OT: stops or EVs

Discussion in 'Digital Photography' started by Charles Schuler, Jan 23, 2007.

  1. I am teaching digital photography in my community and lean toward EVs as
    opposed to stops. I know that the two are equivalent, but I also know that
    they are not the same thing.

    My feeling is that f/stops or f-stops, technically speaking, should only
    refer only to the aperture of the lens. I fully understand that an
    equivalent exists by changing shutter speed or ISO or both. With all of the
    folks now entering digital photography as a hobby, it would be advantageous
    to clear this issue a bit.

    I also find that camera manuals lean towards EV.

    What are your thoughts?
     
    Charles Schuler, Jan 23, 2007
    #1
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  2. In article <>,
    Charles Schuler <> wrote:
    >I am teaching digital photography in my community and lean toward EVs as
    >opposed to stops.
    >
    >What are your thoughts?


    It depends on how you intend to use it. An EV is absolute value: it
    specifies a certain amount of light reaching the sensor. On the other hand,
    'stops' are often used to specify a difference in exposure: "underexpose by
    1 or 2 stops".


    --
    That was it. Done. The faulty Monk was turned out into the desert where it
    could believe what it liked, including the idea that it had been hard done
    by. It was allowed to keep its horse, since horses were so cheap to make.
    -- Douglas Adams in Dirk Gently's Holistic Detective Agency
     
    Philip Homburg, Jan 23, 2007
    #2
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  3. Charles Schuler

    Jim Guest

    Re: stops or EVs

    "Charles Schuler" <> wrote in message
    news:...
    >I am teaching digital photography in my community and lean toward EVs as
    >opposed to stops. I know that the two are equivalent, but I also know that
    >they are not the same thing.
    >
    > My feeling is that f/stops or f-stops, technically speaking, should only
    > refer only to the aperture of the lens. I fully understand that an
    > equivalent exists by changing shutter speed or ISO or both. With all of
    > the folks now entering digital photography as a hobby, it would be
    > advantageous to clear this issue a bit.
    >
    > I also find that camera manuals lean towards EV.
    >
    > What are your thoughts?
    >

    Many computer manuals have a chart which shows how the camera selects stops
    and shutter speeds as a function of the amount of light.
    The charts have vertical lines for shutter speed and horizontal lines for
    stop. There are also diagonal lines which are lines of constant EV.

    Jim
     
    Jim, Jan 23, 2007
    #3
  4. Charles Schuler wrote:
    > I am teaching digital photography in my community and lean toward EVs as
    > opposed to stops. I know that the two are equivalent, but I also know that
    > they are not the same thing.
    >
    > My feeling is that f/stops or f-stops, technically speaking, should only
    > refer only to the aperture of the lens. I fully understand that an
    > equivalent exists by changing shutter speed or ISO or both. With all of the
    > folks now entering digital photography as a hobby, it would be advantageous
    > to clear this issue a bit.
    >
    > I also find that camera manuals lean towards EV.
    >
    > What are your thoughts?


    EV is dead. Cameras are no longer marked in it, etc. Its use in
    manuals is an anachronism. It's just another thing to load into
    people's heads (they can't escape the need to know ISO, aperture, and
    shutter speed anyway), and it will just cause confusion and waste their
    time.
     
    David Dyer-Bennet, Jan 23, 2007
    #4
  5. Charles Schuler

    Peter Irwin Guest

    Charles Schuler <> wrote:
    > I am teaching digital photography in my community and lean toward EVs as
    > opposed to stops. I know that the two are equivalent, but I also know that
    > they are not the same thing.


    Using "stops" for exposure or even shutter speed is perfectly
    good photographic jargon. It is also perfectly reasonable to
    use the word "speed" or "fast" for aperture.

    So:
    1/250s is one stop less than 1/125s.
    or
    f/8 is twice the speed of f/11.

    are perfectly good and have been in regular use by photographers
    for most of the history of photography.

    You do need to avoid confusion, and there is an oddity in the
    vocabulary that a faster shutter speed produces less exposure
    while a "faster" aperture produces more exposure.

    >
    > My feeling is that f/stops or f-stops, technically speaking, should only
    > refer only to the aperture of the lens.


    I think that while you should make sure that you avoid confusion,
    the vocabulary of photography has always had a tradition of using
    speed terminology for aperture and aperture terminology for speed.
    This was clearly already very common in 1860 when a lens called
    the "rapid rectilinear" was introduced. Your students are going
    to discover that this is the way photographers have always talked,
    and I don't think it would do any good to avoid it.

