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Thread: Apature

  1. #81
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    Quote Originally Posted by Razr View Post
    If you read your own definition, it is not correct: Av mode means the aperture is locked on a given f/stop while the shutter is used to balance the exposure, as per Wikipedia (or any other resource)

    ---snip---

    Got it?
    Yes, I got it now. Let's look at Wikipedia
    The maximum aperture for a zoom lens may be same for all focal lengths, but it is more common that the maximum aperture is greater at the wide-angle end than at the telephoto end of the zoom range. For example, a 100 mm to 400 mm lens may have a maximum aperture of 4.0 at the 100 mm end but only 5.6 at the 400 mm end of the zoom range.
    I certainly got that a zoom lens may have a different max aperture at the short and long ends.

    Let's look at another resource, say the manufacturer of your 4/3rds cameras of choice(Olympus):
    Olympus/Zuiko makes some variable max-aperture zoom lenses for their 4/3rds cameras. I especially like how they have DOF values on their website for their lenses.

    http://www.olympusamerica.com/cpg_se...8-35/index.asp

    http://www.olympusamerica.com/cpg_se...8-35/index.asp

    http://www.olympusamerica.com/cpg_se...8-35/index.asp

    What I can't understand is why there is no DOF info on these lenses at the middle range or long end for say f/2.8 and no DOF info on these lenses at the long end for say f/3.2. Could it possibly be because Olympus/Zuiko does not know how to "lock" the aperture at f/2.8 in Av mode for the entire zoom range, or because zooming these lenses causes the max aperture to change from f/2.8 to f/3.5 as it says in their literature/website. Hmmmmmmmmm?

    edit: I hope that this is not just a limitation of the 4/3rds format.

    Ray.
    Last edited by Ray Schnoor; 10-25-2007 at 06:44 AM.

  2. #82
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    Quote Originally Posted by Razr View Post
    It is you who are misinformed about what Av mode is and does-see below. ?? You cannot set the aperture (on one f/stop in Av mode) and then say: " allows you to be able to change your aperture". That makes no sense. You cannot set a camera one one f/stop in Av mode, then "allow it to change". If you read your own definition, it is not correct: Av mode means the aperture is locked on a given f/stop while the shutter is used to balance the exposure, as per Wikipedia (or any other resource)
    Do you and the others now get the fact that the aperture is frozen on one f/stop in Av mode? Get it?

    It is not me who has been struggling with what happens when a person chooses Av mode: it is you and they. BINGO! Which at the same time, tells you why Av mode holds-freezes-locks the aperture on one f/stop (my original thesis), regardless of why the photographer chose or chooses to use Av mode.
    Got it?
    Razr, you obviously don't have a clue.
    The Wikipedia article you link to does not support your case. It says that in apperture priority mode you select the apperture and the camera calculates the shutterspeed. That's all. There's really nothing in that article about locking appertures into place.

    The only thing which is locked when using the aperture priority mode are the apperture blades if and only if you select the maximum aperture.
    If you don't select the maximum apperture even the apperture blades change as you zoom in (they will go wider).
    However, due to zooming in, the relative apperture gets smaller due to the increase in focal length. Thus there is less light that will reach the sensor which is why the f-stop gets larger.

    I guess in the next thread you will start claiming that if you twist the zoom ring of a lens far enough, you can push a 70-300 up to 400mm.... And that with a constant apperture of f/4.... Simply amazing
    Nikon D-50
    // Nikkor 70-300 f/4-5.6 VR // Nikkor 50 mm f/1.8
    // Sigma 17-70 f/2.8-4.5 ...// Nikon SB-600
    // Sigma 10-20 f/4-5.6......// Nikon Series E 135 mm f/2.8
    // Kiron 105 f/2.8 Macro....// Manfrotto 190XPROB + 488RC4
    // Nikkor 35 f/1.8..........// Sigma 500 mm f/8

    My website: http://www.dennisdolkens.nl

  3. #83
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    Quote Originally Posted by fionndruinne View Post
    All Razr needs to do is pop a variable max-aperture on a body and try it, as I suggested.
    I did that back in 1983 with my Pentax Super Program and Vivitar Series 1 (67mm) one-button Macro f/3.5 constant aperture lens.
    Man, if only a 17-70mm which was really f/2.8 across the full range cost as little as that Sigma does...
    Too bad you haven't tried or didn't know you could do just that: make your lens an f/2.8 (or whatever) constant aperture lens.
    Try it: set your camera body on Av and f/2.8 then zoom.
    Youll see the shutter speed (only) change as more or less light enters the lens.
    Go ahead-give it a go.

  4. #84
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    To have this make sense, you need to remember that the aperature number is a ratio between the size of the opening in the blades, and the mm length of the lens.

