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Equivalent focal lengths and crop factors... - Photography

Haven't read here for a while. Wondered when all this would surface here. Well, it has and it won't go away, so maybe some clarification is in order. This whole subject is what happens when the tech geeks and the arty types fail to communicate, things get lost in the cracks, important things. We have focal lengths, equivalent focal lengths, angles of view, image area, depth of field, frame composition, perspective... real hodge podge! Two things that weren't considered, and are important, are: 1) The interface between photographer and camera, the view finder. The one thing that does not ever ...

  1. #1

    Default Equivalent focal lengths and crop factors...

    Haven't read here for a while. Wondered when all this would surface
    here. Well, it has and it won't go away, so maybe some clarification is
    in order.

    This whole subject is what happens when the tech geeks and the arty
    types fail to communicate, things get lost in the cracks, important
    things. We have focal lengths, equivalent focal lengths, angles of
    view, image area, depth of field, frame composition, perspective...
    real hodge podge!

    Two things that weren't considered, and are important, are:

    1) The interface between photographer and camera, the view finder.

    The one thing that does not ever change is the natural field of vision
    of an individual, the inherent angle of view. That's the bench mark.
    Now, an individual looks throught the viewfinder of a camera. If it's
    an SLR, the viewfinder presents a perceived angle of view that does not
    change. It does not allow the viewer to perceive the change in the
    lens' angle of view.

    Look through a rangefinder with interchangeable lenses. Different
    marked off fields of view, so the viewer can perceive the changed angle
    of view. Since the viewfinder is not part of the lens' optical train,
    the perceived angle of view *of the viewfinder* does not change, and the
    sense of the differences between the "perspectives" of different focal
    length lenses is not apparent.

    What happens with the SLR is that the eye is fooled into thinking that
    what he/she sees has changed, when it has in fact not changed at all.
    How that happens is obvious: A "standard" lens is one that will present
    to the viewfinder what the eye would see if the viewfinder were a simple
    window, unaltered by an optical train. One can often shoot with both
    eyes open using a standard lens, without suffering the effects of
    difference perceived by each eye.

    Can't do that with a telephoto or wide angle. Well, at least I can't...

    So what is going on here is that the camera user comes to identify the
    perceived effect of different focal lengths, and comes to associate
    particular differences with particular focal length lenses. And this is
    why the persistent popularity of the "equivalent focal length".

    Are the tech geeks right? Yep, they are. Is that important? Yep, it
    is. Why? Because some things don't change, and one of them is DOF.
    Another is relative distortion of the scene image. Both of these are
    very important, of course.

    Which leads to the second thing.

    2) Perspective.

    It turns out that there are two different definitions in common usage.
    Now never mind the dictionaries, we know this without consulting them.
    The first and literal definition is "what you see from where you are".
    Here, we're talking about what you can and cannot see from a point of
    view, which changes when the point of view is changed. You change your
    viewing position, and some things that were not visible become so, and
    some things that were visible, now are not.

    That's not the same as the second definition, which has to do with the
    relative size of viewed objects. The problem here is that this second
    definition can easily be assumed to be a subset of the first: Things
    get larger as one gets closer; given the natural angle of view, moving
    closer makes an object take up more room in the field of vision.

    However, the relative size of objects in the scene can be made
    independent of the point of view created perspective. That is easily
    accomplished with optics (and recorded in camera) by distorting the
    scene optically. Artists do this all the time to achieve the effects
    they want. They call it a change in perspective, and their use of the
    term is what has established the second definition. Artists use
    cameras, and so photography uses both definitions.

    What's the problem? Well, there's a "gotcha!!" lurking here. And that
    is that a photographer expects the camera to record reality as it is,
    because that's what cameras are supposed to do. Right?

    Well, that's as may be, but the reality is that no, they do not. What
    they do is record an optically produced image, whatever that may be, and
    the unwary can really get confused when optical distortion is not
    acknowledged.

    Here's the reality check: If things change in relative size, expect
    different things to be visible. If different things are not visible,
    you're looking at an optically produced distortion. And that's how you
    tell which definition is being used.

