In article
>My N90s seems to be underexposing in center-weighted and spot metering
>modes. It seems to be worst when a scene is half bright and half dark
>like a lake scene in which the horizon is in the center of the screen. A
>+2/3 stop compensation usually fixes it, but I would (obviously) rather it
>would be correct, especially since I use manual focus lenses often.
>
>Anyone else had this problem?? Is this inherent in this camera or do I
>need to send it in to Nikon for service?? I don't know how long this has
>been a problem as I just recently started shooting chromes over print film
>and that's when the trouble first appeared.
Being unaware of your exposure sophistication level, I may offend you by
saying the obvious to you in the following - sorry! Meters can only average
what is within their angle of acceptance - and if the ASA setting (for the
particular film emulsion batch and processing) and the meter calibration
(assuming that the shutter speeds and apertures are without errors) are
correct, the result of any metering of any subject will be a medium grey
(often called 18% grey) tone on the film when the tones within the metered
area are mixed. The obvious examples: snow, metered "correctly", but not compensated, will be middle-tone on the film; coal in a basement, metered
"correctly", without compensation, will be midle-tone on the film - the
meter cannot tell what the subject tone "should have been", only how to
make any subject tone the middle tone on the film. With your example, the
water may be one stop below middle tone, and the sky two stops above middle
tone. When averaged by the meter, the result will be underexposure if the
metering was evenly split between the two tones. I would avoid spot-metering,
since doing it accurately requires considerable exposure knowledge and experience. (Uh, just WHERE in the scene IS that small area of middle tone that can be sucessfully metered, huh? Good spot-metering requires a set of exposure readings to be made, with some judgement necessary in making, and making use of, the readings - otherwise the spot-meter is the quickest way
to exposure error.) I find it useful to use center-weighted metering, including a range of tones in the metered area roughly equal to their proportions in the photo, with some shifting to compensate for (and minimize the effect of) unusually bright parts (a finger covering little but the sun
is a sometimes useful extreme example of this). (Snow, I find, is best read directly, with + 1 2/3 or so exposure compensation added to bring it to near white.) Color negative materials will cover a multitude of exposure sins,
with B & W negatives covering far fewer, and slide materials covering virtually none at all (+/- 1/4 stop is sorta exceptable, if you are not
being really critical, or if you are not trying to match densities within a set of slides. I find that auto exposure, even Matrix exposure, is not sufficiently accurate for slide work - with a little experience, you will
soon equal, then better the exposure success rate using manual exposure
- just remember that the meter turns everything to middle grey, and that
that may not be correct. For experience, it is useful to meter an 18% grey card to get an idea of the incident light level hitting a subject, then
meter common subjects like grass, skin tone, different sky types, snow, etc. in the same light to see how they are different from middle tone (the hand aimed back at the camera, and grass, make good metering substitutes for difficult situations, but must be compensated to give correct exposures).
If you get reasonably good slide exposures (with some too dark, and more
too light - with most about right) with Matrix metering, it is unlikely
that the problem is with the camera, and more likely it is with the
exposure technique (keeping in mind that it is common for + or - 1/3rd
stop compensation to be needed at all times with particular camera bodies
to bring their meters to "normal" exposure [use slide film {other than
Velvia! ;-} for judging this, since there is so little "latitude" with it]).
Hope This Helps