A Rant re Focal Length Multipliers

Discussion in 'Digital Photography' started by C Wright, Jan 24, 2005.

  1. C Wright

    C Wright Guest

    Is anyone else bothered by the frequent use of "focal length multipliers" or
    "crop factors" when describing digital cameras and their lenses?
    Why don't the manufacturers just tell us what a "normal" lens is for a
    particular camera. If, for example, the manufacturers would tell us that a
    35mm lens is a normal lens for a particular digital camera we would know
    that we would need shorter lenses than that if we expected to get
    wide-angle. You would also know, of course, that anything longer than that
    would be moving toward telephoto.
    After all a 50mm lens is a 50mm lens is a 50mm lens (a rose is a rose is a
    rose)! It does not magically change to a 75mm lens on a digital camera with
    a focal length multiplier of 1.5.
    No one publishes the 35mm camera equivalent for an 80mm lens on a
    Hasselblad; no one publishes the 35mm camera equivalent for a 150mm lens on
    a 4x5 view camera!
    All of this I think adds to the confusion of new comers to the digital world
    who may go around thinking, for example, that the 200mm lens that they want
    to buy is really a 320mm lens on their 1.6 focal length multiplier camera.
    No it's not, it's a 200mm lens! The fact is that if you put that lens on a
    'full frame' 35mm camera and cropped a picture to the same size as a camera
    with a 1.6 focal length multiplier you would have exactly the same picture.
    There, I feel better!
    Chuck
    C Wright, Jan 24, 2005
    #1
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  2. C Wright

    Chris Brown Guest

    In article <BE1A6FB2.16B59%wright9_nojunk@nojunk_mac.com>,
    C Wright <wright9_nojunk@nojunk_mac.com> wrote:
    >Is anyone else bothered by the frequent use of "focal length multipliers" or
    >"crop factors" when describing digital cameras and their lenses?
    >Why don't the manufacturers just tell us what a "normal" lens is for a
    >particular camera.


    Some people can't get their head out of the 35mm mindset. Those of us who
    shoot multiple formats (digital "APS-C", 35mm, 6*6, 6*7 and 6*9 in my case)
    have no problem with the concept that a normal lens scales with capture
    diagonal, but the concept seems utterly alien to some.

    Witness the occasional person who thinks you can't use a 50mm lens as a
    portrait lens on a 24*16mm DSLR because "it will still have the perspective
    of a standard lens", or some such nonsense. Some of these people seem quite
    unshakable in their strange beliefs about the magical properties of various
    focal lengths.

    >No one publishes the 35mm camera equivalent for an 80mm lens on a
    >Hasselblad; no one publishes the 35mm camera equivalent for a 150mm lens on
    >a 4x5 view camera!


    Quite, but there seems to be an assumption amongst the camera manufacturers
    that those buying medium and large format equipment are generally not
    ignorant when it comes to this sort of thing (almost certainly justified),
    and that those who buy DSLRs might be (maybe justified, maybe not).

    Call it more evidence of "dumbing down" if you like, but I agree with you.
    If someone really can't understand the concept of focal length and how it
    relates to field of view, given varying format sizes, or just wants a camera
    for casual use and isn't interested in photography as an art form or
    occupation, you have to wonder if a sophisticated interchangable lens camera
    is really the right choice for them. Having said that, the manufacturers
    seem to think so, as many of them continue to put those point and shoot
    modes with the strange little icons of skiers and what-have-you on really
    quite high-end camera equipment.
    Chris Brown, Jan 24, 2005
    #2
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  3. C Wright

    bob Guest

    C Wright <wright9_nojunk@nojunk_mac.com> wrote in
    news:BE1A6FB2.16B59%wright9_nojunk@nojunk_mac.com:

    > Is anyone else bothered by the frequent use of "focal length
    > multipliers" or "crop factors" when describing digital cameras and
    > their lenses?
    >


    I think it's an easy to understand shorthand. So many people have so much
    experience with 35mm that understanding how the field of view will be
    different is a pretty useful thing.

