Should 4/3 lenses be half the size of full frame lenses?

Discussion in 'Digital Photography' started by bob, Jun 13, 2011.

  1. bob

    bob Guest

    4/3 camera has a sensor that is about half the length and height of a full
    frame sensor (1/4 the area).

    Does that mean a 4/3 camera lense would be half the diameter of an
    equivalent full frame lense?
     
    bob, Jun 13, 2011
    #1
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  2. "bob" <> wrote in message
    news:it5bhf$djb$...
    > 4/3 camera has a sensor that is about half the length and height of a
    > full frame sensor (1/4 the area).
    >
    > Does that mean a 4/3 camera lense would be half the diameter of an
    > equivalent full frame lense?


    ... and half the length, and one eighth of the weight! Doesn't seem to be
    so in practice, though. You also use the word "equivalent". To be
    equivalent in light gathering power an f/2.8 full-frame lens would need to
    be replaced by an f/1.4 half-frame lens. Somewhat more costly to make, if
    possible at all.

    Cheers,
    David
     
    David J Taylor, Jun 13, 2011
    #2
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  3. "David Dyer-Bennet" <> wrote in message
    news:...
    []
    > We've been around on this before, haven't we? It sounds familiar.


    Yes, perhaps the OP might like to consult the archives.

    > Because it's scaled by the focal length, the f number means the
    > same thing for any format, *In terms of exposure*. A micro 4/3
    > f/2.8 lens is exactly equivalent to a full-frame f/2.8 lens *in that
    > regard*.
    > When I mount my Nikon 50/1.8 (via an adapter) to my
    > Micro 4/3 camera, the marked f numbers on the lens aperture
    > ring remain correct.
    >
    > So I'm not sure what you mean by "light gathering power".
    >
    > That's the equivalence most people care about when discussing
    > this issue, but of course it's not the only one. I vaguely remember
    > that you insist on f/1.4 to be able to get equally shallow
    > depth of field, or something? (Unless I'm confusing you with
    > somebody else, in which case my apologies to both you and
    > the unknown other person.) I haven't chased through the details
    > myself, but I have no reason to doubt you.
    >
    > Still, flatly telling people that f/1.4 on a micro 4/3rds lens is
    > equivalent to f/2.8 on a full-frame lens is just plain wrong.


    Which is why I asked the OP to clarify what they meant by "equivalent".
    For the same number of photons on the sensor, what I say is correct.

    I haven't done the depth of field sums - that was likely Roger Clarkson.

    Cheers,
    David
     
    David J Taylor, Jun 13, 2011
    #3
  4. "Bruce" <> wrote in message
    news:...
    []
    > You're showing your (profound) ignorance again, David.
    >
    > The light gathering power of an f/2.8 Four Thirds lens is identical to
    > an f/2.8 APS-C lens, an f/2.8 full frame lens and an f/2.8 medium
    > format lens, regardless of focal length.
    >
    > The clue is in the term "f/".
    >
    > Perhaps you should stick to enjoying your consumer grade DSLR and your
    > consumer grade lenses, and stop dispensing consumer grade "advice".


    Lenses with the same f/number (more strictly, T/number) will deliver the
    same number of photons per unit area, but as the full-frame sensor has
    four times the sensitive area of the half-frame sensor, it gathers four
    times as much light - four times as many photons. To get the same number
    of photons, you need a lens with twice the physical opening, four times
    the aperture area, and one half the numeric f/number.

    It's why small sensor cameras need a higher light level to get the same
    signal-to-noise ratio or, put another way, why they are noisier at higher
    ISOs. Their smaller sensor captures fewer photons for a given f/number
    and light level.
     
    David J Taylor, Jun 13, 2011
    #4
  5. On Jun 13, 1:40 pm, "David J Taylor" <david-
    > wrote:
    > "Bruce" <> wrote in message
    >
    > news:...
    > []
    >
    > > You're showing your (profound) ignorance again, David.

