A Modest Proposal

Discussion in 'Digital Photography' started by Joseph Meehan, Jun 20, 2006.

  1. Let's face it. The current system of using 35mm equivalent focal
    lengths or crop/magnafication factors or things like 12X zoom to describe a
    lens/camera is not very clear to most users.

    I suggest (and I know the manufacturers and their Madison Avenue
    agencies will never accept) that all lenses be identified by their true
    focal length and all zoom lenses also be further identified by two numbers,
    one representing their wide end and one the telephoto end magnification.
    For example a 35mm x 100mm lens on a camera with as 1.5 crop factor camera
    would be ID'ed as

    35mm (1.11 X) - 100mm (3.13 X) indicating a near normal to about 3X
    zoom with NO wide angle.



    --
    Joseph Meehan

    Dia duit
    Joseph Meehan, Jun 20, 2006
    #1
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  2. Joseph Meehan

    Kinon O'Cann Guest

    Why not just list angles of view? Focal lengths, given the size differences
    in sensors, doesn't make sense but the angle of view does. Just list it in
    degrees, like 74 to 4 to describe a lens that goes from wide to tele. This
    way, when you compare two "ultra zooms" that differ by many millimeters you
    can see the real difference, the change in angle of view.

    "Joseph Meehan" <> wrote in message
    news:e5Rlg.62000$...
    > Let's face it. The current system of using 35mm equivalent focal
    > lengths or crop/magnafication factors or things like 12X zoom to describe
    > a lens/camera is not very clear to most users.
    >
    > I suggest (and I know the manufacturers and their Madison Avenue
    > agencies will never accept) that all lenses be identified by their true
    > focal length and all zoom lenses also be further identified by two
    > numbers, one representing their wide end and one the telephoto end
    > magnification. For example a 35mm x 100mm lens on a camera with as 1.5
    > crop factor camera would be ID'ed as
    >
    > 35mm (1.11 X) - 100mm (3.13 X) indicating a near normal to about 3X
    > zoom with NO wide angle.
    >
    >
    >
    > --
    > Joseph Meehan
    >
    > Dia duit
    >
    Kinon O'Cann, Jun 20, 2006
    #2
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  3. Joseph Meehan

    Pat Guest

    It's a slow week in the NG when this is the most exciting topic anyone
    can think of.

    .... and if this is the biggest thing on your mind, well, then I don't
    know what to say. It's never bother me enough to give a darn about.

    Gee, I think you should do it, but require a filter on the end of every
    lens. :)))



    Joseph Meehan wrote:
    > Let's face it. The current system of using 35mm equivalent focal
    > lengths or crop/magnafication factors or things like 12X zoom to describe a
    > lens/camera is not very clear to most users.
    >
    > I suggest (and I know the manufacturers and their Madison Avenue
    > agencies will never accept) that all lenses be identified by their true
    > focal length and all zoom lenses also be further identified by two numbers,
    > one representing their wide end and one the telephoto end magnification.
    > For example a 35mm x 100mm lens on a camera with as 1.5 crop factor camera
    > would be ID'ed as
    >
    > 35mm (1.11 X) - 100mm (3.13 X) indicating a near normal to about 3X
    > zoom with NO wide angle.
    >
    >
    >
    > --
    > Joseph Meehan
    >
    > Dia duit
    Pat, Jun 20, 2006
    #3
  4. Joseph Meehan

    Guest

    Joseph Meehan wrote:
    > Let's face it. The current system of using 35mm equivalent focal
    > lengths or crop/magnafication factors or things like 12X zoom to describe a
    > lens/camera is not very clear to most users.


    Didn't we just have this discussion in another thread?

    > I suggest (and I know the manufacturers and their Madison Avenue
    > agencies will never accept)


    ??? Because, what, the camera companies are colluding to make things
    deliberately confusing? Why, exactly, do you think they'd be opposed to
    making photography more accessible? My experience has been that
    technology companies tend to lean towards marketing that makes things
    less "confusing" even if it means obscuring the true techincal
    information.

    > ...that all lenses be identified by their true
    > focal length and all zoom lenses also be further identified by two numbers,
    > one representing their wide end and one the telephoto end magnification.


    Well, all lenses -are- identified by their true focal length, so we're
    already halfway to your modest proposal.

    > For example a 35mm x 100mm lens on a camera with as 1.5 crop factor camera
    > would be ID'ed as
    >
    > 35mm (1.11 X) - 100mm (3.13 X) indicating a near normal to about 3X
    > zoom with NO wide angle.


