Center weighted, Semi-spot and Spot meters
The light meters in all Nikon F2 Photomic finders are 60/40 center weighted. (Their sensitivity is 60% within the 12mm reference circle, and 40% on other areas.) The size and the shape of the metering area are determined by masks in front of the light sensitive cells. There is a center metering area that is larger than the 12mm reference circle, and a half sensitivity weighted metering area at the bottom. Center weighted metering is excellent for horizontal outdoor shots, as the brightness of the sky is not measured. However, since the metering area is so large, it's difficult to determine the correct exposure for very high contrast scenes. Hence there is a need to reduce the metering area to obtain more accurate measurements.

I can modify all F2 Photomic finders to semi-spot metering at no charge during their standard services, but there is a small charge for the spot metering modification as the precision masks are hand made to order. Serviced Photomic finders can also be modified, at half their standard service fees because they have to be taken apart to fit the new masks, and their meters have to be recalibrated. The modifications are reversible, but there is a charge at half the finders standard service fees because they have to be taken apart to remove the new masks, and their meters have to be recalibrated.

For spot metering, the light sensitive area is within the K screen micro-prisms circle. However, spot meter readings can change widely in high contrast scenes, and rapid changes in meter readings can be disturbing to some photographers. Therefore, semi-spot metering is better for them.

For semi-spot metering, the light sensitive area is within the Nikon screen 12mm reference circle. Semi-spot metering is more accurate than center weighted metering, but less accurate than spot metering.

K screen's 12 mm circle and micro-prisms area
viewed from behind the Nikon mask
Scaled diagram of the F2's
Center weighted metering
Spot metering modification Semi-spot metering modification