------- 90 mm?

    Is there something you do after you come up with the diagonal to get to the "normal" lens or is it just easier to deal with the next size up?

    Some seem close, while others are not so close.

  2. #2
    Ian Grant's Avatar
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    It's very rule of thumb, and the formats have different aspect ratios.

    So:
    35mm - 50 -55mm
    6x4.5 - 80mm
    6x6 - 75 -80mm
    6x7 -90mm
    6x9 105mm
    5x4 -150mm
    10x8 300mm

    Ian

  3. #3
    Michel Hardy-Vallée's Avatar
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    Bear in mind that a nominal "50mm" lens could in fact be a 51.7mm or whatnot. Manufacturers round up numbers, which makes it easier for us customers to remember them more easily.
    Using film since before it was hip.


    "One of the most singular characters of the hyposulphites, is the property their solutions possess of dissolving muriate of silver and retaining it in considerable quantity in permanent solution" — Sir John Frederick William Herschel, "On the Hyposulphurous Acid and its Compounds." The Edinburgh Philosophical Journal, Vol. 1 (8 Jan. 1819): 8-29. p. 11

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  4. #4

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    i know some say it's the diagonal of the film format, but to me a normal lens is what i see with my eye. so it's 14mm for 35mm format and 47mm for 4x5.

    still others say that a normal lens is any lens that is neither telephoto or retrofocus, that the lens center to film plane is the same as the actual focal length. so then you can talk about performance from a normal 360mm lens versus a telephoto 360mm lens that would be smaller. there are also normal ultra-wides versus retrofocus ultra-wides on rangefinder cameras. on SLRs all wide angle lenses are retrofocus and all long lenses are telephoto so this definition of normal lens is no longer useful in the modern SLR era.

  5. #5

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    So the factor is just coming to a "nice sounding" number?

  6. #6
    Michel Hardy-Vallée's Avatar
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    Well, do you think you would sell more 51.7mm lenses or more "50mm" lenses?
    Using film since before it was hip.


    "One of the most singular characters of the hyposulphites, is the property their solutions possess of dissolving muriate of silver and retaining it in considerable quantity in permanent solution" — Sir John Frederick William Herschel, "On the Hyposulphurous Acid and its Compounds." The Edinburgh Philosophical Journal, Vol. 1 (8 Jan. 1819): 8-29. p. 11

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  7. #7

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    Pentax makes a 43mm.

    But "normal" tends to take into account a few other factors. 35mm film is small so a little longer lens seems a better choice. Mamiya for the RB/RZ went longer. 127mm or 110mm. I wonder if the 127mm was chosen because it was a common LF length? OTOH Fuji went a little wider using 90mm for it's later 6x9s.

    For sheet film if you use imperial then your calculated numbers are much closer. 12" on 8x10. 6 or so inches on 4x5. Factor in the film rebate and I bet it gets even closer.

  8. #8
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    Nick,I think, but sure don't know, that SLR's tend toward a slightly longer 'normal' and RF's tend toward slightly shorter 'normals' as the camera designs and usage better accommodates the respective lengths.

    *

  9. #9

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    I was thinking that for 35mm but wasn't sure how much it mattered for larger cameras.

    Fuji's used a longer lens IIRC on the 6x9 that didn't have the fixed lens.

  10. #10

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    Well, there is a factor I missed, what is the actual nominal measurements of the different formats?

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