    >
    > > The light gathering power of an f/2.8 Four Thirds lens is identical to
    > > an f/2.8 APS-C lens, an f/2.8 full frame lens and an f/2.8 medium
    > > format lens, regardless of focal length.

    >
    > > The clue is in the term "f/".

    >
    > > Perhaps you should stick to enjoying your consumer grade DSLR and your
    > > consumer grade lenses, and stop dispensing consumer grade "advice".

    >
    > Lenses with the same f/number (more strictly, T/number) will deliver the
    > same number of photons per unit area, but as the full-frame sensor has
    > four times the sensitive area of the half-frame sensor, it gathers four
    > times as much light - four times as many photons.  To get the same number
    > of photons, you need a lens with twice the physical opening, four times
    > the aperture area, and one half the numeric f/number.


    You're assuming the same pixel count, which is regrettably frequently
    true, but is not an inherent aspect of sensor size. I think a lot of
    the
    confusion arises from your relating the issue to sensor size
    rather than pixel size (okay, sensel size).

    Same number of photos per unit area is what matters for exposure.
    "Everybody knows" this and it's true, as true as anything is anyway.
    Your statements always start out looking like they're trying to
    deny this, which gets everybody up in arms, because this really
    *is* true.

    > It's why small sensor cameras need a higher light level to get the same
    > signal-to-noise ratio or, put another way, why they are noisier at higher
    > ISOs.  Their smaller sensor captures fewer photons for a given f/number
    > and light level.


    Hmmm; this feels like a back-door way of coming at the problem, and
    also
    doesn't give me any help in minimzing noise -- both my cameras have
    a base ISO of 200, so I can't turn down the ISO in either case.

    But one of them is a Nikon D700, and one is an Olympus E-PL2. I know
    which one is noisier at high ISO! It's the one with the smaller
    pixels,
    which in this case is the one with the smaller sensor. (They're also
    the
    same number of pixels, so that makes all sorts of comparisons easy.)

    Signal-to-noise ratio isn't a stated spec or anything we have a
    standard
    for measuring in cameras (that's widely used and understood, anyway).

    It's generally true that, for any given technology, smaller pixels
    will be
    noisier at ANY ISO (than larger pixels at that same ISO). Won't
    argue
    against that for a moment.

    But despite having been around this course before, I still wasn't
    able to read that out of your initial statements. It'd maybe be good
    to work on how you present this issue, to avoid the initial confusion
    and opposition.
     
    David Dyer-Bennet, Jun 13, 2011
    #5
  6. "David Dyer-Bennet" <> wrote in message
    news:...
    []
    > You're assuming the same pixel count, which is regrettably frequently
    > true, but is not an inherent aspect of sensor size. I think a lot of
    > the
    > confusion arises from your relating the issue to sensor size
    > rather than pixel size (okay, sensel size).


    Pixel count actually has nothing to do with it. It's the sensor area
    which matters. Pixel count sets how you trade-off spatial resolution for
    signal-to-noise ratio at the pixel level.

    > Same number of photos per unit area is what matters for exposure.
    > "Everybody knows" this and it's true, as true as anything is anyway.
    > Your statements always start out looking like they're trying to
    > deny this, which gets everybody up in arms, because this really
    > *is* true.


    Yes, it is true.

    > Hmmm; this feels like a back-door way of coming at the problem, and
    > also
    > doesn't give me any help in minimzing noise -- both my cameras have
    > a base ISO of 200, so I can't turn down the ISO in either case.


    More sensitive area reduces noise at the same ISO when more photons are
    captured, other things being equal.

    > But one of them is a Nikon D700, and one is an Olympus E-PL2. I know
    > which one is noisier at high ISO! It's the one with the smaller
    > pixels,
    > which in this case is the one with the smaller sensor. (They're also
    > the
    > same number of pixels, so that makes all sorts of comparisons easy.)
    >
    > Signal-to-noise ratio isn't a stated spec or anything we have a
    > standard
    > for measuring in cameras (that's widely used and understood, anyway).
    >
    > It's generally true that, for any given technology, smaller pixels
    > will be
    > noisier at ANY ISO (than larger pixels at that same ISO). Won't
    > argue
    > against that for a moment.