    If you stipulate that 50mm is "normal" for 35mm film, then a Nikon D70
    would have a 33mm "normal" lens. If you already own a Nikon 24mm lens,
    and you want to know what kind of pictures to expect from a D70, what
    system would you suggest that would allow a person to know, other than a
    1.5 factor of some sort?

    Bob
    bob, Jan 24, 2005
    #3
  4. C Wright

    Jim Guest

    "C Wright" <wright9_nojunk@nojunk_mac.com> wrote in message
    news:BE1A6FB2.16B59%wright9_nojunk@nojunk_mac.com...
    > Is anyone else bothered by the frequent use of "focal length multipliers"

    or
    > "crop factors" when describing digital cameras and their lenses?

    Not particularly.
    > Why don't the manufacturers just tell us what a "normal" lens is for a
    > particular camera.

    Because they feel that their customers only understand the effect on the
    photo in terms of 35mm focal lengths.
    Jim
    Jim, Jan 24, 2005
    #4
  5. C Wright

    Bob Williams Guest

    C Wright wrote:
    > Is anyone else bothered by the frequent use of "focal length multipliers" or
    > "crop factors" when describing digital cameras and their lenses?
    > Why don't the manufacturers just tell us what a "normal" lens is for a
    > particular camera. If, for example, the manufacturers would tell us that a
    > 35mm lens is a normal lens for a particular digital camera we would know
    > that we would need shorter lenses than that if we expected to get
    > wide-angle. You would also know, of course, that anything longer than that
    > would be moving toward telephoto.
    > After all a 50mm lens is a 50mm lens is a 50mm lens (a rose is a rose is a
    > rose)! It does not magically change to a 75mm lens on a digital camera with
    > a focal length multiplier of 1.5.
    > No one publishes the 35mm camera equivalent for an 80mm lens on a
    > Hasselblad; no one publishes the 35mm camera equivalent for a 150mm lens on
    > a 4x5 view camera!
    > All of this I think adds to the confusion of new comers to the digital world
    > who may go around thinking, for example, that the 200mm lens that they want
    > to buy is really a 320mm lens on their 1.6 focal length multiplier camera.
    > No it's not, it's a 200mm lens! The fact is that if you put that lens on a
    > 'full frame' 35mm camera and cropped a picture to the same size as a camera
    > with a 1.6 focal length multiplier you would have exactly the same picture.
    > There, I feel better!
    > Chuck
    >
    >


    On all 35 mm film cameras the sensor size is FIXED at 24 x 36 mm.
    So all 35 mm camera users know immediately and instinctively whether a
    certain focal length lens is super wide angle, extreme telephoto or
    something in between.
    With Digicams the sensor size varies all over the place, from 24 x 35 mm
    in the Canon D1s to 3.34 x 4.45 mm in the Canon A400.
    So just telling you the focal length of your lens without also telling
    you the sensor size, doesn't give you a clue whether the lens is wide
    angle or tele when used with that particular camera. For instance, a
    F.L. of 28 mm on a D1s is a wide angle lens. On a Canon A400 that same
    focal length would be a strong telephoto.
    Bob Williams
    Bob Williams, Jan 24, 2005
    #5
  6. C Wright

