Fixed Aperture Pentax Zoom

Discussion in 'Pentax' started by Wayne R., Jan 31, 2009.

  1. Wayne R.

    Wayne R. Guest

    I understand that the kit's zoom lenses with my Pentax K100D Super are
    variable aperture types. What do I look for in their lens list to find
    info on a zoom that's non-variable?

    My understanding is that the aperture varies depending on how the
    zoom's set, or, in other words, the exposure changes as the zoom
    moves. (Tried to look it up right now but Google's busted.)

    Do I have that right? How does the camera function in aperture
    priority mode with this situation? Can I expect to see anything odd
    with this type of lens?

    This kind of lens is a surprise to me...
     
    Wayne R., Jan 31, 2009
    #1
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  2. Wayne R.

    Peter Guest

    "Wayne R." <> wrote in message
    news:...
    >I understand that the kit's zoom lenses with my Pentax K100D Super are
    > variable aperture types. What do I look for in their lens list to find
    > info on a zoom that's non-variable?
    >
    > My understanding is that the aperture varies depending on how the
    > zoom's set, or, in other words, the exposure changes as the zoom
    > moves. (Tried to look it up right now but Google's busted.)
    >
    > Do I have that right? How does the camera function in aperture
    > priority mode with this situation? Can I expect to see anything odd
    > with this type of lens?
    >
    > This kind of lens is a surprise to me...



    Try the Nikon 80-200 f2.8, 70-200 f2.8, 200-400 f4.

    The above are not cheap. For use on other cameras, Google is your friend.
    --
    Peter
     
    Peter, Jan 31, 2009
    #2
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  3. Wayne R.

    nospam Guest

    In article <>, Wayne R.
    <> wrote:

    > I understand that the kit's zoom lenses with my Pentax K100D Super are
    > variable aperture types. What do I look for in their lens list to find
    > info on a zoom that's non-variable?


    one f/stop as opposed to a range. for instance, pentax has a 16-45mm
    f/4 and a 18-55mm f/3.5-5.6.

    > My understanding is that the aperture varies depending on how the
    > zoom's set, or, in other words, the exposure changes as the zoom
    > moves. (Tried to look it up right now but Google's busted.)
    >
    > Do I have that right? How does the camera function in aperture
    > priority mode with this situation? Can I expect to see anything odd
    > with this type of lens?


    no issue at all. the camera's meter handles it just fine.

    > This kind of lens is a surprise to me...


    very common and less expensive to make.
     
    nospam, Jan 31, 2009
    #3
  4. Wayne R.

    Joel Guest

    In general

    1. Fast Lens = means "better glass" and better class is more capable of
    capturing sharper image, as well as fast focus

    2. Most people mention getting fast lens f2.8 or faster doesn't mean to use
    the lens to shoot at F2.8, f2.0, f1.8, f1.2 etc.. but it means the glass is
    able to capture acceptable quality at F1.2 -> F2.8 etc..

    3. Fast Focus, meaning it spends less time to focus which mean you have more
    chance to capture sharp image. Less chance to get shaking and blurry image
    etc..

    Yes, f3.5 or f4 lens should be able to capture sharp image too, but it
    will require extra work to get sharp image comparing to Good Glass.

    So, keep in mind when someone suggest getting F2.8 or better lens doesn't
    mean to shoort at F2.8, but YOU GET WHAT YOU PAY FOR.
     
    Joel, Jan 31, 2009
    #4
  5. Wayne R.

    Joel Guest

    Alan Browne <> wrote:

    > Joel wrote:
    > > In general
    > >
    > > 1. Fast Lens = means "better glass" and better class is more capable of
    > > capturing sharper image, as well as fast focus

    >
    > Actually "Fast" means the larger apertures for the focal length and lens
    > class. These typically have "better glass" as well, but that has
    > negligible affect on light transmissivity.


    And larger aperature means faster lens, better glass, better glass has
    more chance to capture sharp image right?

    I think I have them all covered.
     
    Joel, Jan 31, 2009
    #5
  6. Wayne R.

