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  1. #11

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    BTL metering will compensate. What screws you up is if you use a hand meter or change focal length without a change in marked aperture. I don`t use them any more for that reason except for Nikon DX.

  2. #12

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    i would say that setting the camera to f8 then zooming in the aperture would still be f8 . maybe f8 wasnt a good example to use . now if you had said starting at the widest aperture for a given lens , lets use a 70 - 300 f4 - f5.6 zoom ., if you started off at 70mm and f4 then zoomed in , at a certain focal lenth the apeture would change and by the time you got to 300mm you would be at f 5.6 . even at f8 on this lens the aperture would stay the same throughout the entire focal range .
    nikon with above lens 70mm f4
    100mm f4.2
    135mm f4.5
    200mm ff5.0
    300mm f5.6 ( roughly )

  3. #13

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    what you would have to watch out for is if you are using an in between focal length , actual f stop might be a bit hit/n/miss

  4. #14
    Ed Sukach's Avatar
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    What happens to the numerical value of the f/stop depends om the placement of the aperture itself - the iris diaphragm. In a "constant aperture" system, the diaphragm is stationary - it will not move with the lens elements. If the diaphragm moves forward and back, the f/stop value will change accordingly.

    Remember the formula for f/stop:

    f/ = focal length (distance from diaphragm to film plane) / actual diaphragm diameter.

    As an example:

    Distance for diaphragm to film plane = 50mm
    Diaphragm aperture diameter = 25mm

    f/stop = 50(mm) / 25(mm) = f/2

    The placement of the diaphragm in a "zoom" system, is NOT universal; in some systems it may move more than in others - and I can't think of any way to determine where it is, other than referring to the design itself - or - (shudder, shudder) disassembling the lens and making many measurements....
    Carpe erratum!!

    Ed Sukach, FFP.

  5. #15

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    The answer is 'it depends'. If you're setting aperture from the aperture ring, yes it does vary with length as the aperture ring's settings are only accurate at the wide end of the zoom. With a f4-5.6 lens, setting f8 on the aperture ring will give you f8 at the wide end and f11 at the long end. In-camera metering and TTL flash handle this nicely, handheld metering for flash or ambient will have issues.

    If the body is setting aperture, it may or it may not, depending on the body (and that body's configuration, as some can be set to do either). The camera will most likely tell you the actual aperture though, as long as the lens and camera communicate electronically (exceptions include variable-aperture Pentax KA mount zooms, which can only tell the body the absolute max aperture, not the apertures through the zoom range)

  6. #16
    Michel Hardy-Vallée's Avatar
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    OK, I got my answer in person: using a Nikon FE body and a 28-80 f/3.5-5.6 D zoom, I can confirm that regardless of the f/stop set on the lens, zooming will change the effective aperture of the zoom.
    Using film since before it was hip.


    "One of the most singular characters of the hyposulphites, is the property their solutions possess of dissolving muriate of silver and retaining it in considerable quantity in permanent solution" — Sir John Frederick William Herschel, "On the Hyposulphurous Acid and its Compounds." The Edinburgh Philosophical Journal, Vol. 1 (8 Jan. 1819): 8-29. p. 11

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  7. #17

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    In your case that you using a Nikon FE then yes. The aperture changes as you zoom at all aperture. If you use the built in TTL meter then the meter does compensate for this but the aperture does change as you zoom.
    On the other hand if you use the same lens on a newer camera like an F5 or F100 and you set the lens at mininum aperture and then selecting the aperture via the sub command dial then the aperture won't change unless you set it near maximum or minimum aperture.

  8. #18
    Michel Hardy-Vallée's Avatar
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    Quote Originally Posted by Chan Tran View Post
    In your case that you using a Nikon FE then yes. The aperture changes as you zoom at all aperture. If you use the built in TTL meter then the meter does compensate for this but the aperture does change as you zoom.
    On the other hand if you use the same lens on a newer camera like an F5 or F100 and you set the lens at mininum aperture and then selecting the aperture via the sub command dial then the aperture won't change unless you set it near maximum or minimum aperture.
    Interesting, it looks like an offshoot of the shutter-priority mechanism developed for the FA. I've always been amazed that AI lenses had a provision for adjusting aperture from the body.
    Using film since before it was hip.


    "One of the most singular characters of the hyposulphites, is the property their solutions possess of dissolving muriate of silver and retaining it in considerable quantity in permanent solution" — Sir John Frederick William Herschel, "On the Hyposulphurous Acid and its Compounds." The Edinburgh Philosophical Journal, Vol. 1 (8 Jan. 1819): 8-29. p. 11

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