    In a lens with constant aperture, the aperture blades widen as the lens zooms to keep that ratio the same. Its mechanically driven by the zoom twist. In a lens with a variable max aperture, the blades generally open too as the lens zooms, but not enough to completely compensate for the increase in length. So the max aperture number changes.
    My best pics on Flickr

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    Gear: Canon 60D, Sigma 18-50 f2.8 EX DC Macro, Sigma 50-150 f2.8 EX DC II, Canon 50 f1.8, Sigma 10-20 f4-5.6 EX DC, Sigma 120-400 DG OS. 1 430EX, 1 430EXII, 1 580EXII, ST-E2, Manfrotto 190XPROB (soon to be replaced by the carbon version)
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  5. #85
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    Quote Originally Posted by Razr View Post
    I did that back in 1983 with my Pentax Super Program and Vivitar Series 1 (67mm) one-button Macro f/3.5 constant aperture lens. Too bad you haven't tried or didn't know you could do just that: make your lens an f/2.8 (or whatever) constant aperture lens.
    Try it: set your camera body on Av and f/2.8 then zoom.
    Youll see the shutter speed (only) change as more or less light enters the lens.
    Go ahead-give it a go.
    Actually, you will see that it reaches f/3.2 before you reach 20mm.
    And believe me, I posses that lens and I tried it (the reason I did that was to see for what length it is actually f/2.8, not to test the obvious).

    And please cut the crap about your experiences with cameras back in 1983. If you were really a professional photographer back then, you would have realized that everything you said in this thread is complete nonsense.
    Nikon D-50
    // Nikkor 70-300 f/4-5.6 VR // Nikkor 50 mm f/1.8
    // Sigma 17-70 f/2.8-4.5 ...// Nikon SB-600
    // Sigma 10-20 f/4-5.6......// Nikon Series E 135 mm f/2.8
    // Kiron 105 f/2.8 Macro....// Manfrotto 190XPROB + 488RC4
    // Nikkor 35 f/1.8..........// Sigma 500 mm f/8

    My website: http://www.dennisdolkens.nl

  6. #86
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    Ray:
    Yes, I got it now. Let's look at Wikipedia

    Quote:
    The maximum aperture for a zoom lens may be same for all focal lengths,
    "May be the same for all focal lenths" being the operative phrasing, the "may be" being when the lens is operated in Av. mode.
    but it is more common that the maximum aperture is greater at the wide-angle end than at the telephoto end of the zoom range. For example, a 100 mm to 400 mm lens may have a maximum aperture of 4.0 at the 100 mm end but only 5.6 at the 400 mm end of the zoom range.
    Which is absolutely true in Program mode, not so in Av. since the aperture can be set at f/4 in Av mode and at 400m, would still be f/4.
    I certainly got that a zoom lens may have a different max aperture at the short and long ends.
    Let's look at another resource, say the manufacturer of your 4/3rds cameras of choice(Olympus):
    Olympus/Zuiko makes some variable max-aperture zoom lenses for their 4/3rds cameras. I especially like how they have DOF values on their website for their lenses.

    http://www.olympusamerica.com/cpg_se...8-35/index.asp

    http://www.olympusamerica.com/cpg_se...8-35/index.asp

    http://www.olympusamerica.com/cpg_se...8-35/index.asp

    What I can't understand is why there is no DOF info on these lenses at the middle range or long end for say f/2.8
    Because they didn't test (never test) the lenses using f/2.8 in Av mode?
    and no DOF info on these lenses at the long end for say f/3.2.
    ?? what does f/3.2 have to do with it?
    Could it possibly be because Olympus/Zuiko does not know how to "lock" the aperture at f/2.8 in Av mode for the entire zoom range, or because zooming these lenses causes the max aperture to change from f/2.8 to f/3.5 as it says in their literature/website. Hmmmmmmmmm?

    Ray.
    As I noted before and even with OLYMPUS, all such "tests" are conducted in "P" mode, not Av. And the aperture (no matter which is chosen) is locked in Av.

  7. #87
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    Quote Originally Posted by Crazr
    Because they didn't test (never test) the lenses using f/2.8 in Av mode?
    Right, they make a lens that actually has a wider apperture than they claim and show in such online resources

    Now that is some good marketing

    If the 17-70 f/2.8-4.5 could do f/2.8 at 70 they would call it a 17-70 f/2.8. No question about it .
    Nikon D-50
    // Nikkor 70-300 f/4-5.6 VR // Nikkor 50 mm f/1.8
    // Sigma 17-70 f/2.8-4.5 ...// Nikon SB-600
    // Sigma 10-20 f/4-5.6......// Nikon Series E 135 mm f/2.8
    // Kiron 105 f/2.8 Macro....// Manfrotto 190XPROB + 488RC4
    // Nikkor 35 f/1.8..........// Sigma 500 mm f/8