    Pete D Guest

    "Peter" <> wrote in message
    news:49847bc6$0$31170$-secrets.com...
    > "Wayne R." <> wrote in message
    > news:...
    >>I understand that the kit's zoom lenses with my Pentax K100D Super are
    >> variable aperture types. What do I look for in their lens list to find
    >> info on a zoom that's non-variable?
    >>
    >> My understanding is that the aperture varies depending on how the
    >> zoom's set, or, in other words, the exposure changes as the zoom
    >> moves. (Tried to look it up right now but Google's busted.)
    >>
    >> Do I have that right? How does the camera function in aperture
    >> priority mode with this situation? Can I expect to see anything odd
    >> with this type of lens?
    >>
    >> This kind of lens is a surprise to me...

    >
    >
    > Try the Nikon 80-200 f2.8, 70-200 f2.8, 200-400 f4.
    >
    > The above are not cheap. For use on other cameras, Google is your friend.
    > --
    > Peter


    Um, how would that help on his Pentax camera?
     
    Pete D, Jan 31, 2009
    #6
  7. Wayne R.

    Joel Guest

    Alan Browne <> wrote:

    > Joel wrote:
    > > Alan Browne <> wrote:
    > >
    > >> Joel wrote:
    > >>> In general
    > >>>
    > >>> 1. Fast Lens = means "better glass" and better class is more capable of
    > >>> capturing sharper image, as well as fast focus
    > >> Actually "Fast" means the larger apertures for the focal length and lens
    > >> class. These typically have "better glass" as well, but that has
    > >> negligible affect on light transmissivity.

    > >
    > > And larger aperature means faster lens, better glass, better glass has
    > > more chance to capture sharp image right?
    > >
    > > I think I have them all covered.

    >
    > It principally and classically means the aperture.
    >
    > The word "fast" comes as a consequence of shutter speed.
    >
    > The higher quality of material used contributes to sharpness, but so
    > does the critical lens shape, assembly design and manufacturing.
    >
    > You're the one who put the "=" sign.


    Nope! Fast Lens really mean Fast Focus *not* shuttle speed which is the
    job of the camera.

    And Larger Aperature means Better Glass and Better Glass means can FOCUS
    *faster* than small Aperature or slower lens.
     
    Joel, Jan 31, 2009
    #7
  8. Wayne R.

    Peter Guest

    "Pete D" <> wrote in message
    news:4984d177$0$18773$...
    >
    > "Peter" <> wrote in message
    > news:49847bc6$0$31170$-secrets.com...
    >> "Wayne R." <> wrote in message
    >> news:...
    >>>I understand that the kit's zoom lenses with my Pentax K100D Super are
    >>> variable aperture types. What do I look for in their lens list to find
    >>> info on a zoom that's non-variable?
    >>>
    >>> My understanding is that the aperture varies depending on how the
    >>> zoom's set, or, in other words, the exposure changes as the zoom
    >>> moves. (Tried to look it up right now but Google's busted.)
    >>>
    >>> Do I have that right? How does the camera function in aperture
    >>> priority mode with this situation? Can I expect to see anything odd
    >>> with this type of lens?
    >>>
    >>> This kind of lens is a surprise to me...

    >>
    >>
    >> Try the Nikon 80-200 f2.8, 70-200 f2.8, 200-400 f4.
    >>
    >> The above are not cheap. For use on other cameras, Google is your friend.
    >> --
    >> Peter

    >
    > Um, how would that help on his Pentax camera?



    I understood the OP to ask whether there were fixed maximum aperture zooms.
    My answer was yes, with examples. And that he/she could Google to see if
    there were any for a Pentax. I think that was about as complete an answer as
    I could give.

    --
    Peter
     
    Peter, Feb 1, 2009
    #8
  9. Wayne R.

    nospam Guest

    In article <4984f7d5$0$31176$-secrets.com>, Peter
    <> wrote:

    > >>>I understand that the kit's zoom lenses with my Pentax K100D Super are
    > >>> variable aperture types. What do I look for in their lens list to find
    > >>> info on a zoom that's non-variable?


    > >> Try the Nikon 80-200 f2.8, 70-200 f2.8, 200-400 f4.
    > >>
    > >> The above are not cheap. For use on other cameras, Google is your friend.


    > > Um, how would that help on his Pentax camera?

    >
    > I understood the OP to ask whether there were fixed maximum aperture zooms.


    he said he had a pentax camera and specifically asked about 'their lens
    list,' or in other words, pentax lenses.