    The arty types don't care about all this "semantic detail". Perspective
    change via distortion and perspective change via change in position are
    deemed equivalent for their purposes, or so it seems. Not being an arty
    type I wouldn't know for sure.

    The tech geeks insist that they are entirely different things and should
    never be confused. Perspective change is never produced by a change in
    focal length, so they say, and according to the first definition, they're
    right. And for them, apparently, that's all that matters. Not being a
    tech geek, I wouldn't know for sure.

    The truth is that both are missing an important aspect of this business,
    and that is the effect these changes have on the viewer. Trouble is,
    both types are also viewers, and because of this lack of complete
    understanding, cannot come to an agreement about what's what.

    There are some truths in some of the statements made, of course.

    You cannot change perspective of the first definition by changing focal
    lengths. But it's equally true that you certainly can change
    perspective by the second definition by changing focal lengths. What
    makes both true is that one makes the change by distortion and the other
    does not.

    As a camera user of some experience, you can equate the angle of view
    provided by a focal length in one format with the perceived angle of
    view in another. But the lenses themselves do not change focal length,
    nor do they change angle of view. Enter the crop factor.

    Incidentally, an optical train is an optical train whether displaying a
    recorded image, or recording a displayed image. Optical crop is optical
    crop. No, the two trains are not designed alike, but that's irrelevant.
    For what its worth, that is...

    Maybe if you guys would think all this through, you would realize that
    reality does not change, and that differences in opinion are the result
    of different perceptions. You want to be completely right? Better
    think these things through a bit better. Otherwise, all you guys have
    stuff to learn, and are better off listening to each other and trying to
    figure out what you've missed.

    Myself included, of course. I walk the walk I talk: tell me where I
    ed up here, or what I missed and I'll willingly stand instructed.

    Will D.



    Will D. Guest

  2. #2

    Default Re: Equivalent focal lengths and crop factors...

    "Will D." <willdno.spam> writes:
    > You cannot change perspective of the first definition by changing focal
    > lengths. But it's equally true that you certainly can change
    > perspective by the second definition by changing focal lengths. What
    > makes both true is that one makes the change by distortion and the other
    > does not.
    The change you are making in 'distortion' are not changing the
    perspective. Were this the case, then the objects present in both
    frames would have different 'perspectives' (which they do not). The
    'perspective' here is created by including other objects around the
    edges which were not included in the first frame (or removing them).

    B>
    Bruce Murphy Guest

  3. #3

    Default Re: Equivalent focal lengths and crop factors...

    "A "standard" lens is one that will present
    to the viewfinder what the eye would see if the viewfinder were a simple
    window, unaltered by an optical train."

    I don't believe this was true on a 35mm film as the standard is 50mm when
    approx a 70mm will give 1:1, but with a 1.6 crop with most digitals it may
    now be right !