    But a newer 4/3 sensor, one with higher quantum efficiency, might just
    beat an older APS-C sensor. That's when all things /aren't/ equal.

    > But despite having been around this course before, I still wasn't
    > able to read that out of your initial statements. It'd maybe be good
    > to work on how you present this issue, to avoid the initial confusion
    > and opposition.


    It takes time to think about these issues, as they are not initially
    obvious.

    Cheers,
    David
     
    David J Taylor, Jun 14, 2011
    #6
  7. bob

    bob Guest

    To me, an 4/3 lense that is equivalent to a 35mm lense should have the same
    maximum f number and angle of view.

    This way, a 35mm camera and a 4/3 camera can shoot the same scene using the
    same exposure (shutter speed and aperture) and end up with more or less
    identical photos (except DOF, noise, and maybe resolution).
     
    bob, Jun 14, 2011
    #7
  8. "bob" <> wrote in message
    news:it71ko$hl7$...
    > To me, an 4/3 lense that is equivalent to a 35mm lense should have the
    > same maximum f number and angle of view.
    >
    > This way, a 35mm camera and a 4/3 camera can shoot the same scene using
    > the same exposure (shutter speed and aperture) and end up with more or
    > less identical photos (except DOF, noise, and maybe resolution).


    Yes, that's a perfectly fair way of looking at it - depending on your
    definition of "identical"! Given that, why aren't the lenses half the
    linear dimension, a quarter of the area, and an eighth of the weight,
    particularly for micro-4/3 where back-focus requirements are less?

    Cheers,
    David
     
    David J Taylor, Jun 14, 2011
    #8
  9. bob

    Bruce Guest

    Paul Furman <> wrote:
    >Bruce wrote:
    >> The light gathering power of an f/2.8 Four Thirds lens is identical to
    >> an f/2.8 ...full frame lens

    >
    >With 1/4 the sensor size so 1/4 the print size.



    That's only true if the Four Thirds sensor has a quarter as many
    pixels as the full frame sensor.

    If the number of pixels is the same, the print size will be the same
    for the same ppi at the printing stage. All that matters at the
    printing stage is the number of pixels. The printer has no idea
    whether those pixels came from a P&S, Four Thirds, APS-C, full frame
    or medium format.
     
    Bruce, Jun 14, 2011
    #9
  10. bob

    nospam Guest

    In article <>, Neil
    Harrington <> wrote:

    > >> 4/3 camera has a sensor that is about half the length and height of a
    > >> full frame sensor (1/4 the area).
    > >>
    > >> Does that mean a 4/3 camera lense would be half the diameter of an
    > >> equivalent full frame lense?

    > >
    > > .. and half the length, and one eighth of the weight! Doesn't seem
    > > to be so in practice, though. You also use the word "equivalent". To be
    > > equivalent in light gathering power an f/2.8 full-frame lens
    > > would need to be replaced by an f/1.4 half-frame lens. Somewhat more
    > > costly to make, if possible at all.

    >
    > That makes no sense whatever.


    yes it does.

    > An f/2.8 lens is an f/2.8 lens, regardless of what format it's meant to
    > cover. Its "light gathering power" is the same as any other lens of similar
    > f-number as far as photographic purposes are concerned, disregarding
    > differences in coating, etc.


    it's light gathering power per unit area is the same (exposure) but a
    larger sensor has a larger area so the total amount of light collected
    is higher.

    > Even if you were right about that light-gathering business you'd be wrong in
    > your conclusion: a half-frame format does not have half the diagonal of full
    > frame. (It's 30mm vs about 43mm.)


    4/3rds is approximately 1/4 the area of full frame, or two stops, thus
    an f/2.8 lens on full frame is equivalent to an f/1.4 lens on 4/3rds.
     
    nospam, Jun 14, 2011
    #10
  11. bob

    nospam Guest

    In article <>, Neil
    Harrington <> wrote:

    > > Lenses with the same f/number (more strictly, T/number) will deliver
    > > the same number of photons per unit area,

    >
    > Which is all that matters, so you could stop right there.


    for exposure yes, for total light no.

