The camera's meter may be used only within the shutter speed range covered by the exposure value (EV) range of the meter, which varies with the aperture and ASA/ISO settings. The charts on pages 68 and 69 show the relationships between the f/stop, shutter speed and film speed, indicating the usable functioning shutter speed (for metering purposes) with any film speed/aperture combination. Careful attention to the following instructions will assure precise exposure, automatically over the complete exposure control and metering range capability of your Nikon F3AF.

What is EV?
Exposure Value (EV) is the number representing the available combinations of shutter speed and aperture that give the same exposure effect when the scene brightness and ASA/ISO remain the same. At ASA/ISO 100, the combination of one-second shutter speed and an aperture of f1.4 is defined as EV1. If the aperture is stopped down by one full f/stop, or the shutter speed is one step faster, the EV increases by one; if the aperture is opened by one full f/stop or the shutter speed is one stop slower, EV decreases by one. Using ASA/ISO 100 as an example, 1 sec. at f/2 represents EV 2, 1 sec at f/5.6 is EV 5, while 1/235 sec. at f5.6 represents EV 12. Because the exposure is the same, 1/30 sec. at f/11 and 1/1000 sec. at f/2 both represent EV 12.

How to read the EV chart
Section A of the chart shows the usable EV range depending on the lens' maximum aperture in full-aperture metering, while it also indicates the usable EV range for aperture settings in stop-down metering. Section D shows the value for the ASA/ISO film speed, section B the aperture settings for various film speeds and Section C the shutter speeds to match any film speed/aperture combination.

In practise, you will find that it is generally the high end and the low end of the metering range which require a careful check. The EV range of the Nikon F3AF encompasses most lighting situations, and it is only under very dim or very bright picture taking situations that you need pay and special attention.

Full-aperture metering
Use the Nikkor 50mm f/1.4 lens and a film speed of ASA/ISO 100 as an example. By referring to the f/1.4 column in Section A and the EV value indicated for the ASA/ISO 100 in Section D, you will find that the F3AF's EV range in this case is 1 to 18. If the lens is set at f/5.6, refer to Section B and single out the protruding line intersects with Section C's vertical line for a shutter speed of 8 sec. (the F3AF's slowest shutter speed). From this point of intersection, follow the horizontal line that leads to the Section D's EV value for ASA/ISO 100, and you will obtain an EV range of 2. Start again from the f/5.6 indication for ASA/ISO 100 in Section B, and go down diagonally until the protruding line intersects with Section C's vertical line for a shutter speed of 1/2000 sec. (the F3AF's fastest shutter speed) this time. Then follow the horizontal line that leads to Section D's EV value for ASA/ISO 100 and you get a reading of EV 16. This means that an f/stop of f/5.6 at ASA/ISO 100 and at shutter speeds from 8 to 1/2000 sec., the effective metering range is EV 2 to 16, which is well within the F3AF's metering range of EV 1 to EV 18.

The green area in Chart 1 encompassed by the heavy lines in Section C demonstrates the usable shutter speed range to match any film speed/ aperture combination at ASA 100. (The minimum aperture of the lens is f/16). Similarly in Chart 2, the usable range (at ASA/ISO) for the AF-Nikkor 80mm f/2.8 lens is shown in green.

Two red lines in Section C of both charts indicate the EV value ranges of the scene brightness usable with autofocus or focus-aid operation. Therefore, the combinations of shutter speeds are apertures indicated in the areas outside the lines are not usable.

Stop-down metering
For stop-down metering, Section A indicates the usable EV range for various aperture settings. For example, if the lens is stopped down to f/8 at ASA/ISO 100, refer to the f/8 column in Section A and the EV values indicated for ASA/ISO 100 in Section D, and you will find that the EV range for f/8 is EV 6 to 23. Now single out f/8 at ASA/ISO in Section B. Go diagonally down until the protruding line intersects with section C's vertical line for the shutter speed of 8 sec. From this point of intersection, follow the horizontal line that leads to Section D's EV reading of 3. This means that an f/stop of f/8 at ASA/ISO 100 and a shutter speed of 8 sec. give an EV value outside the metering range. To find out the slowest shutter speed usable, follow the f/8 indication for ASA/ISO 100 in Section B diagonally down until it intersects the horizontal line in Section C that leads to section D's EV value of 6 for ASA/ISO 100, and you will find that the slowest shutter speed usable is 1 sec. In other words, at f/8 at ASA/ISO 100, the available shutter speed range from 1 to 1/2000 sec. has an effective EV range from EV 6 to 17 (indicated by the broken line in Section C) - well within the metering range.

Tips On Camera Care:
Although the F3AF is a tough and durable camera, bear in mind that it is a precision optical instrument and that careless or rough handling may damage it. Observe the following tips and the F3AF will always work as perfectly as the day you bought it.