    "Will D." <willdno.spam> wrote in message
    news:10si5mee4a5k3aacorp.supernews.com...
    > Haven't read here for a while. Wondered when all this would surface
    > here. Well, it has and it won't go away, so maybe some clarification is
    > in order.
    >
    > This whole subject is what happens when the tech geeks and the arty
    > types fail to communicate, things get lost in the cracks, important
    > things. We have focal lengths, equivalent focal lengths, angles of
    > view, image area, depth of field, frame composition, perspective...
    > real hodge podge!
    >
    > Two things that weren't considered, and are important, are:
    >
    > 1) The interface between photographer and camera, the view finder.
    >
    > The one thing that does not ever change is the natural field of vision
    > of an individual, the inherent angle of view. That's the bench mark.
    > Now, an individual looks throught the viewfinder of a camera. If it's
    > an SLR, the viewfinder presents a perceived angle of view that does not
    > change. It does not allow the viewer to perceive the change in the
    > lens' angle of view.
    >
    > Look through a rangefinder with interchangeable lenses. Different
    > marked off fields of view, so the viewer can perceive the changed angle
    > of view. Since the viewfinder is not part of the lens' optical train,
    > the perceived angle of view *of the viewfinder* does not change, and the
    > sense of the differences between the "perspectives" of different focal
    > length lenses is not apparent.
    >
    > What happens with the SLR is that the eye is fooled into thinking that
    > what he/she sees has changed, when it has in fact not changed at all.
    > How that happens is obvious: A "standard" lens is one that will present
    > to the viewfinder what the eye would see if the viewfinder were a simple
    > window, unaltered by an optical train. One can often shoot with both
    > eyes open using a standard lens, without suffering the effects of
    > difference perceived by each eye.
    >
    > Can't do that with a telephoto or wide angle. Well, at least I can't...
    >
    > So what is going on here is that the camera user comes to identify the
    > perceived effect of different focal lengths, and comes to associate
    > particular differences with particular focal length lenses. And this is
    > why the persistent popularity of the "equivalent focal length".
    >
    > Are the tech geeks right? Yep, they are. Is that important? Yep, it
    > is. Why? Because some things don't change, and one of them is DOF.
    > Another is relative distortion of the scene image. Both of these are
    > very important, of course.
    >
    > Which leads to the second thing.
    >
    > 2) Perspective.
    >
    > It turns out that there are two different definitions in common usage.
    > Now never mind the dictionaries, we know this without consulting them.
    > The first and literal definition is "what you see from where you are".
    > Here, we're talking about what you can and cannot see from a point of
    > view, which changes when the point of view is changed. You change your
    > viewing position, and some things that were not visible become so, and
    > some things that were visible, now are not.
    >
    > That's not the same as the second definition, which has to do with the
    > relative size of viewed objects. The problem here is that this second
    > definition can easily be assumed to be a subset of the first: Things
    > get larger as one gets closer; given the natural angle of view, moving
    > closer makes an object take up more room in the field of vision.
    >
    > However, the relative size of objects in the scene can be made
    > independent of the point of view created perspective. That is easily
    > accomplished with optics (and recorded in camera) by distorting the
    > scene optically. Artists do this all the time to achieve the effects
    > they want. They call it a change in perspective, and their use of the
    > term is what has established the second definition. Artists use
    > cameras, and so photography uses both definitions.
    >
    > What's the problem? Well, there's a "gotcha!!" lurking here. And that
    > is that a photographer expects the camera to record reality as it is,
    > because that's what cameras are supposed to do. Right?
    >
    > Well, that's as may be, but the reality is that no, they do not. What
    > they do is record an optically produced image, whatever that may be, and
    > the unwary can really get confused when optical distortion is not
    > acknowledged.
    >
    > Here's the reality check: If things change in relative size, expect
    > different things to be visible. If different things are not visible,
    > you're looking at an optically produced distortion. And that's how you
    > tell which definition is being used.
    >
    > The arty types don't care about all this "semantic detail". Perspective
    > change via distortion and perspective change via change in position are
    > deemed equivalent for their purposes, or so it seems. Not being an arty
    > type I wouldn't know for sure.
    >
    > The tech geeks insist that they are entirely different things and should
    > never be confused. Perspective change is never produced by a change in
    > focal length, so they say, and according to the first definition, they're
    > right. And for them, apparently, that's all that matters. Not being a
    > tech geek, I wouldn't know for sure.
    >
    > The truth is that both are missing an important aspect of this business,
    > and that is the effect these changes have on the viewer. Trouble is,
    > both types are also viewers, and because of this lack of complete
    > understanding, cannot come to an agreement about what's what.
    >
    > There are some truths in some of the statements made, of course.
    >
    > You cannot change perspective of the first definition by changing focal
    > lengths. But it's equally true that you certainly can change
    > perspective by the second definition by changing focal lengths. What
    > makes both true is that one makes the change by distortion and the other
    > does not.
    >
    > As a camera user of some experience, you can equate the angle of view
    > provided by a focal length in one format with the perceived angle of
    > view in another. But the lenses themselves do not change focal length,
    > nor do they change angle of view. Enter the crop factor.
    >
    > Incidentally, an optical train is an optical train whether displaying a
    > recorded image, or recording a displayed image. Optical crop is optical
    > crop. No, the two trains are not designed alike, but that's irrelevant.
    > For what its worth, that is...
    >
    > Maybe if you guys would think all this through, you would realize that
    > reality does not change, and that differences in opinion are the result
    > of different perceptions. You want to be completely right? Better
    > think these things through a bit better. Otherwise, all you guys have
    > stuff to learn, and are better off listening to each other and trying to
    > figure out what you've missed.
    >
    > Myself included, of course. I walk the walk I talk: tell me where I
    > ed up here, or what I missed and I'll willingly stand instructed.
    >
    > Will D.
    >
    >
    >