    > > It's why small sensor cameras need a higher light level to get the
    > > same signal-to-noise ratio or, put another way, why they are noisier
    > > at higher ISOs. Their smaller sensor captures fewer photons for a
    > > given f/number and light level.

    >
    > Regardless of format size, *per unit area* the sensor captures the same
    > number of photons at the same f-number.


    but the area is bigger, so the total is higher.
     
    nospam, Jun 14, 2011
    #11
  12. bob

    nospam Guest

    In article <>, Neil
    Harrington <> wrote:

    > >> An f/2.8 lens is an f/2.8 lens, regardless of what format it's meant
    > >> to cover. Its "light gathering power" is the same as any other lens
    > >> of similar f-number as far as photographic purposes are concerned,
    > >> disregarding differences in coating, etc.

    > >
    > > it's light gathering power per unit area is the same (exposure)

    >
    > Yes. Stop right there.


    no

    > > but a
    > > larger sensor has a larger area so the total amount of light collected
    > > is higher.

    >
    > You didn't stop where I told you.


    that's because there's more to say.

    > Larger sensor = larger area = more light
    > collected = *same exposure*, no difference as long as the f-number is the
    > same.


    however, more light means better signal/noise ratio.

    if you match the noise to obtain the *same* image quality (by raising
    the iso) you can use smaller f/stops on the larger sensor. that's where
    the difference is.

    a good explanation is here:
    <http://clarkvision.com/imagedetail/f-ratio_myth/index.html>

    > >> Even if you were right about that light-gathering business you'd be
    > >> wrong in your conclusion: a half-frame format does not have half the
    > >> diagonal of full frame. (It's 30mm vs about 43mm.)

    > >
    > > 4/3rds is approximately 1/4 the area of full frame,

    >
    > Yep.
    >
    > > or two stops,

    >
    > *Whoa!* where do you get the "or two stops" business?


    1/4 the area is 1/4 the light.

    one stop is half the light and two stops is 1/4. therefore, a sensor
    that has 1/4 the area is a two stop difference.
     
    nospam, Jun 14, 2011
    #12
  13. bob

    dj_nme Guest

    On 15/06/2011 6:26 AM, nospam wrote:
    > In article<>, Neil
    > Harrington<> wrote:
    >
    >>> Lenses with the same f/number (more strictly, T/number) will deliver
    >>> the same number of photons per unit area,

    >>
    >> Which is all that matters, so you could stop right there.

    >
    > for exposure yes, for total light no.


    You really should have stopped with "For exposure, yes."
    That is "total light" as far as taking photographs is concerned.

    >>> It's why small sensor cameras need a higher light level to get the
    >>> same signal-to-noise ratio or, put another way, why they are noisier
    >>> at higher ISOs. Their smaller sensor captures fewer photons for a
    >>> given f/number and light level.

    >>
    >> Regardless of format size, *per unit area* the sensor captures the same
    >> number of photons at the same f-number.

    >
    > but the area is bigger, so the total is higher.


    So what?
    The same f-stop setting gives the same exposure at the same shutter
    speed regardless of format size.

    You seem to have not grasped the reason why some people use the term
    "equivalent f-stop" when taking 4/3, APS and FF.