    > My answer was yes, with examples. And that he/she could Google to see if
    > there were any for a Pentax. I think that was about as complete an answer as
    > I could give.


    complete yes, but he more than likely was not interested in anything
    other than pentax lenses.
     
    nospam, Feb 1, 2009
    #9
  10. "dadiOH" <> wrote in message
    news:ph5hl.616$2...

    > There are such things as constant aperture zoom lenses. They are
    > expensive. I have never seen one and have no idea how they overcome the
    > above but I suspect via magic :)


    I have a copy of Pentax's f3.5 35-105mm . I remember wondering how it worked
    much as you did. I ran through the zoom with the lens unmounted, and, as
    near as I can tell, the iris seems to simply close a little at the shorter
    end. The amount of speed lost would be minimal - probably only a fraction of
    a stop - so I have to assume that it's sacrificed in aid of easier or more
    consistent exposure calculation.

    Unless it's magic.;-)
     
    Norman Weaver, Feb 1, 2009
    #10
  11. Wayne R.

    Joel Guest

    Alan Browne <> wrote:

    > Joel wrote:
    > > Alan Browne <> wrote:
    > >
    > >> Joel wrote:

    >
    > >> It principally and classically means the aperture.
    > >>
    > >> The word "fast" comes as a consequence of shutter speed.
    > >>
    > >> The higher quality of material used contributes to sharpness, but
    > >> so does the critical lens shape, assembly design and manufacturing.
    > >>
    > >>
    > >> You're the one who put the "=" sign.

    > >
    > > Nope! Fast Lens really mean Fast Focus *not* shuttle speed which is
    > > the job of the camera.

    >
    > No. No. No.
    >
    > Fast means larger aperture which leads to _faster_ shutter speed (the
    > setting, not the lag) due to reciprocity. That's where the 'fast' comes
    > from.
    >
    > (eg: 1/500 @ f/2.8 is faster than 1/125 @ f/5.6
    > The above is the same exposure, but 1/500 is faster. Get it?)
    >
    >
    > It has NEVER meant anything else.
    > =================================
    >
    > > And Larger Aperature means Better Glass and Better Glass means can
    > > FOCUS *faster* than small Aperature or slower lens.

    >
    > Faster focus with faster lenses is simply because there is more light
    > (contrast) for the AF to work with so it can close the loop quicker.


    So, does it mean some top-of-the-line-lens (we are looking at $500-10000+
    lens) f4 and f5 lens are Slow Lens?. Because even they are the most
    expensive lens but they are F4 and F5 lenses.
     
    Joel, Feb 1, 2009
    #11
  12. Wayne R.

    Joel Guest

    "Norman Weaver" <> wrote:

    >
    > "dadiOH" <> wrote in message
    > news:ph5hl.616$2...
    >
    > > There are such things as constant aperture zoom lenses. They are
    > > expensive. I have never seen one and have no idea how they overcome the
    > > above but I suspect via magic :)

    >
    > I have a copy of Pentax's f3.5 35-105mm . I remember wondering how it worked
    > much as you did. I ran through the zoom with the lens unmounted, and, as
    > near as I can tell, the iris seems to simply close a little at the shorter
    > end. The amount of speed lost would be minimal - probably only a fraction of
    > a stop - so I have to assume that it's sacrificed in aid of easier or more
    > consistent exposure calculation.
    >
    > Unless it's magic.;-)


    It sounds like a magical lens too me. How about comparing your Pentax
    f3.5 35-105mm to either Canon 200-400L F4 or 800mm F5.x etc..

    The lens sport photographers use.
     
    Joel, Feb 1, 2009
    #12
  13. Wayne R.

    Wayne R. Guest

    On Sat, 31 Jan 2009 18:39:21 -0500, "dadiOH" <>
    wrote (with clarity & insight):

    >Any lens has both a maximum and minimum diameter opening in the diaphragm.
    >The f-stop of a lens is expressed by the formula, f-stop = Focal
    >Length/Aperture. That means that a lens with a greater focal length has to
    >have a greater aperture than a shorter lens with the same f-stop.
    >
    >That means that with most zoom lenses the f-stop - not the aperture, just
    >the f-stop - will become larger as one zooms out the lens; larger f-stop
    >means smaller aperture and that means less light enters the lens. If you
    >shoot in aperture priority mode, the shutter speed will be slowed to
    >compensate for the smaller aperture; in shutter priority, the aperture is
    >automatically adjusted (up to its maximum/minimum physical limits).
    >
    >There are such things as constant aperture zoom lenses. They are expensive.
    >I have never seen one and have no idea how they overcome the above but I
    >suspect via magic :)


    That zoom lenses are inherently variable (in focal length and in
    f-stop too) certainly makes the most sense. Thanks!

