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  1. #21

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    Just in case the web site I linked to disappears in the future.

    "Where the desired aperture is mechanically set via the aperture ring around the body of the lens … this info is then mechanically transferred to the camera body and then used in conjunction with the shutter speed / ISO setting / metering pattern, etc, to get to a meter reading.

    In this case, the variable aperture of a lens will show up during the entire aperture range. ie, f4 becomes f5.6 … f8 becomes f11 … f16 becomes f22 … as you zoom to the longer focal length. In this case you will see the meter reading in your camera change as you zoom in and out.

    Where the desired aperture is electronically set on the camera body via a thumbwheel … this info is then used to calculate the exposure and to set the lens to the specific aperture needed.

    In this case, for a variable aperture lens, the aperture will ONLY vary when the maximum aperture is set at the widest length, and you then zoom in. For any other aperture that you set via the camera thumbwheel, you will get the aperture you requested. ie, f3.5 will change to f4.5 .. but f5.6 will remain f5.6 … f8 will remain f8 … f11 will remain f11. Therefore you won’t see the exposure info change in the camera’s viewfinder, except if you zoomed from wide to tele at wide open aperture."


    Quote Originally Posted by Diapositivo View Post
    For what I understand, when using an external meter with a variable aperture zoom lens you normally worry only when using the lens at its maximum aperture. When using the other positions in your diaphragm ring, the f/number indicated remains the same regardless of the focal length.

    An example: sun high, bright day, front lit subject, you use the "sunny 16" rule, and decide for 1/250 @ f/11 with ISO 125.

    Your variable aperture zoom should give you f/11 at every focal length.

    That's because when you use the lens at a less-than-full-aperture, you cut away the geometric limit given by your front lens. Your front lens is larger than what is needed to give you f/11, at all focal length.

    In the case of the OP I am quite puzzled about what would happen with the second value, 5.6, supposing such a value exists on such a lens as a separate case from full aperture, but that would appear very strange to me.
    The most normal case is that the variable aperture lens has full aperture indicated as f/4-f/5.6 and the next aperture is straight f/8.
    In this case, f/8 is reliable at all focal length when using an external light meter.
    "There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).

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  2. #22

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    Quote Originally Posted by E. von Hoegh View Post
    And folks wonder why I don't use zooms, ever.
    I have no love for them either, especially after this, but I am stuck with it for now, unless someone wants to send me some nice AI Nikkor primes

  3. #23
    Chris Nielsen's Avatar
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    Interesting thread. The only zooms I have ever had are modern Nikkors and have CPUs in them so 5.6 is always 5.6 but 4 is not always 4. However if I get a variable aperture zoom for my OM2 I will be finding the same problem as the OP. Good to know if I ever put a variable aperture zoom on a meterless camera!

  4. #24
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    I had already read the quoted excerpt from the quoted link before writing my post.

    I wrote it because I am not convinced and wanted to inquiry the matter further.

    It could be that the quoted author infers what he writes because while zooming he sees a variation in the shutter speed chosen by the camera.

    This is natural, because the TTL light metering is normally performed at full aperture, where this behaviour cannot help manifesting itself.
    This is compensated by the TTL metering itself, as explained by Leigh B in post #15 above.

    The problem with mechanical-coupled diaphragm simulators possibly arises only at full aperture where, let's say, the simulator says f/4 but the lens only transmits f/5.6, but this is compensated by the TTL measuring which observes a fall in light and compensates with a slower shutter speed.

    If what I suspect is true, not just the zoom lens maintains f/8 at all focal length, but also there is no problem in mechanical diaphragm simulation as the mechanical simulator always says f/8. So the "variable aperture" could only manifest itself at full aperture, and not for other apertures, and the TTL metering works OK in all cases.

    The answer to my doubt can be given by performing the same kind of exposure reading while zooming activity, but with the lens stopped-down.

    I will try to do some test tomorrow (now it's night, and I have a headache as well). But I only have a "not so variable aperture" zoom.

    So I ask anybody reading this thread and having a variable aperture zoom to perform the following test:

    Put the zoom at its minimum focal length.
    Put the diaphragm ring to f/11.
    Stop-down the diaphragm.
    Read the metered exposure.
    Now, while keeping the diaphragm stopped-down, zoom to maximum tele position and observe if the exposure changes.

    I suspect that the suggested shutter time does not change (meaningfully).
    Fabrizio Ruggeri fine art photography site: http://fabrizio-ruggeri.artistwebsites.com
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  5. #25

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    Quote Originally Posted by Chris Nielsen View Post
    Interesting thread. The only zooms I have ever had are modern Nikkors and have CPUs in them so 5.6 is always 5.6 but 4 is not always 4.
    Same here, except the minimum aperture is variable too. Try it; the further you zoom in, the further you can stop down. I don't understand the physics, but I think Chan Tran is right regarding electronic cameras.