    Using FF as the baseline, all the others have greater Depth of Field
    (DoF) with lenses of the same angle of view (IE: 35mm Equivalent Focal
    Length [35mm EFL]) with the same f-stop setting.
    "equivalent f-stop" is using a aperture (f-stop) setting that gives an
    equivalent DoF to 35mm at their 35mm EFL, not the same exposure value at
    the same shutter speed.
    To get the same DoF on a 4/3 as a FF the f-stop setting must be twice
    the size (two f-stops); IE: set the 4/3 to f/1.4 @ 25mm FL (50mm in 35mm
    EFL) to get the same Dof as FF set to f/2.8 @ 50mm FL.
    For the same DoF on APS as FF the f-stop setting must be 50 percent
    bigger (one f-stop); IE: set the APS to f/2.0 @ 35mm FL (50mm in 35mm
    EFL) to get the same Dof as FF set to f/2.8 @ 50mm FL.
    It gives a much greater exposure setting at the same shutter setting:
    the shutter speed must be set higher (shorter time) to compensate for
    more light let in by the wider (lower f-stop setting) aperture.
     
    dj_nme, Jun 14, 2011
    #13
  14. bob

    dj_nme Guest

    On 15/06/2011 6:02 AM, Neil Harrington wrote:
    > David J Taylor wrote:
    >> "bob"<> wrote in message
    >> news:it5bhf$djb$...
    >>> 4/3 camera has a sensor that is about half the length and height of a
    >>> full frame sensor (1/4 the area).
    >>>
    >>> Does that mean a 4/3 camera lense would be half the diameter of an
    >>> equivalent full frame lense?

    >>
    >> .. and half the length, and one eighth of the weight! Doesn't seem
    >> to be so in practice, though. You also use the word "equivalent". To be
    >> equivalent in light gathering power an f/2.8 full-frame lens
    >> would need to be replaced by an f/1.4 half-frame lens. Somewhat more
    >> costly to make, if possible at all.

    >
    > That makes no sense whatever.
    >
    > An f/2.8 lens is an f/2.8 lens, regardless of what format it's meant to
    > cover. Its "light gathering power" is the same as any other lens of similar
    > f-number as far as photographic purposes are concerned, disregarding
    > differences in coating, etc.


    Of course it makes no sense: it is dead wrong.
    If "bob" wrote that for the same 35mm equivalent FL that he was after
    the same DoF, then two stops wider aperture (for 4/3, in this case) will
    get the same DoF as FF (35mm full frame) at the same angle of view lens
    (35mm equiv focal length).
    It does not work for exposure, only DoF.

    > Even if you were right about that light-gathering business you'd be wrong in
    > your conclusion: a half-frame format does not have half the diagonal of full
    > frame. (It's 30mm vs about 43mm.)


    In this case (for 4/3), it is really a quarter-frame format (about 22mm
    Vs about 43mm diagonal).
    Not that I really believe that the facts will "get in the way" of "bob"s
    argument.
     
    dj_nme, Jun 14, 2011
    #14
  15. bob

    nospam Guest

    In article <4df7e1cf$0$13395$>, dj_nme
    <> wrote:

    > >>> Lenses with the same f/number (more strictly, T/number) will deliver
    > >>> the same number of photons per unit area,
    > >>
    > >> Which is all that matters, so you could stop right there.

    > >
    > > for exposure yes, for total light no.

    >
    > You really should have stopped with "For exposure, yes."
    > That is "total light" as far as taking photographs is concerned.


    nope. exposure is light per unit area. if you have more area (a larger
    sensor), you have more total light distributed over the larger area,
    which ends up being the same for a given area.

    > >>> It's why small sensor cameras need a higher light level to get the
    > >>> same signal-to-noise ratio or, put another way, why they are noisier
    > >>> at higher ISOs. Their smaller sensor captures fewer photons for a
    > >>> given f/number and light level.
    > >>
    > >> Regardless of format size, *per unit area* the sensor captures the same
    > >> number of photons at the same f-number.

    > >
    > > but the area is bigger, so the total is higher.

    >
    > So what?
    > The same f-stop setting gives the same exposure at the same shutter
    > speed regardless of format size.


    but not the same result. the noise and depth of field are different.

    > You seem to have not grasped the reason why some people use the term
    > "equivalent f-stop" when taking 4/3, APS and FF.


    actually you haven't grasped it, since you contradict yourself below.