    Peter.
    --
     
    Peter Irwin, Jan 23, 2007
    #5
  6. Charles Schuler

    Paul Mitchum Guest

    Charles Schuler <> wrote:

    > I am teaching digital photography in my community and lean toward EVs as
    > opposed to stops. I know that the two are equivalent, but I also know
    > that they are not the same thing.
    >
    > My feeling is that f/stops or f-stops, technically speaking, should only
    > refer only to the aperture of the lens. I fully understand that an
    > equivalent exists by changing shutter speed or ISO or both. With all of
    > the folks now entering digital photography as a hobby, it would be
    > advantageous to clear this issue a bit.
    >
    > I also find that camera manuals lean towards EV.
    >
    > What are your thoughts?


    First of all, the concept is more important than the name.

    But secondly: The concept can be illustrated by explaining the
    difference between the two names.

    So you talk about stops and relative aperture size, and how opening and
    closing the aperture by stops changes the exposure. In the infancy of
    photography, changing the aperture was the primary way of altering
    exposure, which is why the term 'stop' came to refer to the amount of
    light exposed.

    And then you move on to the EV chart, showing how changing different
    settings can compensate for each other, yielding the same exposure (same
    exposure, but perhaps different picture). The wikipedia article on EV is
    pretty good. <http://en.wikipedia.org/wiki/Exposure_value>

    One of the other commenters was correct, though, in that EV itself isn't
    widely used beyond the exposure compensation setting. Used that way,
    'EV' and 'stop' are pretty well synonymous.

    You can also go on a tangent from there into the Zone System. Wooooo!
     
    Paul Mitchum, Jan 24, 2007
    #6
  7. Charles Schuler

    Mark² Guest

    Re: stops or EVs

    Charles Schuler wrote:
    > I am teaching digital photography in my community and lean toward EVs
    > as opposed to stops. I know that the two are equivalent, but I also
    > know that they are not the same thing.
    >
    > My feeling is that f/stops or f-stops, technically speaking, should
    > only refer only to the aperture of the lens. I fully understand that
    > an equivalent exists by changing shutter speed or ISO or both. With
    > all of the folks now entering digital photography as a hobby, it
    > would be advantageous to clear this issue a bit.
    >
    > I also find that camera manuals lean towards EV.
    >
    > What are your thoughts?


    Exposure value and stops are not synonyms.

    If you are teaching students, you really should teach them the standard
    language they'll face in the industry...so in my opinion, they should become
    aquainted with the term "stops."

    --
    Images (Plus Snaps & Grabs) by Mark² at:
    www.pbase.com/markuson
     
    Mark², Jan 24, 2007
    #7
  8. Charles Schuler

    Bill Funk Guest

    On Tue, 23 Jan 2007 17:45:48 -0500, "Charles Schuler"
    <> wrote:

    >I am teaching digital photography in my community and lean toward EVs as
    >opposed to stops. I know that the two are equivalent, but I also know that
    >they are not the same thing.
    >
    >My feeling is that f/stops or f-stops, technically speaking, should only
    >refer only to the aperture of the lens. I fully understand that an
    >equivalent exists by changing shutter speed or ISO or both. With all of the
    >folks now entering digital photography as a hobby, it would be advantageous
    >to clear this issue a bit.
    >
    >I also find that camera manuals lean towards EV.
    >
    >What are your thoughts?
    >

    When I teach digital photography basics, I teach what aperture,
    shutter speed and ISO speed are.
    Then I teach that one EV is equal to one f-stop, or one doubleimng or
    halving of a shutter speed, or one doubling or halving of an ISO
    number.
    I think it's important to understand the basics first, then teach the
    way they interact, then teach how to understand the interaction with
    respect to getting he results you want.
    Because EV is used in many magazines and on-line articles, I think
    it's important to expose the photographers to it, so they can
    understand what's being said. Ignoring the term "EV" because you don't
    agree with it doesn't help.

    --
    Washington Post humorist
    Art Buchwald was eulogized
    by friends Friday after a
    long and hilarious career.
    Reports of his death may be
    exaggerated. Every comedian
    thought he had died and gone
    to heaven when Hillary Clinton
    announced she is running for
    president.
     