    Years ago I worked in video (mid-quality, not a lot of hard-core
    broadcast quality) and all the cameras had zoom lenses. I don't
    believe, though, that there was any compensation for this effect,
    either mechanical or electrical.

    No magic and no apparent effect either. And, since there would be
    several cameras shooting the same scene and all their video controls
    were centralized in the control room or van, I would've thought that
    we'd have seen some fluctuation in the effective exposure, either via
    eyeball or in the waveform monitors. Maybe we just didn't know to look
    for it.
     
    Wayne R., Feb 1, 2009
    #13
  14. Wayne R.

    Robert Coe Guest

    On Sat, 31 Jan 2009 10:17:22 -0500, Wayne R. <> wrote:
    : I understand that the kit's zoom lenses with my Pentax K100D Super are
    : variable aperture types. What do I look for in their lens list to find
    : info on a zoom that's non-variable?
    :
    : My understanding is that the aperture varies depending on how the
    : zoom's set, or, in other words, the exposure changes as the zoom
    : moves. (Tried to look it up right now but Google's busted.)
    :
    : Do I have that right? How does the camera function in aperture
    : priority mode with this situation? Can I expect to see anything odd
    : with this type of lens?
    :
    : This kind of lens is a surprise to me...

    The "f-stop" of a lens is the ratio of its focal length to the diameter of the
    aperture to which it is set. Typically the "speed" (a slang term for the
    light-gathering power) of a lens is expressed in terms of the maximum f-stop
    to which it can be set. So a 50mm f/2 lens has a maximum aperture of 25mm.

    But suppose instead you design a lens of the same diameter to be a 50-100mm
    zoom. At the 50mm end of its range it will still be an f/2 lens, because its
    focal length is still twice the 25mm diameter of its maximum aperture. But at
    the 100mm end it will be an f/4 lens, because 100mm is four times the maximum
    diameter (which of course is still 25mm). Note that the correct amount of
    light still reaches the metering system; but the lens does have to report the
    correct f-stop for any setting of the aperture and the focal length, since a
    change in either will affect it.

    But suppose you want to build a "constant aperture" zoom lens, in which the
    maximum f-stop at both ends of the zoom range is the same. You can't just
    ignore the effect of changing the focal length (it's a law of physics), nor
    can you change the diameter of the lens (it would have the desired effect, but
    glass doesn't stretch very well). But what you can do is *pretend* to change
    the diameter by using less of it at the low end of the range than at the high
    end. Since a zoom lens's optical challenges tend to be greater at the low end
    anyway, limiting the aperture at that end may actually make the lens easier to
    design.

    Because of their design constraints constant aperture zooms are bigger and
    heavier and have a shorter zoom range than their variable-aperture cousins.
    Contrary to what you've been told, they're not unaffordable, although their
    inherent limitations might be prohibitively expensive to overcome. A constant
    aperture superzoom would presumably be a costly - and heavy - animal indeed.

    I have two C-A zooms, both made by Sigma, for my Canons: an 18-50mm f/2.8 and
    a 50-150mm f/2.8. Both have pretty good optical quality, and their total cost
    was under $1200. But a single modern superzoom might cover the same range for
    less money. So if you don't do as much indoor photography as I do, and
    therefore don't need the wide aperture at all focal lengths, a constant
    aperture zoom may not make a lot of sense.

    Bob
     
    Robert Coe, Feb 1, 2009
    #14
  15. Wayne R.

    OG Guest

    "Joel" <> wrote in message
    news:p...
    > Alan Browne <> wrote:
    >
    >> Joel wrote:
    >> > Alan Browne <> wrote:
    >> >
    >> >> Joel wrote:

    >>
    >> >> It principally and classically means the aperture.
    >> >>
    >> >> The word "fast" comes as a consequence of shutter speed.
    >> >>
    >> >> The higher quality of material used contributes to sharpness, but
    >> >> so does the critical lens shape, assembly design and manufacturing.
    >> >>
    >> >>
    >> >> You're the one who put the "=" sign.
    >> >
    >> > Nope! Fast Lens really mean Fast Focus *not* shuttle speed which is
    >> > the job of the camera.