    > Using FF as the baseline, all the others have greater Depth of Field
    > (DoF) with lenses of the same angle of view (IE: 35mm Equivalent Focal
    > Length [35mm EFL]) with the same f-stop setting.


    true, but smaller formats will have more noise (all other things being
    equal) so you don't get the same image.

    <http://clarkvision.com/imagedetail/dof_myth/index.html>

    > "equivalent f-stop" is using a aperture (f-stop) setting that gives an
    > equivalent DoF to 35mm at their 35mm EFL, not the same exposure value at
    > the same shutter speed.


    right, which for 4/3rds, is 2 stops wider.

    > To get the same DoF on a 4/3 as a FF the f-stop setting must be twice
    > the size (two f-stops); IE: set the 4/3 to f/1.4 @ 25mm FL (50mm in 35mm
    > EFL) to get the same Dof as FF set to f/2.8 @ 50mm FL.
    > For the same DoF on APS as FF the f-stop setting must be 50 percent
    > bigger (one f-stop); IE: set the APS to f/2.0 @ 35mm FL (50mm in 35mm
    > EFL) to get the same Dof as FF set to f/2.8 @ 50mm FL.
    > It gives a much greater exposure setting at the same shutter setting:
    > the shutter speed must be set higher (shorter time) to compensate for
    > more light let in by the wider (lower f-stop setting) aperture.


    you can also raise the iso, which has the effect of an equivalent s/n
    ratio, and then you can use the same shutter speed with the equivalent
    f/stop.

    that contradicts what you said earlier.
     
    nospam, Jun 14, 2011
    #15
  16. bob

    nospam Guest

    In article <4df7e435$0$13395$>, dj_nme
    <> wrote:

    > >>> 4/3 camera has a sensor that is about half the length and height of a
    > >>> full frame sensor (1/4 the area).
    > >>>
    > >>> Does that mean a 4/3 camera lense would be half the diameter of an
    > >>> equivalent full frame lense?
    > >>
    > >> .. and half the length, and one eighth of the weight! Doesn't seem
    > >> to be so in practice, though. You also use the word "equivalent". To be
    > >> equivalent in light gathering power an f/2.8 full-frame lens
    > >> would need to be replaced by an f/1.4 half-frame lens. Somewhat more
    > >> costly to make, if possible at all.

    > >
    > > That makes no sense whatever.
    > >
    > > An f/2.8 lens is an f/2.8 lens, regardless of what format it's meant to
    > > cover. Its "light gathering power" is the same as any other lens of similar
    > > f-number as far as photographic purposes are concerned, disregarding
    > > differences in coating, etc.

    >
    > Of course it makes no sense: it is dead wrong.


    nope

    > If "bob" wrote that for the same 35mm equivalent FL that he was after
    > the same DoF, then two stops wider aperture (for 4/3, in this case) will
    > get the same DoF as FF (35mm full frame) at the same angle of view lens
    > (35mm equiv focal length).
    > It does not work for exposure, only DoF.


    then it's not equivalent, is it?

    > > Even if you were right about that light-gathering business you'd be wrong in
    > > your conclusion: a half-frame format does not have half the diagonal of full
    > > frame. (It's 30mm vs about 43mm.)

    >
    > In this case (for 4/3), it is really a quarter-frame format (about 22mm
    > Vs about 43mm diagonal).
    > Not that I really believe that the facts will "get in the way" of "bob"s
    > argument.


    they do for you though.
     
    nospam, Jun 14, 2011
    #16
  17. bob

    dj_nme Guest

    On 15/06/2011 8:45 AM, nospam wrote:
    > In article<4df7e1cf$0$13395$>, dj_nme
    > <> wrote:
    >
    >>>>> Lenses with the same f/number (more strictly, T/number) will deliver
    >>>>> the same number of photons per unit area,
    >>>>
    >>>> Which is all that matters, so you could stop right there.
    >>>
    >>> for exposure yes, for total light no.

    >>
    >> You really should have stopped with "For exposure, yes."
    >> That is "total light" as far as taking photographs is concerned.