    Bill Funk, Jan 24, 2007
    #8
  9. Charles Schuler

    Neil Ellwood Guest

    On Tue, 23 Jan 2007 17:45:48 -0500, Charles Schuler wrote:

    > I am teaching digital photography in my community and lean toward EVs as
    > opposed to stops. I know that the two are equivalent, but I also know that
    > they are not the same thing.
    >
    > My feeling is that f/stops or f-stops, technically speaking, should only
    > refer only to the aperture of the lens. I fully understand that an
    > equivalent exists by changing shutter speed or ISO or both. With all of the
    > folks now entering digital photography as a hobby, it would be advantageous
    > to clear this issue a bit.
    >
    > I also find that camera manuals lean towards EV.
    >
    > What are your thoughts?


    If you are teaching photography - God help your students.

    --
    Neil
    Reverse 'r' and 'a', delete 'l' for email.
     
    Neil Ellwood, Jan 24, 2007
    #9
  10. Charles Schuler

    Cgiorgio Guest

    Re: stops or EVs

    "Charles Schuler" <> schrieb im Newsbeitrag
    news:...
    >I am teaching digital photography in my community and lean toward EVs as
    >opposed to stops. I know that the two are equivalent, but I also know that
    >they are not the same thing.
    >
    > My feeling is that f/stops or f-stops, technically speaking, should only
    > refer only to the aperture of the lens. I fully understand that an
    > equivalent exists by changing shutter speed or ISO or both. With all of
    > the folks now entering digital photography as a hobby, it would be
    > advantageous to clear this issue a bit.
    >
    > I also find that camera manuals lean towards EV.
    >
    > What are your thoughts?

    I think the easiest way to explain about EV's, f-stops and shutter speeds is
    to explain how an old fashioned analogue exposure meter is used if you have
    one. Then discuss how aperture values and focal lengths affect depth of
    field and what the minimum shutter speeds for a given focal length should
    be.

    EV is probably useful to describe the dynamic range of the sensor and for
    estimating the effect an exposure compensation setting will give on a
    camera.
     
    Cgiorgio, Jan 24, 2007
    #10
  11. Charles Schuler

    Colin_D Guest

    Charles Schuler wrote:
    > I am teaching digital photography in my community and lean toward EVs as
    > opposed to stops. I know that the two are equivalent, but I also know that
    > they are not the same thing.
    >
    > My feeling is that f/stops or f-stops, technically speaking, should only
    > refer only to the aperture of the lens. I fully understand that an
    > equivalent exists by changing shutter speed or ISO or both. With all of the
    > folks now entering digital photography as a hobby, it would be advantageous
    > to clear this issue a bit.
    >
    > I also find that camera manuals lean towards EV.
    >
    > What are your thoughts?
    >
    >

    My opinion is that teaching just EV won't be enough, but it depends on
    what level of proficiency you are aiming at, and what sort of cameras
    you students will be using.

    EV is a simplification introduced to make it easier for non-photogs to
    be able to use metered cameras without knowledge of aperture/shutter
    interaction. At one time, some cameras used a mechanical coupling
    between shutter and aperture marked with EV values to assist with this,
    but I think those are now obsolete. If your students' cameras don't
    have EV scales, I think it's pointless to teach exposure etc. from an EV
    standpoint.

    EV tells you nothing about the characteristics of stops/aperture. The
    term 'stop' arose in the days before variable diaphragms were used.
    Discs with various sized holes (Waterhouse stops, named after the
    inventor, I guess) were placed in front of, or in a slot in the lens, to
    control exposure and depth of field.

    The major effects of varying the aperture need to be well understood by
    students, from shallow depth to great depth of field, plus the effect on
    some lens aberrations, the concept of diffraction limits and Airey Disc
    definition limitations with very small apertures.

    None of this fundamental knowledge is even hinted at by teaching EV alone.

    Nor is the effect of shutter speed on subject movement, camera shake,
    and reciprocity failure with film. Reciprocity is not a problem with
    digital, but IMO if your students are to have a good grounding, they
    should be aware if they find themselves using film. They may well
    graduate to a MF or LF camera.

    Colin D.

