Hand held meter and lens focal length.

Discussion in '35mm Cameras and Accessories' started by Mike Kennedy, Feb 20, 2010.

  1. Mike Kennedy

    Mike Kennedy Member

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    I'll be testing the Minolta SRT-201 today.There are 2 lenses that I will use: #1.50mm 1.7 #2.70-200.
    Will I have to adjust the metering to compensate for the different glass?

    Thanks
     
  2. Cainquixote

    Cainquixote Member

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    what will you be shooting?

    my short answer is no. If you were photographing a cat and the meter says f5.6 at 1/125 it will be the same for a 200mm shot as it would be for a 50mm shot.

    The problem is if you shoot the 50mm at the same distance that you shoot it at 200mm the field of view will change. The shot at 50mm will have a bigger field of view and potentially have more variance in the highlight and shadow areas.

    So yes you might have to adjust the exposure for the 50mm shots to make sure the highlights and shadows record enough information.

    Confused yet? I am.
     
  3. Rol_Lei Nut

    Rol_Lei Nut Member

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    Better example, if you photograph the cat sitting on a pile of coal in a snowy lanscape:

    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.
     
  4. timk

    timk Member

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    incident readings will be the same as it doesn't really care about the subject (only what light is hitting the subject)

    however if you take a reflected light reading with the handheld meter. The meter will have it's own 'field of view' (it probably will say in the manual for the meter). So whatever that field of view is will be what is averaged to give you the meter reading.
     
  5. Pinholemaster

    Pinholemaster Member

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    No, this was a question on a recent quiz my students took. Focal length is not a factor in determining exposure (except in micro/marco situation when one must calculate bellows extension).
     
  6. Mike Kennedy

    Mike Kennedy Member

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    Thanks all!!
     
  7. Pumal

    Pumal Member

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  8. Christopher Walrath

    Christopher Walrath Member

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    Yeah, um, no. f/4 is f/4. Just a larger entrance pupil in a longer lens than a shorter one. Ratio of diameter to length remains the same.
     
  9. Pumal

    Pumal Member

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    Last edited by a moderator: Feb 21, 2010
  10. benjiboy

    benjiboy Subscriber

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    My experience of using a separate meter with prime lenses and zoom both with daylight and flash(strobe) leads me to believe that there is a significant difference between you're 50mm f1.7 prime lens and you're 80-200 zoom , because apertures are proportions, for example f8 means that the diameter of the front element of the optic divides eight times into the focal length and is no real indication of how much light is passing through the lens,which is why in the film industry zoom lenses use T stops not f stops because they are a true indication of light transmission, so with a 80-200 zoom the light has to possibly go through twelve or more elements before reaching the film I find it's a case of getting to know you're own equipment, and giving a little more exposure with the zoom bases on you're own experience.
    I find that as other members have written that with lenses of different focal lengths because of their different angles of view if you are unable to get close to the subject a spot meter is very useful, but if you don't have one I find that taking an incidental light reading if the subject isn't too far away can do the trick.
     
    Last edited by a moderator: Feb 21, 2010
  11. Q.G.

    Q.G. Inactive

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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.
     
  12. Mike1234

    Mike1234 Inactive

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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).
     
  13. T42

    T42 Member

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    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 a moderator: Feb 22, 2010