    Bob Williams Guest

    Bob Williams wrote:
    >
    >
    > C Wright wrote:
    >
    >> Is anyone else bothered by the frequent use of "focal length
    >> multipliers" or
    >> "crop factors" when describing digital cameras and their lenses?
    >> Why don't the manufacturers just tell us what a "normal" lens is for a
    >> particular camera. If, for example, the manufacturers would tell us
    >> that a
    >> 35mm lens is a normal lens for a particular digital camera we would know
    >> that we would need shorter lenses than that if we expected to get
    >> wide-angle. You would also know, of course, that anything longer than
    >> that
    >> would be moving toward telephoto.
    >> After all a 50mm lens is a 50mm lens is a 50mm lens (a rose is a rose
    >> is a
    >> rose)! It does not magically change to a 75mm lens on a digital camera
    >> with
    >> a focal length multiplier of 1.5.
    >> No one publishes the 35mm camera equivalent for an 80mm lens on a
    >> Hasselblad; no one publishes the 35mm camera equivalent for a 150mm
    >> lens on
    >> a 4x5 view camera!
    >> All of this I think adds to the confusion of new comers to the digital
    >> world
    >> who may go around thinking, for example, that the 200mm lens that they
    >> want
    >> to buy is really a 320mm lens on their 1.6 focal length multiplier
    >> camera.
    >> No it's not, it's a 200mm lens! The fact is that if you put that lens
    >> on a
    >> 'full frame' 35mm camera and cropped a picture to the same size as a
    >> camera
    >> with a 1.6 focal length multiplier you would have exactly the same
    >> picture.
    >> There, I feel better!
    >> Chuck
    >>
    >>

    >
    > On all 35 mm film cameras the sensor size is FIXED at 24 x 36 mm.
    > So all 35 mm camera users know immediately and instinctively whether a
    > certain focal length lens is super wide angle, extreme telephoto or
    > something in between.
    > With Digicams the sensor size varies all over the place, from 24 x 35 mm
    > in the Canon D1s to 3.34 x 4.45 mm in the Canon A400.
    > So just telling you the focal length of your lens without also telling
    > you the sensor size, doesn't give you a clue whether the lens is wide
    > angle or tele when used with that particular camera. For instance, a
    > F.L. of 28 mm on a D1s is a wide angle lens. On a Canon A400 that same
    > focal length would be a strong telephoto.
    > Bob Williams
    >


    Errata;
    The full frame Canon EOS Digital SLR is called the 1Ds not the D1s
    Its sensor size is 24x36mm not 24x35mm
    Bob
    Bob Williams, Jan 24, 2005
    #6
  7. On Mon, 24 Jan 2005 11:33:59 -0800, Bob Williams
    <> wrote:

    >
    >
    >C Wright wrote:
    >> Is anyone else bothered by the frequent use of "focal length multipliers" or
    >> "crop factors" when describing digital cameras and their lenses?
    >> Why don't the manufacturers just tell us what a "normal" lens is for a
    >> particular camera. If, for example, the manufacturers would tell us that a
    >> 35mm lens is a normal lens for a particular digital camera we would know
    >> that we would need shorter lenses than that if we expected to get
    >> wide-angle. You would also know, of course, that anything longer than that
    >> would be moving toward telephoto.
    >> After all a 50mm lens is a 50mm lens is a 50mm lens (a rose is a rose is a
    >> rose)! It does not magically change to a 75mm lens on a digital camera with
    >> a focal length multiplier of 1.5.
    >> No one publishes the 35mm camera equivalent for an 80mm lens on a
    >> Hasselblad; no one publishes the 35mm camera equivalent for a 150mm lens on
    >> a 4x5 view camera!
    >> All of this I think adds to the confusion of new comers to the digital world
    >> who may go around thinking, for example, that the 200mm lens that they want
    >> to buy is really a 320mm lens on their 1.6 focal length multiplier camera.
    >> No it's not, it's a 200mm lens! The fact is that if you put that lens on a
    >> 'full frame' 35mm camera and cropped a picture to the same size as a camera
    >> with a 1.6 focal length multiplier you would have exactly the same picture.
    >> There, I feel better!
    >> Chuck
    >>
    >>

    >
    >On all 35 mm film cameras the sensor size is FIXED at 24 x 36 mm.
    >So all 35 mm camera users know immediately and instinctively whether a
    >certain focal length lens is super wide angle, extreme telephoto or
    >something in between.
    >With Digicams the sensor size varies all over the place, from 24 x 35 mm
    >in the Canon D1s to 3.34 x 4.45 mm in the Canon A400.
    >So just telling you the focal length of your lens without also telling
    >you the sensor size, doesn't give you a clue whether the lens is wide
    >angle or tele when used with that particular camera. For instance, a
    >F.L. of 28 mm on a D1s is a wide angle lens. On a Canon A400 that same
    >focal length would be a strong telephoto.


