On Wed, 21 Oct 1998 18:00:27 +0000, David and Liana Mikulin wrote:

>I recently bought my first SLR (Nikon N70 + Nikon 24-120 lens) camera
>and was out taking pictures today (mid afternoon). It was a sunny day
>and my camera was loaded with Kodak Royal Gold 100. I was trying to
>follow the sunny 16 rule but the following happened:
>
>- When I switched the camera to Aperature Priority mode and set the
>f-stop to f16, the shutter speed indicated 1/60 or slower. I had to
>step up to f8 to get a shutter speed of 1/125. (lens at 24 mm)
>- In manual mode with the aperature set to f16 and the shutter set to
>1/125 the meter was indicating underexposure. (lens at 24 mm) Again,
>stepping up a couple of stops would indicate the correct setting
>- In shutter priority mode, setting a shutter speed of 1/125 would
>result in f-stops of f11 or f16. (24 mm)
>
>What's going on here? Why do shutter priority and aperature prioriy
>modes result in different values when trained on the same subject (trees
>or the sky)? Why couldn't I get f16 and 1/125 using aperature priority
>or manual?
>
>Also, I was reading in one of the photo books I bought that you should
>calibrate your camera's meter. Using the sunny 16 rule as a reference
>exposure, you adjust the ISO settings (regardless of the actual film
>ISO) until your camera correctly indicates f16 and 1/125... Has anyone
>out there calibrated their camera's meter using this technique or any
>other technique?

Several things (any, or all, may apply...) come to mind:
- the camera may readout only the nearest whole shutter speed,
though it is giving you one in between in A mode...
- using 1/125th at f16 is rating the film at 125, not 100...
- in the northern US, especially in the Fall-Winter-Spring,
the "sunny-16" rule is more like the "sunny-11/11.5" rule...
- if the day is not very clear, and the time close to noon,
a fudge is also needed...
- the sun needs to be behind you for the measurement...
- the sky (or any other strongly-colored subject) is not
a good metering target, since meters have color error...
- the rule is for incident light, or true average (green
foliage is about one stop darker than "sunny-16"...)
- the lens is variable-aperture (though, by keeping it at
the short end, you have bypassed this problem)
- zoom light transmission can be off 1/3rd stop easily,
especially wide open...
- meters vary commonly by 1/3rd stop...
- metering often varies between modes...
(I wonder why some of us believe in simple center-weighted
manual metering - and even in the stop-down method, which
side-steps diaphragm and variable-resistor errors...? ;-)