    >>
    >> No. No. No.
    >>
    >> Fast means larger aperture which leads to _faster_ shutter speed (the
    >> setting, not the lag) due to reciprocity. That's where the 'fast' comes
    >> from.
    >>
    >> (eg: 1/500 @ f/2.8 is faster than 1/125 @ f/5.6
    >> The above is the same exposure, but 1/500 is faster. Get it?)
    >>
    >>
    >> It has NEVER meant anything else.
    >> =================================
    >>
    >> > And Larger Aperature means Better Glass and Better Glass means can
    >> > FOCUS *faster* than small Aperature or slower lens.

    >>
    >> Faster focus with faster lenses is simply because there is more light
    >> (contrast) for the AF to work with so it can close the loop quicker.

    >
    > So, does it mean some top-of-the-line-lens (we are looking at $500-10000+
    > lens) f4 and f5 lens are Slow Lens?. Because even they are the most
    > expensive lens but they are F4 and F5 lenses.


    Joel , accept that you made a mistake in thinking you knew why some lenses
    are described as 'fast'

    Lenses are designed to have particular characteristics and are given a
    description that matches the prominent feature of the design. As with many
    things, the final design is a compromise between features, so the way the
    lens is designed would generally emphasise the design characteristic that
    has selected to drive the design.

    An expensive f/4 or f/5 lens will have been designed to produce a lens with
    certain characteristics, such as low aberrations, minimal vignetting, close
    focus or macro capability etc. Part of the compromise will be that the
    maximum aperture will be limited. These lenses would be described by
    reference to the selected design features.

    There is a type of lens in which the design has been chosen to give a wide
    maximum aperture. These are known as 'fast' lenses because they allow faster
    shutter speeds for a particular light level. Indeed, it would be quite
    common for a 'fast' lens to have serious compromises in other aspects of its
    design. If another lens has been designed to emphasise some other
    characteristic they would be given a different description.

    Yes, you /could/ describe the expensive totl lenses as 'slow', but it would
    be more usual to give them a description that more accurately reflected the
    positive charateristics of the lens design.

    The description of lenses as 'fast' or 'slow' dates back many decades - well
    before the days of auto focus. And (would you believe it) some of us still
    use these lenses!
     
    OG, Feb 1, 2009
    #15
  16. Wayne R.

    Joel Guest

    Alan Browne <> wrote:

    > Joel wrote:
    > > Alan Browne <> wrote:
    > >
    > >> Joel wrote:
    > >>> Alan Browne <> wrote:
    > >>>
    > >>>> Joel wrote:
    > >>>> It principally and classically means the aperture.
    > >>>>
    > >>>> The word "fast" comes as a consequence of shutter speed.
    > >>>>
    > >>>> The higher quality of material used contributes to sharpness, but
    > >>>> so does the critical lens shape, assembly design and manufacturing.
    > >>>>
    > >>>>
    > >>>> You're the one who put the "=" sign.
    > >>> Nope! Fast Lens really mean Fast Focus *not* shuttle speed which is
    > >>> the job of the camera.
    > >> No. No. No.
    > >>
    > >> Fast means larger aperture which leads to _faster_ shutter speed (the
    > >> setting, not the lag) due to reciprocity. That's where the 'fast' comes
    > >> from.
    > >>
    > >> (eg: 1/500 @ f/2.8 is faster than 1/125 @ f/5.6
    > >> The above is the same exposure, but 1/500 is faster. Get it?)
    > >>
    > >>
    > >> It has NEVER meant anything else.
    > >> =================================
    > >>
    > >>> And Larger Aperature means Better Glass and Better Glass means can
    > >>> FOCUS *faster* than small Aperature or slower lens.
    > >> Faster focus with faster lenses is simply because there is more light
    > >> (contrast) for the AF to work with so it can close the loop quicker.

    > >
    > > So, does it mean some top-of-the-line-lens (we are looking at $500-10000+
    > > lens) f4 and f5 lens are Slow Lens?. Because even they are the most
    > > expensive lens but they are F4 and F5 lenses.