    Two questions here...

    First, are you proposing that every lens be marked with multiple values
    to satisfy all the different film/sensor sizes? Canon makes lenses that
    fit on cameras with 35mm film/digital cameras as well as 1.3x crop and
    1.6x crop digital sensors...this proposal would require the lens to be
    labeled three different ways...never mind the problems that occur when
    Canon decides to make a new sized sensor four years later, and none of
    the old lenses are "properly" labeled.

    Second, 3.13X would be 3.13 times larger than...what? An arbitrary
    "normal"? Who gets to pick what normal is? On what grounds? I realize
    that a 50mm lens is generally considered "normal" on a 35mm camera, but
    there's nothing fundamental about that focal length that makes it "1X
    magnification". Nobody buying their first lens is going to have any
    accurate idea of what 1x represents anyway, so this isn't any more
    informative to the first-time camera buyer than saying "35mm".

    (On the other hand, given the title of this post, I suppose this may be
    an attempt at satire...)

    - Darryl
    , Jun 20, 2006
    #4
  5. Joseph Meehan

    Guest

    Kinon O'Cann wrote:
    > Why not just list angles of view? Focal lengths, given the size differences
    > in sensors, doesn't make sense but the angle of view does.


    Err...why? The angle of view changes depending on the sensor/film size.
    The focal length doesn't. The whole concept of "effective 35mm focal
    length" comes up because of the angle of view differences. A 50mm lens
    has roughly a 40 degree angle of view on 35mm film or a full frame
    sensor...and a 31mm angle of view on a 1.3x sensor...and a 25 degree
    angle of view on a 1.6x sensor. And in all three cases, the image
    circle projected by the lens has a wider angle of view, and is being
    cropped by the film/sensor...so angle of view isn't a property of the
    lens anyway; it's a property of the lens/camera combination.

    > Just list it in
    > degrees, like 74 to 4 to describe a lens that goes from wide to tele. This
    > way, when you compare two "ultra zooms" that differ by many millimeters you
    > can see the real difference, the change in angle of view.


    And that still conveys very little information to the inexperienced. If
    I tell a random non-photographer that I have a lens with an angle of
    view of 6.25 degrees, that's not going to be much more meaningful than
    saying it's a 200mm lens. You'd have to learn what 6 degrees of view
    looks like, just as you'd have to learn what a 200mm lens looks like,
    so there's almost no gain.

    (I say "almost" no gain because it will give an intelligent person a
    rough guess. 180 degrees versus 45 degrees versus 2 degrees is fairly
    straightforward.)

    But to reiterate: Angle of view is not a property of the lens. It's a
    property of the lens/camera combination, and therefore whatever is on
    the lens will either have to be on there multiple times with multiple
    values, or be inaccurate for anyone with the "wrong" camera. Focal
    length is an intrinsic property of the lens. It makes sense to write
    that on the lens...just as minimum focus distance and f-stops are also
    intrinsic properties of the lens.

    - Darryl
    , Jun 20, 2006
    #5
  6. Joseph Meehan

    Bill Funk Guest

    On Tue, 20 Jun 2006 08:01:00 -0400, "Kinon O'Cann"
    <> wrote:

    >Why not just list angles of view? Focal lengths, given the size differences
    >in sensors, doesn't make sense but the angle of view does. Just list it in
    >degrees, like 74 to 4 to describe a lens that goes from wide to tele. This
    >way, when you compare two "ultra zooms" that differ by many millimeters you
    >can see the real difference, the change in angle of view.


    Ok, but...
    I have a 30D. The field of view of, say, a 70-200mm zoom will be
    different on my 30D than it would be on, say, a D50. Or a 5D. Which
    field of view figures should be printed on the lens?

    The current system works.
    It's confusing at first, but is fairly easy to understand. Your
    sugestion doesn't work; there's not enough room on a lens to list all
    the fields of view it could present with different size sensors. :)

    >
    >"Joseph Meehan" <> wrote in message
    >news:e5Rlg.62000$...
    >> Let's face it. The current system of using 35mm equivalent focal
    >> lengths or crop/magnafication factors or things like 12X zoom to describe
    >> a lens/camera is not very clear to most users.
    >>
    >> I suggest (and I know the manufacturers and their Madison Avenue
    >> agencies will never accept) that all lenses be identified by their true
    >> focal length and all zoom lenses also be further identified by two
    >> numbers, one representing their wide end and one the telephoto end
    >> magnification. For example a 35mm x 100mm lens on a camera with as 1.5
    >> crop factor camera would be ID'ed as
    >>
    >> 35mm (1.11 X) - 100mm (3.13 X) indicating a near normal to about 3X
    >> zoom with NO wide angle.
    >>
    >>
    >>
    >> --
    >> Joseph Meehan
    >>
    >> Dia duit
    >>