    dylan Guest

  4. #4

    Default Re: Equivalent focal lengths and crop factors...

    "dylan" <spamnone.com> writes:
    > "A "standard" lens is one that will present
    > to the viewfinder what the eye would see if the viewfinder were a simple
    > window, unaltered by an optical train."
    >
    > I don't believe this was true on a 35mm film as the standard is 50mm when
    > approx a 70mm will give 1:1, but with a 1.6 crop with most digitals it may
    > now be right !
    70mm will give 1:1? How can you possibly make this statement given the
    huge range of viewfinder magnifications available?

    B>
    Bruce Murphy Guest

  5. #5

    Default Re: Equivalent focal lengths and crop factors...

    Let me try to explain.

    If I look through my EOS 3 using a 24-85mm lens and compare the view through
    the viewfinder with the view with my eyes I get the same size image direct
    or through viewfinder when the lens is 70mm. If I try my EOS-10D the setting
    is between 50 and 55mm.

    Looking at the new Nikon F6, as an example, they quote viewfinder
    magnification as .74 with 50mm and the EOS 1Ds Mk2 is .70 at 50mm.

    The diagonal coverage of a 50mm is 40deg and a 70mm is 29deg giving a
    maginification of 1.38.

    1.38 x 0.7 = .96 and 1.38 x .74 = 1.02

    both near enough to 1 for me.

    Obviously as you say if there are other magnifications then this doesn't
    work, ie Minolta 7 is 0.8 at 50mm, but I've always 70mm to be correct for my
    cameras.

    Certainly not the standard 50mm !!

    Cheers



    "Bruce Murphy" <pack-newsrattus.net> wrote in message
    news:m2acs6ws75.fsfgreybat.rattus.net...
    > "dylan" <spamnone.com> writes:
    >
    >> "A "standard" lens is one that will present
    >> to the viewfinder what the eye would see if the viewfinder were a simple
    >> window, unaltered by an optical train."
    >>
    >> I don't believe this was true on a 35mm film as the standard is 50mm when
    >> approx a 70mm will give 1:1, but with a 1.6 crop with most digitals it
    >> may
    >> now be right !
    >
    > 70mm will give 1:1? How can you possibly make this statement given the
    > huge range of viewfinder magnifications available?
    >
    > B>

    dylan Guest

  6. #6

    Default Re: Equivalent focal lengths and crop factors...

    "dylan" <spamnone.com> writes:
    > Let me try to explain.
    >
    > If I look through my EOS 3 using a 24-85mm lens and compare the view through
    > the viewfinder with the view with my eyes I get the same size image direct
    > or through viewfinder when the lens is 70mm. If I try my EOS-10D the setting
    > is between 50 and 55mm.
    >
    > Looking at the new Nikon F6, as an example, they quote viewfinder
    > magnification as .74 with 50mm and the EOS 1Ds Mk2 is .70 at 50mm.
    Not a particularly wide selection. The high-end bodies in both ranges
    tend to have fairly similar eyepiece magnifications.
    > The diagonal coverage of a 50mm is 40deg and a 70mm is 29deg giving a
    > maginification of 1.38.
    >
    > 1.38 x 0.7 = .96 and 1.38 x .74 = 1.02
    >
    > both near enough to 1 for me.
    >
    > Obviously as you say if there are other magnifications then this doesn't
    > work, ie Minolta 7 is 0.8 at 50mm, but I've always 70mm to be correct for my
    > cameras.
    Things vary a bit more with some of the manual focus bodies.
    > Certainly not the standard 50mm !!
    The 'standard' lens is defined in terms of closeness to the diagonal
    of the format in question. With such a lens (actually around 45mm on
    35mm format) coupled with that format, you'll end up with a print
    whose perspective looks natural at a normal viewing distance. In
    contrast, shorter lenses will produce prints whose perspective looks
    odd unless you're closer, and longer ones odd images unless you are
    further away.