    >
    > _Comparatively_ slower, yes indeed, but not the most expensive in many
    > cases.
    >
    > The Canon 300 f/4 is $1,200 but the
    > Canon 300 f/2.8 is over $4,000.
    >
    > The f/2.8 is almost 4x more expensive to be 1 stop faster.
    >
    > The real point is that the longer the focal length, the more expensive
    > it is to make a lens faster as the lens elements get larger.
    >
    > This is why many photographers refer to the lens as "glass". They are
    > talking about the whole lens (lens barrel and lens elements).


    You know, everyone know, and I know the F2.8 is more expensive and better
    in low-light than the F4. But we are talking about Fast Lens not larger
    aperature.

    Samething, Canon and other manufacture may be able to make a 800mm F2.8
    instead of 800mm F6.3 (or something like that). But the problem that in
    order to make f2.8 the 800mm should be lot larger, heavier so they make f4,
    f5.x, and f6.x instead.

    Yes, when talking about Fast Lens larger aperature is often part of it
    because they are capable to comparing to *most* (not all) smaller aperature.
    But FOCUS is still the main thing.

    Get ahold some Canon L lens like 400mm f4, 800mm f5.6 see how much Faster
    Focus comparing the cheapie F3.5, and even faster than *some* F2.8.
    Samething, most Canon f2.8 L lens often focus little faster than many third
    party f2.8 lens too.
     
    Joel, Feb 1, 2009
    #16
  17. Wayne R.

    OG Guest

    "Joel" <> wrote in message
    news:...
    > Alan Browne <> wrote:


    > Yes, when talking about Fast Lens larger aperature is often part of it
    > because they are capable to comparing to *most* (not all) smaller
    > aperature.
    > But FOCUS is still the main thing.


    Sorry Joel, but you are simply mistaken about that.
     
    OG, Feb 1, 2009
    #17
  18. "Joel" <> wrote in message
    news:...
    > "Norman Weaver" <> wrote:
    >
    >>
    >> "dadiOH" <> wrote in message
    >> news:ph5hl.616$2...
    >>
    >> > There are such things as constant aperture zoom lenses. They are
    >> > expensive. I have never seen one and have no idea how they overcome the
    >> > above but I suspect via magic :)

    >>
    >> I have a copy of Pentax's f3.5 35-105mm . I remember wondering how it
    >> worked
    >> much as you did. I ran through the zoom with the lens unmounted, and, as
    >> near as I can tell, the iris seems to simply close a little at the
    >> shorter
    >> end. The amount of speed lost would be minimal - probably only a fraction
    >> of
    >> a stop - so I have to assume that it's sacrificed in aid of easier or
    >> more
    >> consistent exposure calculation.
    >>
    >> Unless it's magic.;-)

    >
    > It sounds like a magical lens too me. How about comparing your Pentax
    > f3.5 35-105mm to either Canon 200-400L F4 or 800mm F5.x etc..
    >
    > The lens sport photographers use.


    An excellent idea! I've got nothing major planned for today. I'll rush out
    and buy a whole new camera system, just for you.

    Kidding aside, I would guess that any zoom would function much the same.
    Can't conceive of any other way of maintaining constant aperture.

    The 35-105 is actually a pretty fair lens, as MF zooms go. It's range is
    modest so manages to perform well enough at a reasonable price, and it's a
    nice range for a "walking around" lens in 35mm format, if a bit heavy.
     
    Norman Weaver, Feb 1, 2009
    #18
  19. Wayne R.

    Robert Coe Guest

    On Sun, 01 Feb 2009 11:03:41 -0500, Alan Browne
    <> wrote:
    : The Canon 300 f/4 is $1,200 but the
    : Canon 300 f/2.8 is over $4,000.
    :
    : The f/2.8 is almost 4x more expensive to be 1 stop faster.
    :
    : The real point is that the longer the focal length, the more expensive
    : it is to make a lens faster as the lens elements get larger.
    :
    : This is why many photographers refer to the lens as "glass". They are
    : talking about the whole lens (lens barrel and lens elements).