    >

    --
    Bill Funk
    replace "g" with "a"
    Bill Funk, Jun 20, 2006
    #6
  7. Joseph Meehan wrote:
    > Let's face it. The current system of using 35mm equivalent focal
    > lengths or crop/magnafication factors or things like 12X zoom to describe a
    > lens/camera is not very clear to most users.
    >
    > I suggest


    Simply a bad idea. If you are this bored, go back and read Swift's
    treatise, and note how he presaged digital photography, all the time
    everyone thought he was merely clever.

    --
    john mcwilliams
    John McWilliams, Jun 20, 2006
    #7
  8. Joseph Meehan

    ASAAR Guest

    On Tue, 20 Jun 2006 08:00:19 -0700, Bill Funk wrote:

    > Ok, but...
    > I have a 30D. The field of view of, say, a 70-200mm zoom will be
    > different on my 30D than it would be on, say, a D50. Or a 5D. Which
    > field of view figures should be printed on the lens?


    The largest, which would in this case be the angle corresponding
    to what the 5D's sensor could capture.


    > The current system works.
    > It's confusing at first, but is fairly easy to understand. Your
    > sugestion doesn't work; there's not enough room on a lens to list all
    > the fields of view it could present with different size sensors. :)


    The current system doesn't work at all well. The lens would NOT
    have to list all fields of view. All that would be needed would be
    the angle (or field of view) as well as the maximum sensor size that
    the lens could be used with without vignetting. Those two datums,
    if presented to a camera body, should be sufficient for it to show
    numerically its own field of view (in degrees) as well as the
    effective focal length for any lens in its LCD display, should the
    photographer ever need to see it. Think of that, a camera that
    displays angular information. Next thing you know, there'd be a
    downloadable software module that would allow the camera to display
    the distance from golfer to putting green based on the flag height,
    just like those cheap Brookstone and Sharper Image yuppie gadgets
    do. Speaking of Sharper Image, you'd think that they could attach
    their brand name to their own line of cameras. They already do that
    for some of their other electronic products.
    ASAAR, Jun 20, 2006
    #8
  9. "Joseph Meehan" <> writes:

    > Let's face it. The current system of using 35mm equivalent focal
    > lengths or crop/magnafication factors or things like 12X zoom to describe a
    > lens/camera is not very clear to most users.
    >
    > I suggest (and I know the manufacturers and their Madison Avenue
    > agencies will never accept) that all lenses be identified by their true
    > focal length and all zoom lenses also be further identified by two numbers,
    > one representing their wide end and one the telephoto end magnification.
    > For example a 35mm x 100mm lens on a camera with as 1.5 crop factor camera
    > would be ID'ed as


    Can't be done, and you cite the reason right there -- lenses are used
    on cameras with different frame sizes, so you can't put the
    designation you want right on the lens.
    --
    David Dyer-Bennet, <mailto:>, <http://www.dd-b.net/dd-b/>
    RKBA: <http://www.dd-b.net/carry/>
    Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/>
    Dragaera/Steven Brust: <http://dragaera.info/>
    David Dyer-Bennet, Jun 20, 2006
    #9
  10. Joseph Meehan

    Guest

    ASAAR wrote:
    > The current system doesn't work at all well.


    Your opinion. When I started SLR photography a couple years ago, I
    found the system pretty easy to pick up. I didn't understand the
    reasons for it as well as I do now, but I quickly learned that 18mm was
    really wide and 70mm was a short-ish telephoto. (I have no idea what
    angles of view those correspond to.)

    > The lens would NOT
    > have to list all fields of view. All that would be needed would be
    > the angle (or field of view) as well as the maximum sensor size that
    > the lens could be used with without vignetting.


    What angle? The field of view of the image circle itself, or the FoV of
    the image circle after its been cropped by a 35mm (or some other)
    frame? These two numbers don't necessarily have any sort of linear
    relationship on a zoom lens. If you choose 35mm as your baseline, you
    start dealing in complete fiction when you need to show FoV for lenses
    that can't be used on 35mm frames. On the other hand, if you use "the
    largest standard sensor size that this lens works with", you'll have
    two lenses, one which says "50 degrees on 35mm" because it's a
    full-frame lens, and one that says "40 degrees on APS-C", because it's
    designed for a smaller sensor, and you have to do some really
    inconvenient math to figure out which of those is a wider-angle lens.