    I hate to be pedantic on this point but the focal length of the lens
    doesn't change with the size of the sensor. The crop size of the image
    changes. There is no change in the focal length.

    " the cropped area created by the multiplier factor increases the
    perceived (practical) focal length of the lens."

    Rest of article here.

    http://www.lonestardigital.com/multipler.htm



    ********************************************************

    "In general, the art of government consists in taking as
    much money as possible from one party of the citizens
    to give to the other."

    Voltaire (1764)
    John A. Stovall, Jan 24, 2005
    #7
  8. C Wright <wright9_nojunk@nojunk_mac.com> writes:

    > Is anyone else bothered by the frequent use of "focal length multipliers" or
    > "crop factors" when describing digital cameras and their lenses?
    > Why don't the manufacturers just tell us what a "normal" lens is for a
    > particular camera. If, for example, the manufacturers would tell us that a
    > 35mm lens is a normal lens for a particular digital camera we would know
    > that we would need shorter lenses than that if we expected to get
    > wide-angle. You would also know, of course, that anything longer than that
    > would be moving toward telephoto.


    I find the way they do it much more useful.

    > After all a 50mm lens is a 50mm lens is a 50mm lens (a rose is a rose is a
    > rose)! It does not magically change to a 75mm lens on a digital camera with
    > a focal length multiplier of 1.5.


    And the lens is labeled right on the front as a 50mm lens, so no
    problem there. And since I know my crop factor is 1.5 (Fuji S2), I
    can very quickly find that I get the angle of view I'd normally expect
    from a 75mm lens on a 35mm camera.

    > No one publishes the 35mm camera equivalent for an 80mm lens on a
    > Hasselblad; no one publishes the 35mm camera equivalent for a 150mm lens on
    > a 4x5 view camera!


    I've been photographing with cameras I could swap lenses on since
    1969. I currently own one 4x5 and two medium format, in addition to
    my 35mm equipment (5 film bodies plus the S2). I've previously owned
    several other medium format cameras. But you know what? I've never
    actually had a second lens for *any* of them except the 35mm cameras.
    Like the vast majority of photographers, my experience with focal
    lengths (as a decision) is 100% tied to 35mm work. I've got those
    numbers burned into my brain. Giving me the 35mm-equivalent numbers
    is the easiest way to give me that information.

    > All of this I think adds to the confusion of new comers to the
    > digital world who may go around thinking, for example, that the
    > 200mm lens that they want to buy is really a 320mm lens on their 1.6
    > focal length multiplier camera. No it's not, it's a 200mm lens! The
    > fact is that if you put that lens on a 'full frame' 35mm camera and
    > cropped a picture to the same size as a camera with a 1.6 focal
    > length multiplier you would have exactly the same picture. There, I
    > feel better! Chuck


    Glad you feel better. And of course anybody who really gets confused
    about focal lengths as opposed to angle of view has been badly served
    by their education and by the system. Which is why I prefer "crop
    factor" rather than "focal length multiplier".

    Meanwhile, I really enjoy my 450mm f2.8 lens and my 87.5 f1.2 NOCT.
    :)
    --
    David Dyer-Bennet, <mailto:>, <http://www.dd-b.net/dd-b/>
    RKBA: <http://noguns-nomoney.com/> <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, Jan 24, 2005
    #8
  9. In article <>,
    says...
    > On Mon, 24 Jan 2005 11:33:59 -0800, Bob Williams
    > <> wrote:
    > >
    > >On all 35 mm film cameras the sensor size is FIXED at 24 x 36 mm.
    > >So all 35 mm camera users know immediately and instinctively whether a
    > >certain focal length lens is super wide angle, extreme telephoto or
    > >something in between.
    > >With Digicams the sensor size varies all over the place, from 24 x 35 mm
    > >in the Canon D1s to 3.34 x 4.45 mm in the Canon A400.
    > >So just telling you the focal length of your lens without also telling
    > >you the sensor size, doesn't give you a clue whether the lens is wide
    > >angle or tele when used with that particular camera. For instance, a
    > >F.L. of 28 mm on a D1s is a wide angle lens. On a Canon A400 that same
    > >focal length would be a strong telephoto.

