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  1. #11

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    As Rol Lei Nut mentioned, many zooms' aperture vary with zoom setting. So it may be, say, f/4 at the wide end, but can well be a stop or more slower at the long end.
    The markings on the aperture scale however will not change, and you will get errors if transferring settings from a separate meter to the lens.
    So make sure the zoom has a fixed speed, or else it cannot be used (or only with difficulty) when you measure light using a separate, non-TTL meter.

  2. #12

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    Yes, what Q.G said.

    However, it's really not that difficult. Your zooms will be marked with at least two apertures... one for widest FL and the other for the longest. Let's just say the difference is 1.5 f/stops. Zoomed 1/3 out open 1/2 f/stop... 2/3 out... 1 f/stop... all the way out... 1.5 f/stops. In fact, there may be markings on the barrel in several places to give you the proper correction factor. You just need to remember to make the correction. And remember too that it won't be as accurate as using TTL metering (because of the varying aperture).

  3. #13
    T42
    T42 is offline

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    Quote Originally Posted by Rol_Lei Nut View Post
    Better example, if you photograph the cat sitting on a pile of coal in a snowy landscape:

    With the 200mm, you might only frame the cat itself (presumably close to neutral grey in tone) and so get a "correct" exposure.
    With the 50mm (if you are now taking in the whole scene), you might be getting more or less of the snow or coal in the image, and the camera's meter might be "fooled" by the lighter or darker objects one way or another.
    But with both lenses, if you are careful to only meter the cat, no exposure compensation is needed (the meter should give the same results).

    Also, if the zoom's aperture varies with its focal length, you need to take that into account if using a hand-held meter.
    I think Rol_Lei Nut said it best. I would just add that if one is to trust the meter alone, then the "ideal cat" would be average/18%/Zone-V in reflectance. A black cat or white cat would have some of the same problems as would the coal or snow. IMO, any metering system requires some interpretation to arrive at the desired exposure for each imagemaking case. That comes with experience.

    I have come to trust incident metering more than the other methods. Many, including Ansel Adams, prefer/preferred spot metering. What I trust the least are the "smart" metering algorithms which have minds of their own. I can't tell what they are thinking, and so I cannot as easily predict or compensate for when they get things wrong.

    A good reflective/incident ambient/flash hand meter is a good addition to one's kit, in my opinion. I have been using the Sekonic L308B for a few years, and I like it very much. It runs on a single AA cell. If one is on a tight budget, a Kodak gray card can give "incident" type readings while using a reflective meter, hand-held or in-camera.

    Also, there is a direct relationship between the reflectance of the palm or back of your hand and what a gray card will yield. One should know that difference. Then one always has a way to get a reference meter reading that can be trusted as a starting point. The back of my hand is one stop brighter than a gray card. Knowing this, I can read from it, open a stop, and know that I have an approximation of what an incident or gray card reading would have provided.
    Last edited by T42; 02-22-2010 at 01:21 PM. Click to view previous post history. Reason: typos
    Henry
    A Certified Dinosaur
    Nikons F, F2, D700, Leica M3, & Kiev 4a

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