Nikon N90s: How Does "3-D Multi-Sensor Balanced Fill-Flash" Work?

(From Nikon N90s brochure, © Nikon Inc., 1996)

With SB-26 or SB-27 AF Speedlight and D-type AF Nikkor lenses, the N90s uses the five-segment TTL Multi Sensor to its maximum potential---the ultimate in balanced fill-flash control. This is how it works:

1. The D-type Nikkor lens sends subject-to-camera distance information to the N90s.
2. The SB-26 or SB-27 fires a series of week flashes, just after the mirror goes up but before the shutter moves, as a Monitor Pre-flash for the TTL Multi Sensor.
3. The TTL Multi-Sensor meters the light reflected from the gray shutter curtain to each of the five segments.
4. The camera's computer analyzes and decides: i) which segment of the TTL Multi-Sensor to use for TTL flash control according to a relative reading of the reflected light amount, and ii) what amount of flash is necessary to balance with ambient light according to the exposure meter used, including 3-D Matrix, Center-Weighted and Spot.
5. The shutter opens, the main flash fires and the camera's computer controls flash output based on data from 5.

Multi-Sensor Balanced Fill-Flash:

Type 1: With SB-26 or SB-27 and a non-D-type AF or an AI-P Nikkor lens: Without distance information, computation is less refined than when using a D-type lens. However, results are much superior to single TTL flash sensor system.

Type 2: Without Monitor Pre-flash: N90s's Matrix sensor provides the information on too-bright or too-dark areas included in the scene; the TTL Multi-Sensor then controls the main flash output. This method is superior to single TTL sensor system, but not as effective as when the Monitor Pre-flash is used.