    B>
    Bruce Murphy Guest

  7. #7

    Default Re: Equivalent focal lengths and crop factors...

    Will D. <willdno.spam> wrote:
    > You cannot change perspective of the first definition by changing focal
    > lengths. But it's equally true that you certainly can change
    > perspective by the second definition by changing focal lengths. What
    > makes both true is that one makes the change by distortion and the other
    > does not.
    The relative size of objects with distance does not change with focal length.
    You can easily prove this for yourself with the usual experiments.

    Take two pictures from exactly the same point, one with a telephoto and one
    with a wide angle, not moving the camera in between. Crop the wide angle
    shot so that its framing matches the telephoto shot, and you will see that
    they are identical. There is no distortion, and there is no perspective
    change by either of your definitions.

    --
    Jeremy | [email]jeremyexit109.com[/email]
    Jeremy Nixon Guest

  8. #8

    Default Re: Equivalent focal lengths and crop factors...

    In article <cqbg5o$3o8$1newsg4.svr.pol.co.uk>, dylan <spamnone.com> wrote:
    >"A "standard" lens is one that will present
    >to the viewfinder what the eye would see if the viewfinder were a simple
    >window, unaltered by an optical train."
    >
    >I don't believe this was true on a 35mm film as the standard is 50mm when
    >approx a 70mm will give 1:1, but with a 1.6 crop with most digitals it may
    >now be right !
    I guess you grew up with the modern auto-everything cameras, and their tiny
    little viewfinders. Try looking through the viewfinder of an older camera
    some time; something like a Nikon F2, or even just a Pentax Spotmatic.

    Unfortunately when more and more camera automation came along, the makers
    had a problem. They were stuck with three choices: to not present details
    of what the camera was doing in the viewfinder (unacceptable in those days;
    photographers might accept some level of automation, but they knew enough
    not to trust the camera without verification); to present the information
    alongside the traditional viewfinder (expensive, and difficult to use for
    people wearing eyeglasses), or to reduce the size of the viewfinder image
    to free up some space for all the additional display.

    The modern digitals have, quite often, chosen to shrink the usage even
    more (presumably because they share viewfinder optics with a film sibling);
    the D70 still only has a magnification of 0.8 with a 50mm lens. Even the
    D2X only gets a little better, at 0.86X. Canon are slightly better; the
    0.70 of the 1DsII is somewhat understandable because of the larger sensor,
    and the 300D matches the D70 at 0.8x. The 10D and 20D are both close to
    0.9x, which is better than the far more expensive D2!
    But the best viewfinder I've seen in a DSLR is in the Pentax *ist-D/DS.
    These both have viewfinder magnifications of 0.95. Considering the fact
    that the *ist-DS is in the same price bracket as the D70 and 300D, it's
    quite impressive to see a viewfinder that large in a budget(sic) DSLR.

    Disclaimer: I own a *ist-D. But I've used several of the alternatives
    (including a D1, a 10D, and a D100), so I speak from personal experience.
    John Francis Guest

  9. #9

    Default Re: Equivalent focal lengths and crop factors...