    > Those two datums,
    > if presented to a camera body, should be sufficient for it to show
    > numerically its own field of view (in degrees) as well as the
    > effective focal length for any lens in its LCD display, should the
    > photographer ever need to see it. Think of that, a camera that
    > displays angular information.


    Err...There's no reason that a camera can't do that now. My lenses
    communicate their focal length to the camera body. The camera body
    knows how big its sensor is. It can do the calculation; it's not hard.
    Heck, it could give me horizontal, vertical, and diagonal FoV values,
    just in case.

    Why doesn't it? Because it's completely pointless. Once I have the lens
    on the body, I can look through the viewfinder and actually -see- the
    field of view, which is infinitely more useful than reading a FoV value
    off the LCD.

    I agree that "75mm" is completely meaningless to someone with no
    experience in photography. But:
    - From a technical perspecitve, it makes sense
    - It's an inherent property of the lens that will never change
    and
    - It only takes a little experience to gain an understanding of what
    that means

    The major disadvantage is that it means different things on different
    bodies, but I have yet to hear of a reasonable alternative. I strongly
    suspect that Canon, or Fuji, or Nikon, or Olympus, or Sony, or any
    other camera company, would gladly put forward a new method of
    measuring lenses if they found one that made more sense. After all,
    these are the companies that sell compact cameras with "4x zoom"
    lenses, because "4x zoom" is easier to understand, even though it
    conveys far less meaning. Marketing likes things to be simple, because
    there's a huge market for simple things...but any half-serious
    photographer wants accurate information, and the focal length supplies
    that.

    - Darryl
    , Jun 20, 2006
    #10
  11. Joseph Meehan

    Ron Hunter Guest

    Joseph Meehan wrote:
    > Let's face it. The current system of using 35mm equivalent focal
    > lengths or crop/magnafication factors or things like 12X zoom to describe a
    > lens/camera is not very clear to most users.
    >
    > I suggest (and I know the manufacturers and their Madison Avenue
    > agencies will never accept) that all lenses be identified by their true
    > focal length and all zoom lenses also be further identified by two numbers,
    > one representing their wide end and one the telephoto end magnification.
    > For example a 35mm x 100mm lens on a camera with as 1.5 crop factor camera
    > would be ID'ed as
    >
    > 35mm (1.11 X) - 100mm (3.13 X) indicating a near normal to about 3X
    > zoom with NO wide angle.
    >
    >
    >

    Why not just require a calculation based on the area of the captured
    image at zoom, versus that at no zoom. Anyone can LOOK at the results
    and get meaningful information from that.
    Ron Hunter, Jun 20, 2006
    #11
  12. Kinon O'Cann wrote:
    > Why not just list angles of view? Focal lengths, given the size
    > differences in sensors, doesn't make sense but the angle of view
    > does. Just list it in degrees, like 74 to 4 to describe a lens that
    > goes from wide to tele. This way, when you compare two "ultra zooms"
    > that differ by many millimeters you can see the real difference, the
    > change in angle of view.


    That may even be better, but I would suggest a period of introduction
    since few people have any idea what the numbers would mean.

    >
    > "Joseph Meehan" <> wrote in message
    > news:e5Rlg.62000$...
    >> Let's face it. The current system of using 35mm equivalent focal
    >> lengths or crop/magnafication factors or things like 12X zoom to
    >> describe a lens/camera is not very clear to most users.
    >>
    >> I suggest (and I know the manufacturers and their Madison Avenue
    >> agencies will never accept) that all lenses be identified by their
    >> true focal length and all zoom lenses also be further identified by
    >> two numbers, one representing their wide end and one the telephoto
    >> end magnification. For example a 35mm x 100mm lens on a camera with
    >> as 1.5 crop factor camera would be ID'ed as
    >>
    >> 35mm (1.11 X) - 100mm (3.13 X) indicating a near normal to about
    >> 3X zoom with NO wide angle.
    >>
    >>
    >>
    >> --
    >> Joseph Meehan
    >>
    >> Dia duit


    --
    Joseph Meehan

    Dia duit
    Joseph Meehan, Jun 20, 2006
    #12
  13. Pat wrote:
    > It's a slow week in the NG when this is the most exciting topic anyone
    > can think of.
    >
    > ... and if this is the biggest thing on your mind, well, then I don't
    > know what to say. It's never bother me enough to give a darn about.
    >
    > Gee, I think you should do it, but require a filter on the end of
    > every lens. :)))
    >