    At any rate nwilkins, I'd humbly suggest you use the TTL meter on the camera for best results. Regarding AI prime lenses, there are tons to be had for dirt cheap. And you can even use autofocus lenses on your camera as long as they have aperture rings.

    Some of the most inexpensive (yet optically fine) Nikkors include the 28mm f/3.5, 35mm f/2.8, and 135mm f/3.5. Add the 50mm of your choice and you are set for anything.

  6. #26

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    I have a couple of Tokina variable aperture zooms that I bought new in about 1984. During this period, most consumer oriented 35mm SLRs had some kind of TTL metering as well as Auto exposure modes. These lenses both have two aperture index marks. The first mark in white indexes the aperture for the shortest focal length of the lens and the orange index mark indicates the aperture for the longest focal length. There is a one stop difference when zooming all the way from shortest to longest focal length.

    One lens is the Tokina SZ-X210 which is a 70-210mm lens with a variable aperture of f/4-5.6. So when you would use this lens at 70mm and f8 and the you zoom to 210mm you get an aperture of f11 if you don't change the aperture setting. This was a fairly common design for the mid 1980's. There were also zoom lenses that had constant apertures throughout the zoom range. These were generally built to a higher standard and sold for two or three times the amount each.
    Dave

    "She's always out making pictures, She's always out making scenes.
    She's always out the window, When it comes to making Dreams.

    It's all mixed up, It's all mixed up, It's all mixed up."

    From It's All Mixed Up by The Cars

  7. #27
    Diapositivo's Avatar
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    Mopar_guy, thanks for the clarification.

    As said, I have two zooms: one is a Minolta Rokkor MD 100-200/5.6 (fixed aperture). The other is a Minolta Rokkor MD 28-85/3.5-4.5 (variable aperture). It is interesting to know that while using an external lightmeter the actual aperture is actually 1/3 EV more when at 28mm and 1/3 EV less at 85mm than what is indicated, at any aperture. The difference is not dramatic but it must be there.

    A day spent without learning something is a wasted day
    Fabrizio Ruggeri fine art photography site: http://fabrizio-ruggeri.artistwebsites.com
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  8. #28

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    So, I did as you suggested and put my Zeiss Jena 28-210 f 3.8-5.6 on a Contax S2 (all manual).
    And, indeed a clear blue sky metered about 2 stops differently between 28mm and 210 mm.
    Not quite what you asked for, but the S2 would not meter at all with the depth of field button stopped down.
    So I tried the lens on a Contax 159 and it does read stopped down, which at 28mm was 3 stops less than wide open and 1 more stop less when zoomed. Not all perfectly consistent, but good enough for government.
    When you set the F stop on the manual camera, you are not so much setting an F stop as you are setting an aperture diameter, which the mechanical linkages stop down to, at exposure. The conversion of that aperture to an Fstop requires the assumption of a focal length of lens.
    The flip side of this is interesting as well. It means that at 200 mm I have lost 2 stops of speed if I want to maintain the same aperture.
    Thanks for asking the question
    "There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).

    Regards
    Bill

  9. #29

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    I can't say for all variable aperture zoom but I think they are similar. I have made a test with my Nikon 70-300mm f/4-5.6 IF-ED-D lens. I put this lens on a Nikon FM, set the focus at infinity, pointing the lens to my enlarger color head. I remove the color head from the enlarger and power it up putting in horizontally. With my dicrho DG head for the 4x5 enlarger I have about 6" circle of intense and quite even light area. I checked with a spot meter and there is less than 2/10 of a stop from center to the edge. I position the lens about 6" from this and this lighted area would completely cover the full frame. I removed the back of the camera and put the Minolta booster II unit with a film plane attachment and connect this to the Minolta flashmeter III. Zooming the lens at various aperture I can confirm that at all apertures there is about 1 stop of light loss from 70mm to 300mm. The drop in illumination seems to proportion to the amount of zoom setting although not exactly.
    When I mount this lens on the Nikon F5, set the aperture ring at minimum and set the aperture via the dial on the camera. The aperture stays constant if I set it to anything between f/5.6 and f/32. Aperture larger than f/5.6 is possible at the shorter end and smaller than f/32 is possible at the long end. I can't do the same at the film plane measurement with the meter on the F5.

  10. #30
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    On the aforementioned Tamron 70-210, which I have in front of me, there are two white lines between the focusing ring/dof scale and the aperture ring. When the lens is at 70mm, the thicker white line shows what the aperture is. At 210mm, the thin white line is the effective aperture. If you're shooting at f/8, set the ring to 5.6 when you're approaching 210mm. Meter reading should be the same with the ring at 5.6 and the lens zoomed out to 210 as it would be with the ring at 8 and the lens set at 70mm.

    Just verified this with my F FTn. At 70mm, f/11 gave me 1/8 second with ISO 100 film. At 210mm, f/8 gave me 1/8 second. When shooting at the intermediate settings, set the ring between numbers to get correct exposure.

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