    On 2004-12-22, Jeremy Nixon <jeremyexit109.com> wrote:
    > Will D. <willdno.spam> wrote:
    >
    >> You cannot change perspective of the first definition by changing focal
    >> lengths. But it's equally true that you certainly can change
    >> perspective by the second definition by changing focal lengths. What
    >> makes both true is that one makes the change by distortion and the other
    >> does not.
    >
    > The relative size of objects with distance does not change with focal length.
    > You can easily prove this for yourself with the usual experiments.
    >
    > Take two pictures from exactly the same point, one with a telephoto and one
    > with a wide angle, not moving the camera in between. Crop the wide angle
    > shot so that its framing matches the telephoto shot, and you will see that
    > they are identical. There is no distortion, and there is no perspective
    > change by either of your definitions.
    This is true, but you miss the entire point:

    It is the perceived angle of view a) through the viewfinder, and b) when
    viewing a print in the normal manner, that creates this effect.

    The viewfinder enforces a single angle of view, and so does the standard
    print viewing practice. The latter would have you hold the print at
    approximately the distance equal to the diagonal of the print itself.

    If you want to complete the experiment you cite properly, you should
    view the prints at the appropriate distances. For the wide angle shot,
    put your nose on the surface of the print, or thereabouts. For the
    telephoto shot, stand back across the room. In both cases, the
    distortion effect is cancelled. Of course, that might not serve the
    intent of the photographer...

    But you cannot do this with your viewfinder, and so cannot cancel the
    perceived distortion effect at that point in the process.

    Again, think this through to the end, and you'll likely answer your own
    questions.

    Will D.


    Will D. Guest

  10. #10

    Default Re: Equivalent focal lengths and crop factors...

    (repost - server prob.)

    dylan wrote:
    > "A "standard" lens is one that will present
    > to the viewfinder what the eye would see if the viewfinder were a simple
    > window, unaltered by an optical train."
    >
    > I don't believe this was true on a 35mm film as the standard is 50mm when
    > approx a 70mm will give 1:1, but with a 1.6 crop with most digitals it may
    > now be right !
    Think you could not top post and snip away what is not needed?

    The "normal" view with a cropped sensor (1.5) would be about 30 to 35mm, not 70mm.

    Cheers,
    Alan.

    --
    -- r.p.e.35mm user resource: [url]http://www.aliasimages.com/rpe35mmur.htm[/url]
    -- r.p.d.slr-systems: [url]http://www.aliasimages.com/rpdslrsysur.htm[/url]
    -- [SI] gallery & rulz: [url]http://www.pbase.com/shootin[/url]
    -- e-meil: there's no such thing as a FreeLunch.
    Alan Browne Guest

  11. #11

    Default Re: Equivalent focal lengths and crop factors...

    I never said 'normal' (whatever that is) was 70mm with a 1.5 crop. All I
    know is if I look through my EOS-1D with approx 50mm lens the image in the
    viewfinder is the same size to my eye as looking without the camera, 1.5 x
    50mm = 75mm.

    Cheers

    "Alan Browne" <alan.brownefreelunchVideotron.ca> wrote in message
    news:cqcfam$a6j$1inews.gazeta.pl...
    >
    > The "normal" view with a cropped sensor (1.5) would be about 30 to 35mm,
    > not 70mm.
    >
    ..


    dylan Guest

  12. #12

    Default Re: Equivalent focal lengths and crop factors...

    try EOS-10D not 1D, my typo

    "dylan" <spamnone.com> wrote in message
    news:cqcfq4$cti$1newsg3.svr.pol.co.uk...
    >I never said 'normal' (whatever that is) was 70mm with a 1.5 crop. All I
    >know is if I look through my EOS-1D with approx 50mm lens the image in the
    >viewfinder is the same size to my eye as looking without the camera, 1.5 x
    >50mm = 75mm.
    >
    > Cheers

    dylan Guest

  13. #13

    Default Re: Equivalent focal lengths and crop factors...

    Will D. <willdno.spam> wrote:
    > If you want to complete the experiment you cite properly, you should
    > view the prints at the appropriate distances. For the wide angle shot,
    > put your nose on the surface of the print, or thereabouts. For the
    > telephoto shot, stand back across the room. In both cases, the
    > distortion effect is cancelled. Of course, that might not serve the
    > intent of the photographer...
    Except that the wide-angle shot, once cropped, *becomes* a telephoto
    shot. Cropping it is, for the purpose of the experiment, the same thing
    as using a longer focal length -- this is the conclusion of the
    experiment, not the premise, but in the end, zooming in is just a way
    to optically crop the image.