    Well, actually they're talking about the lens elements. The barrel, I think
    it's safe to say, is almost never made of glass. ;^)

    It does, of course, make some sense to ignore the barrel in such cases. Unless
    it can't manage to hold the elements in place, the characteristics of the
    barrel are nearly irrelevant. (Not totally irrelevant, however. Presumably
    Canon makes their larger lenses white because they're concerned that thermal
    expansion of the barrel might have optical consequences.)

    Bob
     
    Robert Coe, Feb 1, 2009
    #19
  20. Wayne R.

    Robert Coe Guest

    On Sun, 01 Feb 2009 11:20:46 -0600, Joel <> wrote:
    : Alan Browne <> wrote:
    :
    : > Joel wrote:
    : > > Alan Browne <> wrote:
    : > >
    : > >> Joel wrote:
    : > >>> Alan Browne <> wrote:
    : > >>>
    : > >>>> Joel wrote:
    : > >>>> It principally and classically means the aperture.
    : > >>>>
    : > >>>> The word "fast" comes as a consequence of shutter speed.
    : > >>>>
    : > >>>> The higher quality of material used contributes to sharpness, but
    : > >>>> so does the critical lens shape, assembly design and manufacturing.
    : > >>>>
    : > >>>>
    : > >>>> You're the one who put the "=" sign.
    : > >>> Nope! Fast Lens really mean Fast Focus *not* shuttle speed which is
    : > >>> the job of the camera.
    : > >> No. No. No.
    : > >>
    : > >> Fast means larger aperture which leads to _faster_ shutter speed (the
    : > >> setting, not the lag) due to reciprocity. That's where the 'fast' comes
    : > >> from.
    : > >>
    : > >> (eg: 1/500 @ f/2.8 is faster than 1/125 @ f/5.6
    : > >> The above is the same exposure, but 1/500 is faster. Get it?)
    : > >>
    : > >>
    : > >> It has NEVER meant anything else.
    : > >> =================================
    : > >>
    : > >>> And Larger Aperature means Better Glass and Better Glass means can
    : > >>> FOCUS *faster* than small Aperature or slower lens.
    : > >> Faster focus with faster lenses is simply because there is more light
    : > >> (contrast) for the AF to work with so it can close the loop quicker.
    : > >
    : > > So, does it mean some top-of-the-line-lens (we are looking at $500-10000+
    : > > lens) f4 and f5 lens are Slow Lens?. Because even they are the most
    : > > expensive lens but they are F4 and F5 lenses.
    : >
    : > _Comparatively_ slower, yes indeed, but not the most expensive in many
    : > cases.
    : >
    : > The Canon 300 f/4 is $1,200 but the
    : > Canon 300 f/2.8 is over $4,000.
    : >
    : > The f/2.8 is almost 4x more expensive to be 1 stop faster.
    : >
    : > The real point is that the longer the focal length, the more expensive
    : > it is to make a lens faster as the lens elements get larger.
    : >
    : > This is why many photographers refer to the lens as "glass". They are
    : > talking about the whole lens (lens barrel and lens elements).
    :
    : You know, everyone know, and I know the F2.8 is more expensive and
    : better in low-light than the F4. But we are talking about Fast Lens not
    : larger aperature.

    Joel, you should never have embarked on this argument.

    : Samething, Canon and other manufacture may be able to make a 800mm F2.8
    : instead of 800mm F6.3 (or something like that). But the problem that in
    : order to make f2.8 the 800mm should be lot larger, heavier so they make f4,
    : f5.x, and f6.x instead.
    :
    : Yes, when talking about Fast Lens larger aperature is often part of it
    : because they are capable to comparing to *most* (not all) smaller aperature.
    : But FOCUS is still the main thing.

    Get a grip, man! You're just digging the hole deeper. Now I'm the first to
    admit that your English is far better than my Chinese, or French, or whatever
    your first language is. But believe me when I tell you that it isn't good
    enough to sustain your claims in this discussion. Give it up before you make a
    total ass of yourself.

    : Get ahold some Canon L lens like 400mm f4, 800mm f5.6 see how much
    : Faster Focus comparing the cheapie F3.5, and even faster than *some* F2.8.
    : Samething, most Canon f2.8 L lens often focus little faster than many third
    : party f2.8 lens too.

    That is gibberish. Others will tell you so, even less politely. You ask for
    it; you're probably gonna get it.

    Bob
     
    Robert Coe, Feb 1, 2009
    #20
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