    Which end or both ends??? :)

    --
    Joseph Meehan

    Dia duit
    Joseph Meehan, Jun 20, 2006
    #13
  14. Joseph Meehan

    Jim Guest

    "Joseph Meehan" <> wrote in message
    news:e5Rlg.62000$...
    > Let's face it. The current system of using 35mm equivalent focal
    > lengths or crop/magnafication factors or things like 12X zoom to describe
    > a lens/camera is not very clear to most users.
    >
    > I suggest (and I know the manufacturers and their Madison Avenue
    > agencies will never accept) that all lenses be identified by their true
    > focal length and all zoom lenses also be further identified by two
    > numbers, one representing their wide end and one the telephoto end
    > magnification. For example a 35mm x 100mm lens on a camera with as 1.5
    > crop factor camera would be ID'ed as
    >
    > 35mm (1.11 X) - 100mm (3.13 X) indicating a near normal to about 3X
    > zoom with NO wide angle.
    >
    >
    >
    > --
    > Joseph Meehan
    >
    > Dia duit
    >

    Why not just show the actual focal length? After all we didn't need such
    crutches as "35mm eqivalent" when so many of us deserted box or folding
    cameras for 35mm.

    Jim
    Jim, Jun 20, 2006
    #14
  15. "Jim" <> writes:
    > Why not just show the actual focal length? After all we didn't need such
    > crutches as "35mm eqivalent" when so many of us deserted box or folding
    > cameras for 35mm.


    Well, you need focal length and some characterization of image
    diameter. This approach might be useful anyways, since it would
    address situations like some of the cheap SLR wide angle lenses I have
    that aren't really useful at their nominal focal length due to
    horrible vignetting.

    --
    Richard W Kaszeta

    http://www.kaszeta.org/rich
    Richard Kaszeta, Jun 20, 2006
    #15
  16. Joseph Meehan

    Guest

    This is a good idea for a technical oriented person. However, it is
    more suitable
    for P&S camera than DSLR. It is more meaningful for P&S whose lens is
    fixed
    on the camera and cannot be changed. This topic has been discussed
    many times.
    The earliest one I responded was on Sep 17 2002. The following is a
    direct quote
    from that post in response to Mark Tranchant.

    You got the right idea. I use a slight different notation and add the
    actual focal length. The complete specification is the following

    2X optical zoom, .7X - 1.4X (actual focal length).

    Real example, Nikon CP-995

    Optical zoom 4X, .76x - 3.04x (8 - 32 mm). (end of quote)

    >From the responses on this topic, you can see how difficult it is to

    have
    a good idea accepted even on this news group. Someone even said
    directly that it is a bad idea.

    Charles S. Ih

    Joseph Meehan wrote:
    > Let's face it. The current system of using 35mm equivalent focal
    > lengths or crop/magnafication factors or things like 12X zoom to describe a
    > lens/camera is not very clear to most users.
    >
    > I suggest (and I know the manufacturers and their Madison Avenue
    > agencies will never accept) that all lenses be identified by their true
    > focal length and all zoom lenses also be further identified by two numbers,
    > one representing their wide end and one the telephoto end magnification.
    > For example a 35mm x 100mm lens on a camera with as 1.5 crop factor camera
    > would be ID'ed as
    >
    > 35mm (1.11 X) - 100mm (3.13 X) indicating a near normal to about 3X
    > zoom with NO wide angle.
    >
    >
    >
    > --
    > Joseph Meehan
    >
    > Dia duit
    , Jun 20, 2006
    #16
  17. "Joseph Meehan" <> writes:

    > I suggest (and I know the manufacturers and their Madison Avenue
    >agencies will never accept) that all lenses be identified by their true
    >focal length and all zoom lenses also be further identified by two numbers,
    >one representing their wide end and one the telephoto end magnification.
    >For example a 35mm x 100mm lens on a camera with as 1.5 crop factor camera
    >would be ID'ed as


    > 35mm (1.11 X) - 100mm (3.13 X) indicating a near normal to about 3X
    >zoom with NO wide angle.


    Lenses don't have a "magnification" on their own. The values you quote
    above (1.11 and 3.13) are relative to a lens of about 32 mm focal
    length, but where does *that* come from? Particularly since a single
    lens can be used on many different camera bodies with different sensor
    sizes.

