Metering Modes for Nikon Digital Camera

To better understand how the different types Nikon Metering works, I have just done a set of test shots with a black box and mostly white piece of paper that covers the majority of the frame. I tested using Aperture Priority under an incandescent light source using my D200. The paper does occupy the center of the frame and the black box most of the right side of the frame so while metering/focusing, I used the center point on white and the first right focus point on black and did not move teh camera between shots. Results Matrix certainly takes the entire scene into account in trying to average out the exposure i think everyone gets that BUT it does weight the exposure to what ever is under the focus point. In my test moving the focus spot from the white page to the black box produced a variation in exposure of 1 stop (1/20sec focus on black vs 1/50sec focus on white). The focus on black shot over exposed the shot by about 1/3 stop, slightly blowing the highlights on the white paper. The focus on white was about 2/3 stop under exposed. Spot meter does not take anything outside of the spot that follows the focus point (as expected). Spot metering produced the widest variation in exposures as I also expected - I would only use spot metering if I have the camera in Manual mode ordinarily. The difference in exposure between focus on black and focus on white is a touch over 4 stops (1/10 sec on black vs 1/180 sec focus on white). the white shot was 2 shots under exposed and the black focus shot was 2 stops over exposed. that tallies with the way I use spot metering in manual mode (white needs a +2ev exposure comp and black -2ev exp comp to get a well exposed image using the variation of the Zone system as applied to metering). This indicates that the meter is trying to expose both the black and white spots as 18% grey. Center weighted metering produced exactly the same exposure regardless of where the focus point was and produced a 1/125 sec exposure for both test shots. both shots were underexposed by 1.5 stops. as the center of the shot was mostly covered by the white sheet, the results are about what I would expect in this situation given the meter is trying to expose the white as 18% grey but adding a slight adjustment for the black element in the frame. Observations Matrix certainly does do some magic to try and get the exposure close to correct, it is not perfect by any means but does weight the exposure for what is under the focus point when you 1/2 press the shutter. I think that the biggest gotcha with matrix is mostly with the people who only use the center focus point, focus and then re-frame before firing the shot, the meter can get confused as the scene that is metered is not the scene that is captured when the shutter fires. This is particularly relevant in close up photography like portraits and telephoto shots, not so much for wide angle landscape shots and scene content will not change so much after re-framing. Exposure lock Would resolve the issue but I suspect that most inexperienced Users tend to forget that feature. Spot meters everything to 18% grey and the spot moves together with the focus point, very useful in manual mode once you understand that exposure needs to be adjusted +2ev for whites and -2 ev for blacks. Center weighted metering area remains constant in the center of the frame, regardless of what focus spot is used. It does make some adjustments for the whole scene as advertised, reducing the extremes in under and over exposure as see with the spot meter test but still requires the photographer learn the meter and make + or - adjustments. Conclusion There is no such thing as the perfect meter that will second guess the photographer every time, Dynamic range limitations, creative considerations and the content of the scene will always require the photographer to have skill to make right decisions and adjustments for correctly expose the shot. The spot meter is the only one of the 3 that consistently meters to 18% grey regardless of subject matter, matrix and CW both try to add some intelligence to the metering decision based on the whole scene. The lesson here is that unless you are using spot metering and making sure that you manually adjust the exposure compensation depending on the subject, keeping the camera fixed on the center focus point and re-framing after focusing will not get the best results from the Matrix or CW meters. Make use of exposure lock and the extra focus points to reduce reframing and the metering consistency should improve when using the matrix and CW features. Both functions will still require fine tuning adjustments to get the perfect settings when the subject has wide DR or is not a mid toned object. Brad Morris http://www.flickr.com/photos/k-blad