    >
    > I hate to be pedantic on this point but the focal length of the lens
    > doesn't change with the size of the sensor. The crop size of the image
    > changes. There is no change in the focal length.
    >
    > " the cropped area created by the multiplier factor increases the
    > perceived (practical) focal length of the lens."
    >
    > Rest of article here.
    >
    > http://www.lonestardigital.com/multipler.htm
    >
    >

    To be pedantic right back at you :)
    He didn't say that the focal length changed, just (correctly) that the
    sensor size determines whether a certain focal length is
    wide/normal/tele.
    Graeme Cogger, Jan 24, 2005
    #9
  10. C Wright

    C Wright Guest

    On 1/24/05 1:33 PM, in article , "Bob Williams"
    <> wrote:

    >
    >


    >> Why don't the manufacturers just tell us what a "normal" lens is for a
    >> particular camera. If, for example, the manufacturers would tell us that a
    >> 35mm lens is a normal lens for a particular digital camera we would know
    >> that we would need shorter lenses than that if we expected to get
    >> wide-angle. You would also know, of course, that anything longer than that
    >> would be moving toward telephoto.
    >>

    >
    > On all 35 mm film cameras the sensor size is FIXED at 24 x 36 mm.
    > So all 35 mm camera users know immediately and instinctively whether a
    > certain focal length lens is super wide angle, extreme telephoto or
    > something in between.
    > With Digicams the sensor size varies all over the place, from 24 x 35 mm
    > in the Canon D1s to 3.34 x 4.45 mm in the Canon A400.
    > So just telling you the focal length of your lens without also telling
    > you the sensor size, doesn't give you a clue whether the lens is wide
    > angle or tele when used with that particular camera. For instance, a
    > F.L. of 28 mm on a D1s is a wide angle lens. On a Canon A400 that same
    > focal length would be a strong telephoto.
    > Bob Williams
    >

    You apparently missed the point suggesting that manufacturers tell us what a
    "normal" lens is for a given camera - that then would be the starting point
    for determining whether a lens was wide-angle or telephoto for that
    particular camera.
    At the same I would agree with you and not for a second suggest that sensor
    size not be included in the specs. That would be important information for
    any knowledgeable buyer. It is just that I see new comers struggling with
    lens equivalencies!
    Chuck
    C Wright, Jan 24, 2005
    #10
  11. C Wright

    Guest

    In message <BE1A6FB2.16B59%wright9_nojunk@nojunk_mac.com>,
    C Wright <wright9_nojunk@nojunk_mac.com> wrote:

    >Is anyone else bothered by the frequent use of "focal length multipliers" or
    >"crop factors" when describing digital cameras and their lenses?
    >Why don't the manufacturers just tell us what a "normal" lens is for a
    >particular camera.


    Why aren't we using angles?

    That would make a lot more sense then refering to the focal length of
    lenses when what we are really interested in is the angle of view.

    The manufacturer could state the angle of view with a 50mm lens, or
    something like that.

    I hadn't used 35mm SLRs for almost 20 years when I started using 1.6x
    DSLRs. I relate directly to the absolute focal length in the context of
    these cameras, and I cringe when people refer to the "35-mm equivalent
    Angle of View" without stating such. Cropping does not effect focal
    length.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    , Jan 27, 2005
    #11
  12. wrote:
    > In message <BE1A6FB2.16B59%wright9_nojunk@nojunk_mac.com>,
    > C Wright <wright9_nojunk@nojunk_mac.com> wrote:
    >
    >> Is anyone else bothered by the frequent use of "focal length
    >> multipliers" or "crop factors" when describing digital cameras and
    >> their lenses?
    >> Why don't the manufacturers just tell us what a "normal" lens is for
    >> a particular camera.

