"Normal" Lens

Discussion in 'Photography' started by Gary Morrison, Aug 14, 2003.

  1. Really bsaic question here: Is there any reasonably-precise mathematical
    formulation of what focal length constitutes a "normal" lens (i.e., the
    breakpoint between wide-angle and telephoto), or are numbers for that
    fundamentally approximate and conventional, and derived basically
    intuitively or inductively? I'd imagine that that could get interesting
    when you bring wide-screen media into the question, for example.
     
    Gary Morrison, Aug 14, 2003
    #1
    1. Advertisements

  2. Gary Morrison

    photo35744 Guest

    For 35 mm a normal lens is 50 mm for medium format it is 80 mm.
     
    photo35744, Aug 14, 2003
    #2
    1. Advertisements

  3. Gary Morrison

    Adam F Guest

    pentax reckons that based on the human AOV it's about 43mm


    adam f
     
    Adam F, Aug 14, 2003
    #3
  4. For 35 mm a normal lens is 50 mm for medium format it is 80 mm.

    Sure, and around 30 for my new D100.

    My question though is how those numbers are calculated, or whether they really
    even can be calculated.
     
    Gary Morrison, Aug 14, 2003
    #4
  5. Gary Morrison

    Brian Guest

    Sorry bud you lost me right after "For 35mm, yes", LOL
    Ok lets try this then,
    Ansel Adams defines a "Normal" lens as "one whose focal lenght is about
    equal to the diagonal of the film format. Such a lens will have an angle of
    view of about 50 degrees to 55 degrees, comparable to what we consider
    normal human vision. A 50mm (2-inch) lens is considered normal for 35mm
    cameras (although the actual film diagonal is about 42mm); 80mm is normal
    for 2 1/4 x2 1/14 format; and 150mm to 165mm is normal for 4x5."

    From his book The Camera.

    Brian.................
     
    Brian, Aug 14, 2003
    #5
  6. I did a dirty check on what was normal for my field of view, by taking a
    35mm camera with the lens on, and composing with one eye and looking out
    with the other. When what I saw in the viewfinder was what I saw with the
    open eye, I found the lens was at about 50mm!
     
    John Garrison, Aug 14, 2003
    #6
  7. Gary Morrison

    Frederick Guest

    I don't know any formula used to calculate it, but on a 35mm camera
    the standard "normal" lens is 50mm. Less would be Wide angle, and more
    would be telephoto or Zoom.
     
    Frederick, Aug 14, 2003
    #7
  8. Gary Morrison

    John O. Guest

    I think you should try a different forum for this one. A medical, math
    or science group would probably be better.
     
    John O., Aug 14, 2003
    #8
  9. Gary Morrison

    Jeremy Guest

    x-no-archive: yes
    The word "normal" refers to the lens' focal length--the distance between a
    point in the lens and the film when the lens is focused on infinity.

    A "normal" focal length lens on any camera is considered to be a lens whose
    focal length closely approximates the diagonal of the picture area produced
    on the film. With 35mm cameras this actually works out to be about 43mm,
    generally considered to be a little too short to produce the best angle of
    coverage and the most pleasing perspective. Makers of 35mm cameras have
    generally standardized on 50mm or 55mm as normal lenses. Pentax even made
    some normal lenses in 58mm.

    Pentax currently does have a 43mm normal lens in their "Limited" series, and
    it has gotten excellent reviews.
     
    Jeremy, Aug 14, 2003
    #9
  10. Hallo Gary,
    the definition of "normal lens" depends on the format of used picture
    format in camera and corresponds approximately to the diagonale of the slide
    / negative. This has been defined in the early days of photography and it
    was assumed, that this will simulate a natural view of the taken pictures,
    i.e. the perspective corresponds to the natural view angel of our eyes in
    real world.
    So, if you look at the most common slide/negative format of 36mm x 24 mm,
    the diagonale is calculated (due to the formula from Pythagoras): sqare root
    of (24*24 + 36*36) which gives something about 43. Actually the value of
    50mm is a rounded up one, I don´t know the reason for that now.
    Considering large format negatives / slides you should be aware of various
    available formats (6x4 cm, 6x6 cm, 6x9cm , 9x13 cm etc). So the individual
    "normal lens focal length" for large format cannot be given with one
    value...
    greetings Georg
     
    Sanda & Georg Polenik, Aug 14, 2003
    #10
  11. Gary Morrison

    Slingblade Guest

    Standard NOW...but in times past some camera makers have sold 45mm or
    55mm lenses as "standard" with their 35mm bodies. My understanding as
    someone else mentioned earlier in this thread is that approximately
    43mm would be considered technically "standard" since that most
    closely approximates the field of view of a single human eye.
     
    Slingblade, Aug 14, 2003
    #11
  12. Matching magnification doesn't seem to work for me on my D100 at least. When I
    matched the magnification of what I saw through my open eye with what I saw
    through the lens, it turned out to be 62mm, clearly too large when a normal
    lens is accepted to be around 30mm or thereabouts.

    Matching the height or width of the image appears to be the right approach,
    except, as in 70mm or IMAX where the image is specifically designed to involve
    a lot of peripheral-vision area.
     