    The relative sizes of objects according to distance is a function of
    the distances involved -- the lens can't change them, unless it's
    distorting them due to optical defects, which doesn't really count.

    When you look through a long telephoto lens, it may look like the
    distances are compressed, but that is an illusion coming from the fact
    that you are seeing the scene in a way your unaided eye cannot. The
    perspective is actually identical to what you see with any focal length.

    --
    Jeremy | [email]jeremyexit109.com[/email]
    Jeremy Nixon Guest

  14. #14

    Default Re: Equivalent focal lengths and crop factors...

    On 2004-12-23, Jeremy Nixon <jeremyexit109.com> wrote:
    > Will D. <willdno.spam> wrote:
    >
    >> If you want to complete the experiment you cite properly, you should
    >> view the prints at the appropriate distances. For the wide angle shot,
    >> put your nose on the surface of the print, or thereabouts. For the
    >> telephoto shot, stand back across the room. In both cases, the
    >> distortion effect is cancelled. Of course, that might not serve the
    >> intent of the photographer...
    >
    > Except that the wide-angle shot, once cropped, *becomes* a telephoto
    > shot. Cropping it is, for the purpose of the experiment, the same thing
    > as using a longer focal length -- this is the conclusion of the
    > experiment, not the premise, but in the end, zooming in is just a way
    > to optically crop the image.
    Well, if the point you are making is that photographic optical trains do
    not introduce gratuitous distortion, you are correct, AFAIK. But that
    does not address the issue I raised.
    > The relative sizes of objects according to distance is a function of
    > the distances involved -- the lens can't change them, unless it's
    > distorting them due to optical defects, which doesn't really count.
    Yes, we can assume no gratuitous distortions, I think.
    > When you look through a long telephoto lens, it may look like the
    > distances are compressed, but that is an illusion coming from the fact
    > that you are seeing the scene in a way your unaided eye cannot. The
    > perspective is actually identical to what you see with any focal length.
    An illusion is an apparency that is the function of the interpretive
    mind, which is classically dispelled by blinking one's eyes and taking
    another look. Big noses and tiny ears in portraits taken with wide
    angle lenses cannot be dispelled by blinking one's eyes. Compared to
    what one sees with unaided vision, they constitute distortions.

    I defined the second usage of the term "perspective" as caused by
    distortion, because we are accustomed to gauging our position in our
    environment, in part, by the relative size of the objects around us.
    You can make the case that this second definition is an illusory
    corollary of the first, but the fact is that artists have long used this
    second definition and thus it is customary usage in photography.

    Will D.

    Will D. Guest

  15. #15

    Default Re: Equivalent focal lengths and crop factors...

    Will D. <willdno.spam> wrote:
    > An illusion is an apparency that is the function of the interpretive
    > mind, which is classically dispelled by blinking one's eyes and taking
    > another look. Big noses and tiny ears in portraits taken with wide
    > angle lenses cannot be dispelled by blinking one's eyes. Compared to
    > what one sees with unaided vision, they constitute distortions.
    But they are not a product of focal length, nor is the amount of such
    visual distortion a function of focal length. It is not the wide-angle
    lens that causes this.

    --
    Jeremy | [email]jeremyexit109.com[/email]
    Jeremy Nixon Guest

  16. #16

    Default Re: Equivalent focal lengths and crop factors...

    On 2004-12-23, Jeremy Nixon <jeremyexit109.com> wrote:
    > Will D. <willdno.spam> wrote:
    >
    >> An illusion is an apparency that is the function of the interpretive
    >> mind, which is classically dispelled by blinking one's eyes and taking
    >> another look. Big noses and tiny ears in portraits taken with wide
    >> angle lenses cannot be dispelled by blinking one's eyes. Compared to
    >> what one sees with unaided vision, they constitute distortions.
    >
    > But they are not a product of focal length, nor is the amount of such
    > visual distortion a function of focal length. It is not the wide-angle
    > lens that causes this.
    Would you please explain this phenomena, then? Perhaps we all might
    learn something here.