    --
    Posted via a free Usenet account from http://www.teranews.com
     
    Colin_D, Jan 24, 2007
    #11
  12. "Neil Ellwood" <> wrote in message
    news:...
    > On Tue, 23 Jan 2007 17:45:48 -0500, Charles Schuler wrote:
    >
    >> I am teaching digital photography in my community and lean toward EVs as
    >> opposed to stops. I know that the two are equivalent, but I also know
    >> that
    >> they are not the same thing.
    >>
    >> My feeling is that f/stops or f-stops, technically speaking, should only
    >> refer only to the aperture of the lens. I fully understand that an
    >> equivalent exists by changing shutter speed or ISO or both. With all of
    >> the
    >> folks now entering digital photography as a hobby, it would be
    >> advantageous
    >> to clear this issue a bit.
    >>
    >> I also find that camera manuals lean towards EV.
    >>
    >> What are your thoughts?

    >
    > If you are teaching photography - God help your students.


    What is it with assholes like you? I think it was an interesting question,
    but you had to respond with vitriol. Piss off.
     
    Charles Schuler, Jan 24, 2007
    #12
  13. Charles Schuler

    J. Clarke Guest

    On Thu, 25 Jan 2007 11:38:46 +1300, Colin_D <nospam@127.0.0.1> wrote:

    >Charles Schuler wrote:
    >> I am teaching digital photography in my community and lean toward EVs as
    >> opposed to stops. I know that the two are equivalent, but I also know that
    >> they are not the same thing.
    >>
    >> My feeling is that f/stops or f-stops, technically speaking, should only
    >> refer only to the aperture of the lens. I fully understand that an
    >> equivalent exists by changing shutter speed or ISO or both. With all of the
    >> folks now entering digital photography as a hobby, it would be advantageous
    >> to clear this issue a bit.
    >>
    >> I also find that camera manuals lean towards EV.
    >>
    >> What are your thoughts?
    >>
    >>

    >My opinion is that teaching just EV won't be enough, but it depends on
    >what level of proficiency you are aiming at, and what sort of cameras
    >you students will be using.
    >
    >EV is a simplification introduced to make it easier for non-photogs to
    >be able to use metered cameras without knowledge of aperture/shutter
    >interaction. At one time, some cameras used a mechanical coupling
    >between shutter and aperture marked with EV values to assist with this,
    >but I think those are now obsolete. If your students' cameras don't
    >have EV scales, I think it's pointless to teach exposure etc. from an EV
    >standpoint.
    >
    >EV tells you nothing about the characteristics of stops/aperture. The
    >term 'stop' arose in the days before variable diaphragms were used.
    >Discs with various sized holes (Waterhouse stops, named after the
    >inventor, I guess) were placed in front of, or in a slot in the lens, to
    >control exposure and depth of field.
    >
    >The major effects of varying the aperture need to be well understood by
    >students, from shallow depth to great depth of field, plus the effect on
    >some lens aberrations, the concept of diffraction limits and Airey Disc
    >definition limitations with very small apertures.
    >
    >None of this fundamental knowledge is even hinted at by teaching EV alone.
    >
    >Nor is the effect of shutter speed on subject movement, camera shake,
    >and reciprocity failure with film. Reciprocity is not a problem with
    >digital, but IMO if your students are to have a good grounding, they
    >should be aware if they find themselves using film. They may well
    >graduate to a MF or LF camera.


    Seems to me that one should know aperture and shutter speed and EV as
    well--I don't see it as "either/or".
     
    J. Clarke, Jan 25, 2007
    #13
  14. "Charles Schuler" <> writes:
    > I am teaching digital photography in my community and lean toward
    > EVs as opposed to stops. I know that the two are equivalent, but I
    > also know that they are not the same thing.
    >
    > My feeling is that f/stops or f-stops, technically speaking, should
    > only refer only to the aperture of the lens. I fully understand
    > that an equivalent exists by changing shutter speed or ISO or both.
    > With all of the folks now entering digital photography as a hobby,
    > it would be advantageous to clear this issue a bit.
    >
    > I also find that camera manuals lean towards EV.
    >
    > What are your thoughts?


    EV (or both). They are only equivalent in certain contexts.

    Knowing about absolute EV as a specific quantity of light
    (see: http://hannemyr.com/photo/ir.html#ev ) is important.
    There is no sensible way to get this concept across using
    stops.

    Personally I also think that talking about various types of
    exposure compensation, such as FEC, in terms of EV is much
    more intutive than using stops. "Adjust your flash up two
    stops" sounds strange in my ears, but "Dial in +2 EV on your
    flash" makes sense.

    All handheld spot meters, and many handheld average meters are
    reporting light as EV, and I don't think that will change.
    If they are going to learn how to use a manual light meter,
    they need to understand EV.