    >
    > nope. exposure is light per unit area. if you have more area (a larger
    > sensor), you have more total light distributed over the larger area,
    > which ends up being the same for a given area.
    >
    >>>>> It's why small sensor cameras need a higher light level to get the
    >>>>> same signal-to-noise ratio or, put another way, why they are noisier
    >>>>> at higher ISOs. Their smaller sensor captures fewer photons for a
    >>>>> given f/number and light level.
    >>>>
    >>>> Regardless of format size, *per unit area* the sensor captures the same
    >>>> number of photons at the same f-number.
    >>>
    >>> but the area is bigger, so the total is higher.

    >>
    >> So what?
    >> The same f-stop setting gives the same exposure at the same shutter
    >> speed regardless of format size.

    >
    > but not the same result. the noise and depth of field are different.


    You obviously didn't read what I wrote about "equivalent f-stop".
    Are you being deliberately obtuse?

    >> You seem to have not grasped the reason why some people use the term
    >> "equivalent f-stop" when taking 4/3, APS and FF.

    >
    > actually you haven't grasped it, since you contradict yourself below.


    No, I don't.
    It is all about the same Dof and NOT about the same exposure settings.
    Read what I wrote, not what you want to see.

    >> Using FF as the baseline, all the others have greater Depth of Field
    >> (DoF) with lenses of the same angle of view (IE: 35mm Equivalent Focal
    >> Length [35mm EFL]) with the same f-stop setting.

    >
    > true, but smaller formats will have more noise (all other things being
    > equal) so you don't get the same image.
    >
    > <http://clarkvision.com/imagedetail/dof_myth/index.html>


    This is relevant, how?

    >> "equivalent f-stop" is using a aperture (f-stop) setting that gives an
    >> equivalent DoF to 35mm at their 35mm EFL, not the same exposure value at
    >> the same shutter speed.

    >
    > right, which for 4/3rds, is 2 stops wider.


    For the same DoF, not exposure value.

    >> To get the same DoF on a 4/3 as a FF the f-stop setting must be twice
    >> the size (two f-stops); IE: set the 4/3 to f/1.4 @ 25mm FL (50mm in 35mm
    >> EFL) to get the same Dof as FF set to f/2.8 @ 50mm FL.
    >> For the same DoF on APS as FF the f-stop setting must be 50 percent
    >> bigger (one f-stop); IE: set the APS to f/2.0 @ 35mm FL (50mm in 35mm
    >> EFL) to get the same Dof as FF set to f/2.8 @ 50mm FL.
    >> It gives a much greater exposure setting at the same shutter setting:
    >> the shutter speed must be set higher (shorter time) to compensate for
    >> more light let in by the wider (lower f-stop setting) aperture.

    >
    > you can also raise the iso, which has the effect of an equivalent s/n
    > ratio, and then you can use the same shutter speed with the equivalent
    > f/stop.


    No, that would give an over-exposed image.
    Wider aperture requires a shorter exposure time or lower ISO setting for
    the same exposure value.

    Are you sure that you even know which end of a camera to hold?
    I am beginning to doubt this, based on what you've written.

    > that contradicts what you said earlier.


    No, it does not.
    I said nothing about raising ISO settings.
    you have created that from your own imagination.
     
    dj_nme, Jun 15, 2011
    #17
  18. bob

    dj_nme Guest

    On 15/06/2011 8:48 AM, nospam wrote:
    > In article<4df7e435$0$13395$>, dj_nme
    > <> wrote:
    >
    >>>>> 4/3 camera has a sensor that is about half the length and height of a
    >>>>> full frame sensor (1/4 the area).
    >>>>>
    >>>>> Does that mean a 4/3 camera lense would be half the diameter of an
    >>>>> equivalent full frame lense?
    >>>>
    >>>> .. and half the length, and one eighth of the weight! Doesn't seem
    >>>> to be so in practice, though. You also use the word "equivalent". To be
    >>>> equivalent in light gathering power an f/2.8 full-frame lens
    >>>> would need to be replaced by an f/1.4 half-frame lens. Somewhat more
    >>>> costly to make, if possible at all.
    >>>
    >>> That makes no sense whatever.
    >>>
    >>> An f/2.8 lens is an f/2.8 lens, regardless of what format it's meant to
    >>> cover. Its "light gathering power" is the same as any other lens of similar
    >>> f-number as far as photographic purposes are concerned, disregarding
    >>> differences in coating, etc.

