The following write-up summarizes a comparison experiment I ran using my D90 and D80 to follow up on discussions regarding metering performance. As I've done before (see Sunny-16 vs. Metering), I first baselined against the Sunny 16 rule to see how close either camera comes to that age-old guideline. Then, I compared results for matrix metering and spot metering against the actual scene to see which came closest to representing what my eye saw. I will first summarize the setup and test results, then propose some preliminary take-aways. As always, we should do more testing to learn how best to expose various scenes.

Setup:

Equipment: Nikon D80 & D90, with Sigma 30mm f/1.4, mounted on tripod to produce consistently framed shots.

Conditions: The scene was a brightly lit 10:30am Southern California morning, camera facing due west, sun shining from South east (i.e., side/back-lit). AF mode was AF-Single. ISO was set to 200 to match the D90's base ISO, hence Sunny 16 is 1/200sec @ f/16.

Image processing: All shots are RAW, down-sized and saved as JPG in Faststone 3.6, with no other adjustments or modifications.

Results:

Experiment	D80	D90	Notes
(1) Sunny 16 Manual @ f/16	1/200sec	1/200sec	Focus point on dark criss-cross glass of house's front door.
(2) Matrix Metering Aperture Priority @ f/16	1/80sec	1/125sec	Focus point on dark criss-cross glass of house's front door.
(3) Spot Metering Manual @ f/16	1/160sec	1/125sec	Focus point on dark criss-cross glass of house's front door. Spot metering performed on gray section of pavement, pre-judging that to be the mid-gray for this scene. Same result achieved when metering off green grass (brothers green and mid-gray agree).
(4) Matrix Metering Aperture Priority @ f/16	1/100sec	1/100sec	Shot re-composed to bring focus point on palm fronds to the left of the front door.
(5) Spot Metering Manual @ f/16	1/160sec	1/125sec	Focus point on palm fronds to the left of the front door. Spot metering performed on gray section of pavement, pre-judging that to be the mid-gray for this scene. Same result achieved when metering off green grass (brothers green and mid-gray agree).
Additional experiments...	...	...	with VR16-85mm @ 16mm
(6) Matrix Metering Aperture Priority @ f/16	1/50sec	1/50sec	Focus point on Flag.
(7) Spot Metering Manual @ f/16	1/80sec	1/60sec	Focus point on flag. Spot metering performed on green (small) palm fronds to the left of the flag. [D80 spot metering missed?]

Parting thoughts

And now, at the risk of sticking my neck out too far, some thoughts about these tests results.

• Use of the Sunny 16 rule without some adjustments remains an unreliable practice. The D80 under-exposes by about 1 stop, and the D90 under-exposes by about 2/3 stops. As others have pointed out, Sunny 16 isn't so much a rule as a guideline to get you in the ballpark. Please note that results may vary from camera to camera due to component variation. Bottom line: test your camera and judge how close it gets to Sunny 16. I know that when shooting with my D80, Sunny 16 becomes Sunny 11 (f/11, 1/200 sec @ISO200). I'll need to do more testing to convince myself that Sunny 16 becomes Sunny 13 on my D90.
• Matrix metering on the D90 does not seem to have the heavy bias toward the focus point that the D80 exhibits. Experiments (2) and (4) produced pretty consistent results for the D90, even though in test (2) the focus point is in the shade whereas in test (4) it is in open sunlight.
• Moreover, Matrix metering and spot metering where also within 1/3 stop of each other for experiments (2) through (5) for the D90, whereas the D80 varied by a full stop under the same conditions.
• Somewhat subjectively, I judged the right exposure to be 1/125sec. Spot metering on the D80 only missed this by 1/3 stop, and a review of the histogram will show very minor variation. Exposure is acceptable between 1/100sec and 1/160sec, though at 1/100sec, highlight details begin to blow out. I realize this is a judgement call, and pure examination of the histogram might suggest to some that 1/100sec is the right exposure, but as a matter of personal taste, I would disagree.