Fixed Aperture Pentax Zoom

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

  1. Wayne R.

    Wayne R. Guest

    Wayne R., Feb 1, 2009
    #21
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  2. Wayne R.

    Joel Guest

    GLASS is glass or the marterial the glass made of. Sa,e with Fast Lens
    doesn't mean larger aperature or faster shutter speed.
     
    Joel, Feb 1, 2009
    #22
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  3. Wayne R.

    Joel Guest

    Thanks! and I will buy you 3-5 magical f3.5 35-105mm lens to return your
    If you mean the lens moving IN and OUT then you are right they are very
    similar to each other. But if you are talking about Quality and Focus then
    I afraid there will be a huge difference.
    If you are talking about ZOOM range then I agree 35-105 is a very good
    range. But I am talking about the QUALITY and what the 35-105 f3.5 is
    capable of.

    No kidding, if any of your friend has something like Canon 70-200L,
    100-400L, 200-400L, 500L, 800L etc. then just ask him/her to lets you give
    it a try.

    - FOCUS is what you want to pay closer attention.

    - Image Quality you should be able to find tons of them on the web. You may
    not be able to find the original, but it's possible. And study the XRIF to
    see the setting.
     
    Joel, Feb 1, 2009
    #23
  4. No, what I mean is the method for maintaining constant maximum aperture
    throughout the zoom's range - not zoom function, not resolution, not
    distortion, not autofocus performance, and not any other thing you care to
    bring up.
     
    Norman Weaver, Feb 2, 2009
    #24
  5. Wayne R.

    Joel Guest

    I read and heard what you said, but I can only agree with you at some
    degree not the whole point.

    - Yes, Good Glass does mean the whole unit, but also to understand the unit
    with *real* Good Glass the material the glass's made of.

    - Yes, Fast Lens does mean the whole unit with glass is good enough to
    capture image at lower-light larger aperature, but doesn't really mean Fast
    Lens when talking about the SPEED (Faster Focus).

    Samething, Yes "I am full" does mean I have eaten enough food to fill my
    stomatch, but when it comes to "do you enjoy what you ate" then it will go
    to the point "what you ate" etc..

    Samething, I have pointed out the 400L f4 and 800L f5.6 those have much
    smaller aperature, but you seem to ignore them etc..
    Nope! mine only sink on real thing.
     
    Joel, Feb 2, 2009
    #25
  6. Wayne R.

    Joel Guest

    Of course I knew you didn't mean the mechanical part (kinda kidding) ,
    that was why I mentioned about the IQ (Image Quality) and FF (Fast Focus).
    And as I have mentioned in the very first message that Fast Lens requires

    - Good Glass (marterial glass made of) to see clearer image in order to
    capture better image at poorer condition.

    As I have mentioned using F2.8 lens doesn't mean to shoot at f2.8 but
    because the quality of the Glass is good enough to capture acceptable image
    at f2.8

    Besides some wide angle lens and special designed lens (like long zoom
    with Fast Focus) for fast action sport, most if not all regular f3.5 or f4
    is not only slow, but often blur/soft comparing to the special design like
    Canon 100-400L f4, or 800L f5.6 etc.

    Yes, you can get pretty sharp capture using cheapie lens, but it will have
    to meet several requirements like.

    a. shooting at smaller aperature

    b. Plenty of light in order to shoot at smaller aperature. Of course
    someone may argue using tripod, but I don't wanna go that far, so I just
    give the general information instead.

    c. And it may take longer time to FOCUS (or we call HUNTING). Of course
    someone may argue that if it can't auto-focus then we can use MANUAL, but
    again that ain't go that far either.

    - And as I have mentioned, if you have a friend with some special design
    lens (Fast Lens), or just go to a local camera store to try some top-notch
    lens to find out that the Focus is so fast almost like real-time. Or it's
    almost in focus even when you move slowly, and in focus immediately ready to
    press the shutter button when you move to the subject.

    Or with slower lens, or even some f2.8 or larger (we often call them Fast
    Lens or Good Glass because they are fast and better glass when comparing to
    regular lens) you may find some may take few seconds to focus (Hunting), and
    quite afew may start hunting with a small movement. Or you may find the
    focus keep changing In/Out Of Focus (OOF).

    That's kinda of good lens I am talking about, not saying if the lens is
    capable of capturing sharp image or not.
     
    Joel, Feb 2, 2009
    #26
  7. Wayne R.

    Wayne R. Guest

    Everyone's clear on what you're talking about. It's just that your
    name for it means something else to everyone else.

    In the continuum of similar lenses, fast lenses allow more light
    through than their peers - that's the way everyone else uses the term,
    and that use goes back to well before auto-anything.

    Feel free to dedicate the 'speed' concept to autofocus but also
    understand that you'll be in a distinct minority.
     
    Wayne R., Feb 2, 2009
    #27
  8. Wayne R.

    OG Guest

    I think he's stopped arguing seriously and is just trolling now.
     
    OG, Feb 2, 2009
    #28
  9. Wayne R.

    Joel Guest

    I actually don't really care what Wayne R. may say cuz you may want to
    believe what Wayne say but not me.
    It either you try to ignore my point or whatever reason.