    If your students are going to learn advanced subjects, such as
    the Zone System - http://hannemyr.com/photo/zonesystem.html -
    they need to know avout EV.

    So I think your instincts are right. EV is not obsolete and
    photography students need to know about EV.

    They also need to know that when one is talking about aperture
    adjustments, EV and stops are equivalent, and that many people
    use the term "stop" as a synonym for "EV" when discussing
    halving our doubling the shutter speed or ISO. But EV is
    used in so many contexts where "stop" will not do, that I think
    that the best approach when teaching is to introduce it its
    own right.
    --
    - gisle hannemyr [ gisle{at}hannemyr.no - http://hannemyr.com/photo/ ]
    ------------------------------------------------------------------------
    Sigma SD10, Kodak DCS460, Canon Powershot G5, Olympus 2020Z
    ------------------------------------------------------------------------
     
    Gisle Hannemyr, Jan 25, 2007
    #14
  15. Charles Schuler

    Colin_D Guest

    J. Clarke wrote:
    > On Thu, 25 Jan 2007 11:38:46 +1300, Colin_D <nospam@127.0.0.1> wrote:
    >
    >> Charles Schuler wrote:
    >>> I am teaching digital photography in my community and lean toward EVs as
    >>> opposed to stops. I know that the two are equivalent, but I also know that
    >>> they are not the same thing.
    >>>
    >>> My feeling is that f/stops or f-stops, technically speaking, should only
    >>> refer only to the aperture of the lens. I fully understand that an
    >>> equivalent exists by changing shutter speed or ISO or both. With all of the
    >>> folks now entering digital photography as a hobby, it would be advantageous
    >>> to clear this issue a bit.
    >>>
    >>> I also find that camera manuals lean towards EV.
    >>>
    >>> What are your thoughts?
    >>>
    >>>

    >> My opinion is that teaching just EV won't be enough, but it depends on
    >> what level of proficiency you are aiming at, and what sort of cameras
    >> you students will be using.
    >>
    >> EV is a simplification introduced to make it easier for non-photogs to
    >> be able to use metered cameras without knowledge of aperture/shutter
    >> interaction. At one time, some cameras used a mechanical coupling
    >> between shutter and aperture marked with EV values to assist with this,
    >> but I think those are now obsolete. If your students' cameras don't
    >> have EV scales, I think it's pointless to teach exposure etc. from an EV
    >> standpoint.
    >>
    >> EV tells you nothing about the characteristics of stops/aperture. The
    >> term 'stop' arose in the days before variable diaphragms were used.
    >> Discs with various sized holes (Waterhouse stops, named after the
    >> inventor, I guess) were placed in front of, or in a slot in the lens, to
    >> control exposure and depth of field.
    >>
    >> The major effects of varying the aperture need to be well understood by
    >> students, from shallow depth to great depth of field, plus the effect on
    >> some lens aberrations, the concept of diffraction limits and Airey Disc
    >> definition limitations with very small apertures.
    >>
    >> None of this fundamental knowledge is even hinted at by teaching EV alone.
    >>
    >> Nor is the effect of shutter speed on subject movement, camera shake,
    >> and reciprocity failure with film. Reciprocity is not a problem with
    >> digital, but IMO if your students are to have a good grounding, they
    >> should be aware if they find themselves using film. They may well
    >> graduate to a MF or LF camera.

    >
    > Seems to me that one should know aperture and shutter speed and EV as
    > well--I don't see it as "either/or".
    >

    Well, your in your OP you implied that you want to teach EV in
    preference to stops, and that is what I and others have replied to.

    Colin D.

    --
    Posted via a free Usenet account from http://www.teranews.com
     
    Colin_D, Jan 25, 2007
    #15
  16. (Philip Homburg) writes:

    > It depends on how you intend to use it. An EV is absolute value: it
    > specifies a certain amount of light reaching the sensor. On the
    > other hand, 'stops' are often used to specify a difference in
    > exposure: "underexpose by 1 or 2 stops".


    No, that is an LV. EV are shutter speed/f stop pairs that are only
    equal to LVs if you are using 100asa film, or equivalent. Find an old
    Rollie TLR or 'blad and play with the setting.
     
    Paul Repacholi, Jan 27, 2007
    #16
  17. Gisle Hannemyr <> writes:

    > Knowing about absolute EV as a specific quantity of light
    > (see: http://hannemyr.com/photo/ir.html#ev ) is important.