    My website: http://www.dennisdolkens.nl

  8. #88
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    Quote Originally Posted by achuang View Post
    Say what you want about me being wrong Razr, but everyone else who has read what i posted knows it is correct. And prospero's post was a more detailed and very well written explanation of aperture size. What you're saying is that every person who has posted is wrong and that you're the only one who is right.
    My last post in this thread. Here are 2 links, have a read and learn to admit when you're wrong.
    Aperture priority
    From Wikipedia, the free encyclopedia

    Aperture priority, often abbreviated Av or A on a camera dial, is a setting on some cameras that allows the user to choose an aperture while the camera selects a shutter speed to match. The camera will ensure proper exposure. This is different from manual mode, where the user must decide both values, shutter priority where the user picks a shutter speed with the camera selecting the aperture to match, or program mode where the camera selects both.

    The main purpose of using aperture-priority mode is to control the depth of field. Aperture priority is useful in landscape photography, where a narrow aperture is necessary if objects in foreground, middle distance, and background are all to be rendered crisply, while shutter speed is often immaterial. It also finds use in portrait photography, where a wide aperture is desired to throw the background out of focus and make it less distracting.

    Another common use of aperture priority mode is to suggest how the camera should decide a shutter speed, without risking a poor exposure. In landscape photography a user would select a small aperture when photographing a waterfall, hoping to allow the water to blur through the frame. When shooting a portrait in dim lighting, the photographer might choose to open the lens to its maximum aperture in hopes of getting enough light for a good exposure.

    In addition, aperture priority mode allows the photographer to force the camera to operate the lens at its optimum apertures. . Commonly, lenses provide greatest resolving power with a relatively medium-sized aperture.
    "Ta-da"!
    Of course you all may have missed the most important (for this discussion)part of the Wikipedia statement so I'll repeat:
    "force the camera to operate the lens at its optimum apertures, the operative phrase which, in laymen's terms, means forcing the camera to use the aperture of choice and/or any other "optimum aperture": my original thesis;
    thanks Wikipedia.

  9. #89
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    Quote Originally Posted by Razr View Post
    "May be the same for all focal lenths" being the operative phrasing, the "may be" being when the lens is operated in Av. mode..
    Wrong. "May be the same for all focal lengths" only refers to constant max-aperture lenses vs variable max-aperture lenses such as these 2 examples:
    http://www.sigmaphoto.com/lenses/len...25&navigator=6
    http://www.sigmaphoto.com/lenses/len...20&navigator=6
    Quote Originally Posted by Ray Schnoor View Post
    Let's look at another resource, say the manufacturer of your 4/3rds cameras of choice(Olympus):
    Olympus/Zuiko makes some variable max-aperture zoom lenses for their 4/3rds cameras. I especially like how they have DOF values on their website for their lenses.

    http://www.olympusamerica.com/cpg_se...8-35/index.asp

    http://www.olympusamerica.com/cpg_se...8-35/index.asp

    http://www.olympusamerica.com/cpg_se...8-35/index.asp

    What I can't understand is why there is no DOF info on these lenses at the middle range or long end for say f/2.8 and no DOF info on these lenses at the long end for say f/3.2. Could it possibly be because Olympus/Zuiko does not know how to "lock" the aperture at f/2.8 in Av mode for the entire zoom range, or because zooming these lenses causes the max aperture to change from f/2.8 to f/3.5 as it says in their literature/website. Hmmmmmmmmm?
    Quote Originally Posted by Razr View Post
    Because they didn't test (never test) the lenses using f/2.8 in Av mode? As I noted before and even with OLYMPUS, all such "tests" are conducted in "P" mode, not Av. And the aperture (no matter which is chosen) is locked in Av.
    Wrong again. I don't think I have ever seen any camera in "P" mode choose the minimum aperture possible on a lens. I guess maybe if they are taking a direct shot of the sun, maybe. Do you suppose they just sit there fiddling with the light source until they get at those f/#s. No, they set the f/#s in aperture priority mode to save time. Duh....

    edit: Actually, I doubt they even perform these tests. They probably just do the math on the depth of field with a certain focal length/aperture value and put down the values. This would be even more curious why they do not include the DOF values for f/2.8 at medium and long ends of the zoom range.

    And I included the f/3.2 comment because that is the max aperture value at the medium range of the zoom, at least according to their website.

    Another quote from their wetsite:"Maximum Aperture f 2.8 Wide - f 3.5 Telephoto"

    Ray.
    Last edited by Ray Schnoor; 10-25-2007 at 07:25 AM.

  10. #90
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    Quote Originally Posted by fionndruinne View Post
    That's what I was saying. Apparently Razr keeps his cameras locked in a dust-proof hermetically sealed location to avoid descending to our level of brute amateurishness by actually putting a grimy paw on the shutter.
    "Grimy paw"?

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