    Gary Morrison, Aug 15, 2003
    #12
  13. I don't think that'll work for IMAX.
     
    Gary Morrison, Aug 15, 2003
    #13
  14. (The diagonal approach I mean.)
     
    Gary Morrison, Aug 15, 2003
    #14
  15. IMAX is clearly intended to be viewed much closer than a typical 35mm
    print. Its purpose is to entirely fill peripheral vision and to allow you
    to turn your head and see new stuff. So the diagonal doesn't quite work in
    that case, as far as I can tell, nor does the angle approach as such.
     
    Gary Morrison, Aug 15, 2003
    #15
  16. Hallo Gary,

    the focal length of a "normal lens" is defined as the diagonale of the
    slide / negative.
    This has been set up in the early days of photography and it was assumed,
    that this will
    simulate a natural view of the taken pictures, i.e. the perspective will
    correspond to the
    natural view angel of our eyes inreal world.

    So, if you look at the most common slide/negative format of 36mm x 24 mm,
    the diagonale is calculated (due to the formula of Pythagoras): sqare root
    of (24*24 + 36*36) which gives something about 43 (someone else has told us
    of such a lens
    from Pentax in this thread). Actually the value of 50mm is a rounded up
    one, I don´t know the
    reason for that now.
    Concerning large format negatives / slides you should consider the various
    available formats (6x4 cm, 6x6 cm, 6x9cm , 9x13 cm etc). So an individual
    "normal lens focal length" for large format is always associated with given
    conditions.
    greetings Georg
     
    Sanda & Georg Polenik, Aug 15, 2003
    #16
  17. Gary Morrison

    Jeremy Guest

    x-no-archive: yes
    You asked a question in a photographic newsgroup--we gave you the correct
    answer. If you are concerned with IMAX lens properties, you are in the
    wrong place.

    Most of us have never even seen an IMAX film, let alone know anything about
    the technical end.

    Normal is defined as a lens whose focal length is approximately equal to the
    diameter of the film. That has been THE textbook answer for many decades.
     
    Jeremy, Aug 15, 2003
    #17
  18. No, not the height or width of an object, but the height and width of the field
    of vision.

    The going theory is appears to be that human non-peripheral vision has a
    right-to-left (probably at least, rather than top-to-bottom) of around 50
    degrees. A hypothetical experiment for determining this would be:

    1. Tell somebody to stare straight ahead,
    2. Place one object to the right of that line of vision and one to the left,
    3. Gradually move those objects to the right and left,
    4. Stop when they say that the objects are clearly only in their peripheral
    vision field. That is, you stop when they report that it's iffy as to
    whether they even see it.
    5. A "normal" lens with the focal point right where your eyes are will put
    those objects right on edge of the frame.

    The angle at their eye between those two objects, allegedly at least will be
    between 48 and 55 degrees.
    I think the answer would be yes, but I certainly don't know that.
    That seems reasonable, except it certainly has to be measured in proportion to
    the size of the retina relative to the size of the film.

    Still, there has to be a factor related to how you're viewing the presentation
    of the picture as well. My illustration earlier was that, if you look at an
    IMAX frame printed on an 8x10 sheet of paper, it'll look very-wide-angle, but
    when viewed in the way it's intended to be viewed, muuuuch closer up, it'll
    look normal.
     
    Gary Morrison, Aug 15, 2003
    #18
  19. A hypothetical experiment for determining this would be...

    Or at least what I described here is what I interpret the concept to be.
    More likely it would be at a point where the object becomes hard to recognize,
    since we can see in our peripheral vision objects that we can't clearly recognize.
     
    Gary Morrison, Aug 15, 2003
    #19
  20. Gary Morrison

    J C Guest

    Let's put an end to this thread....

    I'd disagree with that statement. What's considered normal for any
    specific camera format does not equal what the human eye sees.
    Example, a 50 mm lens on a 35 mm does not capture the entire field of
    view of the human eye (i.e., from left to right periphery). In truth a
    "normal" lens is one that does not distort the image. For example,
    straight horizontal and vertical lines are captured on film as
    straight lines! The field of view is irrelevant.

    AND There is a formula for calculating a normal lens and that involves
    the ratio of the lens diameter to the focal length. Put another way,
    the normal lens is one wherein the focal length equals the diagonal of
    the image placed on the film.

    So here's the calculation using a 2.25 inch film format and the
    equation for a calculating the hypotenuse of a triangle:

    2.25 inches (squared) + 2.25 (squared) = the diagonal (squared)

    5.0625 + 5.0625 = diagonal (squared)

    The Square root of 10.125 = 3.1819

    Since this is in inches, convert to cm (using 1 inch = 2.54 cm) and

    3.1819 inches = 8.082 cm OR 80.82 mm

    So a normal lens for the 2.25 inch format is an 80 mm lens.

    However, note that there is actually a range (about +/- 5%) that would
    be considered normal because a lens will actually shine a circle of
    light and the only reason the camera takes square or rectangular
    pictures is because the camera's shutter is shaped that way. In some
    constructions the square or rectangle of the image will not form cords
    across this circle and therefore the diagnal of the image area on the
    film will be less than the diameter of the circle.


    -- JC
     
    J C, Aug 18, 2003
    #20
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.