    Will D.

    Will D. Guest

  17. #17

    Default Re: Equivalent focal lengths and crop factors...

    Will D. wrote:
    > On 2004-12-23, Jeremy Nixon <jeremyexit109.com> wrote:
    >> Will D. <willdno.spam> wrote:
    >>
    >>> An illusion is an apparency that is the function of the interpretive
    >>> mind, which is classically dispelled by blinking one's eyes and
    >>> taking another look. Big noses and tiny ears in portraits taken
    >>> with wide angle lenses cannot be dispelled by blinking one's eyes.
    >>> Compared to what one sees with unaided vision, they constitute
    >>> distortions.
    >>
    >> But they are not a product of focal length, nor is the amount of such
    >> visual distortion a function of focal length. It is not the
    >> wide-angle lens that causes this.
    >
    > Would you please explain this phenomena, then? Perhaps we all might
    > learn something here.
    >
    > Will D.
    Seems to me it has been esplained, discussed, and demonstrated to within
    an inch of its (apparently eternal) life.

    And without malice or meanness, just so at least one of us learns
    something, it's "this phenomenon", "these phenomena".

    Merry Christmas.


    --
    Frank ess


    Frank ess Guest

  18. #18

    Default Re: Equivalent focal lengths and crop factors...

    Will D. <willdno.spam> wrote:

    [so-called wide-angle distortion]
    >> But they are not a product of focal length, nor is the amount of such
    >> visual distortion a function of focal length. It is not the wide-angle
    >> lens that causes this.
    >
    > Would you please explain this phenomena, then? Perhaps we all might
    > learn something here.
    I'm not sure how many different ways it can be explained before a few
    people stop refusing to believe it.

    It is a product of the camera position relative to the subject.

    Some people *think* is has to do with the lens focal length because,
    when using a wide angle lens, you get closer to the subject in order to
    get the framing you want. But it is getting closer that does it. If
    it had to do with focal length, you would get big noses and all that
    stuff shooting a full-length picture of someone from 15 feet away with
    a point and shoot digicam, since the lens would be less than 10mm.
    But you don't, because it doesn't.

    --
    Jeremy | [email]jeremyexit109.com[/email]
    Jeremy Nixon Guest

  19. #19

    Default Re: Equivalent focal lengths and crop factors...

    "Frank ess" <frankfshe2fs.com> wrote in message
    news:a4GdnVFALqAd6FHcRVn-tAgiganews.com...
    <snip>
    > Seems to me it has been esplained, discussed, and demonstrated to within
    > an inch of its (apparently eternal) life.
    > And without malice or meanness, just so at least one of us learns
    > something, it's "this phenomenon", "these phenomena".
    >
    > Merry Christmas.
    > --
    > Frank ess
    -----------
    Also, the word is spelled "explained" not "esplained". We all make errors
    from time to time, don't we?
    Merry Christmas to you and your family.
    Don F


    Don F Guest

  20. #20

    Default Re: Equivalent focal lengths and crop factors...

    Don F wrote:
    > "Frank ess" <frankfshe2fs.com> wrote in message
    > news:a4GdnVFALqAd6FHcRVn-tAgiganews.com...
    > <snip>
    >> Seems to me it has been esplained, discussed, and demonstrated to
    >> within an inch of its (apparently eternal) life.
    >> And without malice or meanness, just so at least one of us learns
    >> something, it's "this phenomenon", "these phenomena".
    >>
    >> Merry Christmas.
    >> --
    >> Frank ess
    > -----------
    > Also, the word is spelled "explained" not "esplained". We all make
    > errors from time to time, don't we?
    > Merry Christmas to you and your family.
    > Don F
    Well, YOU can esplain that to Ricky and Lucy. Dipsh*t picayune spelling
    cop. How do you feel now?

    Merry Christms to you. (Big smiley face)

    --
    --
    Frank ess


    Frank ess Guest

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