    The only thing that makes sense to mark on a lens is *the
    characteristics of the lens itself that don't depend on the sensor
    size*. Those are:

    - true focal length, or focal length range for zooms
    - image circle diameter
    - maximum f/number (or f/number range for zooms)
    - zoom range for zooms (can be calculated from FLs, but it's useful on
    its own)

    So the lens above would be 35-100 mm 2.85X zoom with some maximum image
    circle (e.g. 43 mm if designed for "full frame") and f/number.

    Dave
    Dave Martindale, Jun 20, 2006
    #17
  18. Jim wrote:

    > Why not just show the actual focal length? After all we didn't need
    > such crutches as "35mm eqivalent" when so many of us deserted box or
    > folding cameras for 35mm.
    >
    > Jim


    That may be true for the regulars here, but for 90% of those who buy
    cameras, they don't understand.

    I do believe that a single standard way of presenting the information is
    needed for the large part of the market.

    --
    Joseph Meehan

    Dia duit
    Joseph Meehan, Jun 20, 2006
    #18
  19. ASAAR <> writes:
    >On Tue, 20 Jun 2006 08:00:19 -0700, Bill Funk wrote:


    >> Ok, but...
    >> I have a 30D. The field of view of, say, a 70-200mm zoom will be
    >> different on my 30D than it would be on, say, a D50. Or a 5D. Which
    >> field of view figures should be printed on the lens?


    > The largest, which would in this case be the angle corresponding
    >to what the 5D's sensor could capture.


    Yeah, but do you list the max horizontal field of view, max vertical
    field of view, or max diagonal field of view? The latter is the actual
    physical limit for the lens, while the other two depend on sensor aspect
    ratio, and *that* varies depending on camera design. But most
    photographers don't think in terms of diagonal FOV, even if they
    understand HFOV or VFOV.

    Dave
    Dave Martindale, Jun 20, 2006
    #19
  20. Joseph Meehan

    Kinon O'cann Guest

    <> wrote in message
    news:...
    > Kinon O'Cann wrote:
    >> Why not just list angles of view? Focal lengths, given the size
    >> differences
    >> in sensors, doesn't make sense but the angle of view does.

    >
    > Err...why? The angle of view changes depending on the sensor/film size.
    > The focal length doesn't. The whole concept of "effective 35mm focal
    > length" comes up because of the angle of view differences. A 50mm lens
    > has roughly a 40 degree angle of view on 35mm film or a full frame
    > sensor...and a 31mm angle of view on a 1.3x sensor...and a 25 degree
    > angle of view on a 1.6x sensor. And in all three cases, the image
    > circle projected by the lens has a wider angle of view, and is being
    > cropped by the film/sensor...so angle of view isn't a property of the
    > lens anyway; it's a property of the lens/camera combination.


    I wasn't referring to DSLRs. People who buy those cameras should already
    know, or be willing to learn the difference. Buyers of fixed lens cams can
    benefit from the angle of view listing.

    >
    >> Just list it in
    >> degrees, like 74 to 4 to describe a lens that goes from wide to tele.
    >> This
    >> way, when you compare two "ultra zooms" that differ by many millimeters
    >> you
    >> can see the real difference, the change in angle of view.

    >
    > And that still conveys very little information to the inexperienced. If
    > I tell a random non-photographer that I have a lens with an angle of
    > view of 6.25 degrees, that's not going to be much more meaningful than
    > saying it's a 200mm lens. You'd have to learn what 6 degrees of view
    > looks like, just as you'd have to learn what a 200mm lens looks like,
    > so there's almost no gain.


    So listing something as 5.1mm to 30mm makes sense? What does that tell you?
    Nothing. Unless you know the sensor size and can calculate the angles of
    view, millimeters are worthless.

    >
    > (I say "almost" no gain because it will give an intelligent person a
    > rough guess. 180 degrees versus 45 degrees versus 2 degrees is fairly
    > straightforward.)
    >
    > But to reiterate: Angle of view is not a property of the lens. It's a
    > property of the lens/camera combination, and therefore whatever is on
    > the lens will either have to be on there multiple times with multiple
    > values, or be inaccurate for anyone with the "wrong" camera. Focal
    > length is an intrinsic property of the lens. It makes sense to write
    > that on the lens...just as minimum focus distance and f-stops are also
    > intrinsic properties of the lens.


    OK, angle is a property of the lens when it's mounted on a fixed lens
    camera. For DSLR users, let them learn the difference.

    >
    > - Darryl
    >
    Kinon O'cann, Jun 20, 2006
    #20
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