    >
    > Why aren't we using angles?


    Based on what?

    - diagonal FOV, horizontal FOV, vertical FOV?
    - 4:3 aspect ratio, 3:2 aspect ratio?

    <G>

    David!
    David J Taylor, Jan 27, 2005
    #12
  13. C Wright

    Guest

    In message <>,
    "David J Taylor" <> wrote:

    > wrote:
    >> In message <BE1A6FB2.16B59%wright9_nojunk@nojunk_mac.com>,
    >> C Wright <wright9_nojunk@nojunk_mac.com> wrote:
    >>
    >>> Is anyone else bothered by the frequent use of "focal length
    >>> multipliers" or "crop factors" when describing digital cameras and
    >>> their lenses?
    >>> Why don't the manufacturers just tell us what a "normal" lens is for
    >>> a particular camera.

    >>
    >> Why aren't we using angles?

    >
    >Based on what?
    >
    >- diagonal FOV, horizontal FOV, vertical FOV?
    >- 4:3 aspect ratio, 3:2 aspect ratio?


    Any or all.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    , Jan 27, 2005
    #13
  14. C Wright

    Darrell Guest

    <> wrote in message
    news:...
    > In message <>,
    > "David J Taylor" <> wrote:
    >
    > > wrote:
    > >> In message <BE1A6FB2.16B59%wright9_nojunk@nojunk_mac.com>,
    > >> C Wright <wright9_nojunk@nojunk_mac.com> wrote:
    > >>
    > >>> Is anyone else bothered by the frequent use of "focal length
    > >>> multipliers" or "crop factors" when describing digital cameras and
    > >>> their lenses?
    > >>> Why don't the manufacturers just tell us what a "normal" lens is for
    > >>> a particular camera.
    > >>
    > >> Why aren't we using angles?

    > >
    > >Based on what?
    > >
    > >- diagonal FOV, horizontal FOV, vertical FOV?
    > >- 4:3 aspect ratio, 3:2 aspect ratio?

    >
    > Any or all.
    > --

    I believe he is suggesting angle of views, so refer to 64 degrees, or 72
    degrees etc...
    Darrell, Jan 28, 2005
    #14
  15. Darrell wrote:
    > <> wrote in message
    > news:...
    >> In message <>,
    >> "David J Taylor" <> wrote:
    >>
    >>> wrote:
    >>>> In message <BE1A6FB2.16B59%wright9_nojunk@nojunk_mac.com>,
    >>>> C Wright <wright9_nojunk@nojunk_mac.com> wrote:
    >>>>
    >>>>> Is anyone else bothered by the frequent use of "focal length
    >>>>> multipliers" or "crop factors" when describing digital cameras and
    >>>>> their lenses?
    >>>>> Why don't the manufacturers just tell us what a "normal" lens is
    >>>>> for a particular camera.
    >>>>
    >>>> Why aren't we using angles?
    >>>
    >>> Based on what?
    >>>
    >>> - diagonal FOV, horizontal FOV, vertical FOV?
    >>> - 4:3 aspect ratio, 3:2 aspect ratio?

    >>
    >> Any or all.
    >> --

    > I believe he is suggesting angle of views, so refer to 64 degrees, or
    > 72 degrees etc...


    What I'm also getting at is that you would need to quote both horizontal
    and vertical fields of view. Using a single value would not be adequate
    as the aspect ratio of the sensors differ. Existing lenses also suffer
    from this problem - people glibly quote a camera as having a "28 - 100mm
    zoom (35mm equivalent)" or whatever, but forget about the aspect ratio....