    NO it is NOT! This is so far out, it is not even wrong! The
    related number for light values is LV. EV is only a speed/f#
    pairingand is not related at all to LV unless you specify
    a film speed as well.

    If you are going to teach it, get it 100% right, there is no excuse
    not to.

    ------------ And now a word from our sponsor ---------------------
    For a secure high performance FTP using SSL/TLS encryption
    upgrade to SurgeFTP
    ---- See http://netwinsite.com/sponsor/sponsor_surgeftp.htm ----
     
    Paul Repacholi, Jan 27, 2007
    #17
  18. In article <>,
    Paul Repacholi <> wrote:
    > (Philip Homburg) writes:
    >
    >> It depends on how you intend to use it. An EV is absolute value: it
    >> specifies a certain amount of light reaching the sensor. On the
    >> other hand, 'stops' are often used to specify a difference in
    >> exposure: "underexpose by 1 or 2 stops".

    >
    >No, that is an LV. EV are shutter speed/f stop pairs that are only
    >equal to LVs if you are using 100asa film, or equivalent. Find an old
    >Rollie TLR or 'blad and play with the setting.


    Yes, you are right. EV is more like the amount of light as a function
    of the subject brightness.





    --
    That was it. Done. The faulty Monk was turned out into the desert where it
    could believe what it liked, including the idea that it had been hard done
    by. It was allowed to keep its horse, since horses were so cheap to make.
    -- Douglas Adams in Dirk Gently's Holistic Detective Agency
     
    Philip Homburg, Jan 27, 2007
    #18
  19. Re: stops or EVs

    "Charles Schuler" <> wrote in message
    news:...
    >I am teaching digital photography in my community and lean toward EVs as
    >opposed to stops. I know that the two are equivalent, but I also know that
    >they are not the same thing.
    >
    > My feeling is that f/stops or f-stops, technically speaking, should only
    > refer only to the aperture of the lens. I fully understand that an
    > equivalent exists by changing shutter speed or ISO or both. With all of
    > the folks now entering digital photography as a hobby, it would be
    > advantageous to clear this issue a bit.


    I know that stops are different things than exposure values. My point
    was/is about discussing changes: delta stops = delta EVs (a change of one
    stop is equal to a change of one EV). One can achieve an exposure change by
    varying aperture, shutter speed or ISO (or any combination). I like EV
    because it is a more general concept and fits better with light meters, etc.

    However, the common vernacular heavily favors stops. That doesn't mean it
    is necessarily the best way to teach it.

    Photography is not rocket science but it can be confusing for beginners.

    Thanks to all who responded (well, mostly).
     
    Charles Schuler, Jan 27, 2007
    #19
  20. Charles Schuler

    King Sardon Guest

    Re: stops or EVs

    On Sat, 27 Jan 2007 16:18:08 -0500, "Charles Schuler"
    <> wrote:

    >
    >"Charles Schuler" <> wrote in message
    >news:...
    >>I am teaching digital photography in my community and lean toward EVs as
    >>opposed to stops. I know that the two are equivalent, but I also know that
    >>they are not the same thing.
    >>
    >> My feeling is that f/stops or f-stops, technically speaking, should only
    >> refer only to the aperture of the lens. I fully understand that an
    >> equivalent exists by changing shutter speed or ISO or both. With all of
    >> the folks now entering digital photography as a hobby, it would be
    >> advantageous to clear this issue a bit.

    >
    >I know that stops are different things than exposure values. My point
    >was/is about discussing changes: delta stops = delta EVs (a change of one
    >stop is equal to a change of one EV). One can achieve an exposure change by
    >varying aperture, shutter speed or ISO (or any combination). I like EV
    >because it is a more general concept and fits better with light meters, etc.
    >
    >However, the common vernacular heavily favors stops. That doesn't mean it
    >is necessarily the best way to teach it.


    IIRC, a "stop" was originally (in the real old days) a small opaque
    plate with a hole in it of a particular size that was inserted
    transversely into a lens to control the amount of light. The stop
    wasn't the aperture, it was the opaque part. And the different hole
    sizes usually didn't vary by factors of 2.

    So today's meaning of stop = 2-fold change in aperture cross-sectional
    area isn't really accurate either.

    KS
     
    King Sardon, Jan 27, 2007
    #20
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