    >>
    >> Of course it makes no sense: it is dead wrong.

    >
    > nope


    In what version of reality?

    >> If "bob" wrote that for the same 35mm equivalent FL that he was after
    >> the same DoF, then two stops wider aperture (for 4/3, in this case) will
    >> get the same DoF as FF (35mm full frame) at the same angle of view lens
    >> (35mm equiv focal length).
    >> It does not work for exposure, only DoF.

    >
    > then it's not equivalent, is it?


    Either you want the same DoF (then aperture setting AND shutter speed
    must change) or you want the same aperture AND shutter speed setting
    (then DoF will change).
    You can't have it both ways.

    >>> Even if you were right about that light-gathering business you'd be wrong in
    >>> your conclusion: a half-frame format does not have half the diagonal of full
    >>> frame. (It's 30mm vs about 43mm.)

    >>
    >> In this case (for 4/3), it is really a quarter-frame format (about 22mm
    >> Vs about 43mm diagonal).
    >> Not that I really believe that the facts will "get in the way" of "bob"s
    >> argument.

    >
    > they do for you though.


    That is a surprise.
    The facts demonstrably contradict what you are trying to portray as
    "reality".
    How does that make me "wrong"?
     
    dj_nme, Jun 15, 2011
    #18
  19. bob

    nospam Guest

    In article <4df7e87e$0$13391$>, dj_nme
    <> wrote:

    > >> You seem to have not grasped the reason why some people use the term
    > >> "equivalent f-stop" when taking 4/3, APS and FF.

    > >
    > > actually you haven't grasped it, since you contradict yourself below.

    >
    > No, I don't.
    > It is all about the same Dof and NOT about the same exposure settings.
    > Read what I wrote, not what you want to see.


    to have the same dof, you need 2 stops wider on 4/3rds, which is what i
    said.

    > >> Using FF as the baseline, all the others have greater Depth of Field
    > >> (DoF) with lenses of the same angle of view (IE: 35mm Equivalent Focal
    > >> Length [35mm EFL]) with the same f-stop setting.

    > >
    > > true, but smaller formats will have more noise (all other things being
    > > equal) so you don't get the same image.
    > >
    > > <http://clarkvision.com/imagedetail/dof_myth/index.html>

    >
    > This is relevant, how?


    it explains it.

    > >> "equivalent f-stop" is using a aperture (f-stop) setting that gives an
    > >> equivalent DoF to 35mm at their 35mm EFL, not the same exposure value at
    > >> the same shutter speed.

    > >
    > > right, which for 4/3rds, is 2 stops wider.

    >
    > For the same DoF, not exposure value.


    which means to be equivalent, it must be 2 stops wider.
     
    nospam, Jun 15, 2011
    #19
  20. bob

    nospam Guest

    In article <4df7ea5c$0$3035$>, dj_nme
    <> wrote:

    > >> If "bob" wrote that for the same 35mm equivalent FL that he was after
    > >> the same DoF, then two stops wider aperture (for 4/3, in this case) will
    > >> get the same DoF as FF (35mm full frame) at the same angle of view lens
    > >> (35mm equiv focal length).
    > >> It does not work for exposure, only DoF.

    > >
    > > then it's not equivalent, is it?

    >
    > Either you want the same DoF (then aperture setting AND shutter speed
    > must change) or you want the same aperture AND shutter speed setting
    > (then DoF will change).
    > You can't have it both ways.


    raise the iso on the larger sensor so you can use a smaller f/stop,
    which will match noise and dof and keep the exposure the same.
     
    nospam, Jun 15, 2011
    #20
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