    Cheers,
    David
    David J Taylor, Jan 28, 2005
    #15
  16. C Wright

    Guest

    In message <>,
    "David J Taylor" <> wrote:

    >What I'm also getting at is that you would need to quote both horizontal
    >and vertical fields of view. Using a single value would not be adequate
    >as the aspect ratio of the sensors differ. Existing lenses also suffer
    >from this problem - people glibly quote a camera as having a "28 - 100mm
    >zoom (35mm equivalent)" or whatever, but forget about the aspect ratio....


    That is also one of the specs.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    , Jan 28, 2005
    #16
  17. wrote:
    > In message <>,
    > "David J Taylor" <> wrote:
    >
    >> What I'm also getting at is that you would need to quote both
    >> horizontal and vertical fields of view. Using a single value would
    >> not be adequate as the aspect ratio of the sensors differ. Existing
    >> lenses also suffer from this problem - people glibly quote a camera
    >> as having a "28 - 100mm zoom (35mm equivalent)" or whatever, but
    >> forget about the aspect ratio....

    >
    > That is also one of the specs.


    The aspect ratio is indeed one of the specs, but you will find that "24
    mm" lenses have different fields of view depending on whether the 24mm
    equivalent was:

    - same horizontal FOV
    - same vertical FOV
    - same diagonal FOV

    Caveat emptor!
    David J Taylor, Jan 29, 2005
    #17
  18. C Wright

    Guest

    In message <>,
    "David J Taylor" <> wrote:

    > wrote:
    >> In message <>,
    >> "David J Taylor" <> wrote:


    >>> What I'm also getting at is that you would need to quote both
    >>> horizontal and vertical fields of view. Using a single value would
    >>> not be adequate as the aspect ratio of the sensors differ. Existing
    >>> lenses also suffer from this problem - people glibly quote a camera
    >>> as having a "28 - 100mm zoom (35mm equivalent)" or whatever, but
    >>> forget about the aspect ratio....


    >> That is also one of the specs.


    >The aspect ratio is indeed one of the specs, but you will find that "24
    >mm" lenses have different fields of view depending on whether the 24mm
    >equivalent was:


    >- same horizontal FOV
    >- same vertical FOV
    >- same diagonal FOV


    .... so you state one or all. The "all" can be derived from other specs.

    Oh, I think I get it now ... you think I'm saying just state one and not
    which one it is?
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    , Jan 29, 2005
    #18
  19. wrote:
    > In message <>,
    > "David J Taylor" <> wrote:
    >
    >> wrote:
    >>> In message <>,
    >>> "David J Taylor" <> wrote:

    >
    >>>> What I'm also getting at is that you would need to quote both
    >>>> horizontal and vertical fields of view. Using a single value would
    >>>> not be adequate as the aspect ratio of the sensors differ.
    >>>> Existing lenses also suffer from this problem - people glibly
    >>>> quote a camera as having a "28 - 100mm zoom (35mm equivalent)" or
    >>>> whatever, but forget about the aspect ratio....

    >
    >>> That is also one of the specs.

    >
    >> The aspect ratio is indeed one of the specs, but you will find that
    >> "24 mm" lenses have different fields of view depending on whether
    >> the 24mm equivalent was:

    >
    >> - same horizontal FOV
    >> - same vertical FOV
    >> - same diagonal FOV

    >
    > ... so you state one or all. The "all" can be derived from other
    > specs.
    >
    > Oh, I think I get it now ... you think I'm saying just state one and
    > not which one it is?


    No, I'm not thinking that is what you're saying.

    What I'm thinking is that if we go the FOV route:

    - you really need to quote all three FOV values (H, V, D) so that fair
    comparisons can be made.

    - quoting aspect ratio as well as FOV only confuses things

    - having to quote so much leaves the 35mm equivalent and therefore leaves
    "focal length multipler" as the most practical way of doing things.

    Where the aspect ratio differs, of course, is between DSLR cameras (3:2)
    and non-SLR cameras (4:3). Quite what the 35mm equivalent means when
    quoted on a 4:3 aspect ratio camera I don't know - is there a standard?

    Cheers,
    David
    David J Taylor, Jan 29, 2005
    #19
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