    -You just can't use dirty glass or cheap plastic on F2.8 or F1.0 which just
    won't work.

    - The reason why most cheapie lens is slow Focus, Blurry, Soft, can't handle
    poor lighting situation etc.. not because they have different designed, but
    because the meterial use to make the GLASS is a cheap material.

    - Or you just cover the f1 lens with cheapie dirty filter to see if it still
    work as good as the original f1.0. I am talking about the GLASS now.
     
    Joel, Feb 3, 2009
    #29
  10. Wayne R.

    Joel Guest

    Thanks for making my point, now go get your point then continue to talk
    <bg>
     
    Joel, Feb 3, 2009
    #30
  11. Wayne R.

    Peter Guest


    If the barrel has the same coefficient of expansion as the glass, why would
    it need to be white? Or, is that marketing hype

    OTOH Why wouldn't the opposite be true when dong cold weather shooting?
     
    Peter, Feb 4, 2009
    #31
  12. Wayne R.

    Peter Guest

    I knew it wouldn't be the last time you said that. <g>

    (see you prior response)
     
    Peter, Feb 4, 2009
    #32
  13. Wayne R.

    Wayne R. Guest

    Sunshine on one side of the barrel while the other side is in shadow?
     
    Wayne R., Feb 4, 2009
    #33
  14. Wayne R.

    Robert Coe Guest

    : : > On Sun, 01 Feb 2009 11:03:41 -0500, Alan Browne
    : > : 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.)
    :
    :
    : If the barrel has the same coefficient of expansion as the glass,

    It doesn't ...

    : why would it need to be white? Or, is that marketing hype

    .... But even if it did, a lens that has undergone thermal expansion, even
    without distortion, is unlike to faithfully preserve all its optical
    properties.

    : OTOH Why wouldn't the opposite be true when dong cold weather shooting?

    Maybe it *would* be better to use a black lens on a cold day, especially in
    the sun. But absorption of sunlight aside, a black lens loses heat faster
    through radiation than a white lens does. And in really cold weather, cameras
    already don't work all that well.

    Bob
     
    Robert Coe, Feb 6, 2009
    #34
  15. Wayne R.

    Peter Guest

    Not certain about that. Do you have any place I can see a comparison? My
    Chemical Rubber Handbook, 35th Edition, doesn't cover modern glass and
    composits. ( I used modifications 0f some of its foruulas to mix my own
    developing agents.

    That would apply to thermal contraction as well. I am not an optical
    physicist, but think that a quality lens design would be ideal at some
    median temperature. I think that any temperature varient would naturally
    cause some change in optical quality.
    I don't understand the physcal reason for your statement. I always thought
    that black tended to absorb radiant heat and white reflected radiant heat.
    that makes sense, but I am not really sure what you mean by not working
    that well.
     
    Peter, Feb 10, 2009
    #35
  16. Wayne R.

    Robert Coe Guest

    : : > On Wed, 4 Feb 2009 07:50:22 -0500, "Peter" <>
    : > wrote:
    : > : : > : > On Sun, 01 Feb 2009 11:03:41 -0500, Alan Browne
    : > : > : 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.)
    : > :
    : > :
    : > : If the barrel has the same coefficient of expansion as the glass,
    : >
    : > It doesn't ...
    :
    : Not certain about that. Do you have any place I can see a comparison? My
    : Chemical Rubber Handbook, 35th Edition, doesn't cover modern glass and
    : composits. ( I used modifications 0f some of its foruulas to mix my own
    : developing agents.

    I was assuming (probably erroneously) that the barrel would be steel or
    aluminum (i.e, some metal). Most metals are more subject to thermal expansion
    and contraction than glass is. My gut tells me that plastic is less subject to
    expansion than glass, but I don't know for sure.

    : > : why would it need to be white? Or, is that marketing hype
    : >
    : > ... But even if it did, a lens that has undergone thermal expansion, even
    : > without distortion, is unlike to faithfully preserve all its optical
    : > properties.
    :
    : That would apply to thermal contraction as well. I am not an optical
    : physicist, but think that a quality lens design would be ideal at some
    : median temperature. I think that any temperature varient would naturally
    : cause some change in optical quality.

    Yes, I think so too.

    : > : OTOH Why wouldn't the opposite be true when dong cold weather shooting?
    : >
    : > Maybe it *would* be better to use a black lens on a cold day, especially
    : > in
    : > the sun. But absorption of sunlight aside, a black lens loses heat faster
    : > through radiation than a white lens does.
    :
    : I don't understand the physcal reason for your statement. I always thought
    : that black tended to absorb radiant heat and white reflected radiant heat.

    What absorbs better also radiates better, for the same reason. Black objects
    absorb heat faster, but give it back faster.

    : >And in really cold weather, cameras already don't work all that well.
    : >
    : that makes sense, but I am not really sure what you mean by not working
    : that well.

    Most (all?) electronic devices work best at STP. If you look carefully at the
    specs for your digital camera, you'll see that there's a maximum and minimum
    temperature at which it's supposed to work correctly. The latter may be higher
    than you might have thought.

    Bob
     
    Robert Coe, Feb 12, 2009
    #36
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