Nikon F3AF User manual Part V Autofocus Problems

The F3AF provides autofocus and focus-aid operation in the majority of cases, including such difficult situations as fast-moving sports events, subjects seen through glass, or scenes containing point light sources, such as the flame from a candle or a streetlight at night. However, if the overall subject is dark in tone (e.g. when the illumination level is less than EV 4 at ASA/ ISO 100), low in contrast, or lacks a distinct vertical line, the focus-impossible warning blinks or glows continuously to inform you that the camera's TTL image displacement detecting system will not work. In this case, you can set the lens' A-M switch (65) to M and focus on the main subject manually using the matte portion of the focusing screen. As an alternative, perform autofocus or focus-aid operation using another subject, if available, which is located at the same distance as the one you want to photograph; then, with the focus lock button depressed on autofocus or without changing the distance setting in focus-aid operation, point the camera at the original subject and take the picture.

Dark subject The red X blinks to show insufficient scene brightness. In this case, focus manually, or perform autofocus/focus-aid operation on an alternate subject at the same distance which is lighter in tone.

Low contrast subject. The red X lights up continuously. In this case, focus manually, or perform autofocus or focus-aid operation on an alternate subject at the same distance which has more contrast or is larger.

Small or finely detailed subject The red X lights up continuously. In this case, focus manually, or perform autofocus or focus-aid operation on an alternate subject at the same distance which has more contrast or is larger.

Subject with no vertical lines The red X glows continuously. In this case, turn the camera vertically and perform autofocus or focus-aid operation, or focus manually; alternatively, perform autofocus or focus-aid operation using an alternate subject at the same distance which has vertical lines.


Subject with high reflectivity, backbit subject, or scene with both far and near subjects In these cases, both red arrows or the red X light up continuously. If the red X appears, focus manually. If both red arrows are lit, use the matte portion of the screen to check focus. If your desired subject is out of focus, then focus manually. If it is in focus, take the shot.

To match the convenience of autofocus, the Nikon F3AF features aperture-priority auto exposure. All you do is set the camera at A (Auto) and fire away. Light is automatically measured through the lens at full aperture, and the correct shutter speed is electronically determined to match the aperture in use.

The F3AF also lets you select the shutter speed manually for complete creative control. Because the fast-reacting SPD metering cell is located in the camera body below the reflex mirror, you have full metering capabilities even with an interchangeable viewfinder attached.

Metering is Centre-Weighted; 80% of its sensitivity is concentrated in the 12mm Ø centrer spot of the focusing screen, while the remaining 20 % is distributed over the rest of the screen. To get the correct exposure, centrer the main subject in the finder. There are three factors involved in determining exposure: film speed, aperture, and shutter speed. All must be set correctly to get the proper exposure.

Setting the Film Speed To program the F3AF to give the correct exposure with a particular film, you must first set the camera to the correct film speed. The film speed, represented by an ASA/ISO number, is a numerical rating of the film's sensitivity to a given amount of light: the higher the number, the greater the sensitivity, and vice versa. This number is printed on the film carton and the cartridge itself. To handle all film types, the camera's ASA/ISO dial (22) has settings from ASA/ISO 12 to 6400. Two dots between each pair of ASA/ISO numbers stand for intermediate settings, such as 64, 80, etc. The table above gives the speeds for all intermediate settings.

Note: In certain situations, you can set the ASA/ISO dial to a setting which is different from the recommended film speed. For example, some photographers rate their colour slide film at a slightly higher ASA/ISO setting to produce intentional underexposure for more colour saturation. Or when shooting in very low light you can "push" high-speed black-and-white film by doubling or quadrupling the ASA/ISO, then overdeveloping it to compensate for the underexposure.

EV Setting the Aperture

The second factor in determining exposure is the shooting aperture. Aperture, or the opening formed by the diaphragm inside the lens, controls the amount of light allowed to pass through the lens and strike the film; it also controls depth of field . In low light, you are generally required to use large apertures (indicated by f-numbers which are low in numerical value, e.g. f/2.8), while in bright light, small apertures are called for (e.g., f/16).

The aperture ring (68) features click-stops at whole f/stops but is continuously variable throughout its entire range. With the exception of a few special lenses, Nikkor and Nikon Series E lenses enable full-aperture light measurement regardless of the aperture setting.These lenses have automatic diaphragms, meaning that the diaphragm stops down to the preset aperture only at the instant of exposure. To keep you fully informed, the aperture in use appears in the ADR window (1) inside the camera's viewfinder.

Shutter speed, or the length of time the shutter remains open, also determines the amount of light allowed to strike the film.

The Nikon F3AF offers automatic stemless shutter speed control over the range from 1/2000 sec. to 8 sec., plus full manual control with a choice of 18 settings, including B, T, and X. All shutter speeds, except T, are electro-magnetically controlled.

The shutter speed dial has the following settings:

A (Auto): Provides aperture-priority automatic exposure control in which you first select the shooting aperture, then the camera sets the corresponding shutter speed for correct exposure.
1/2000 - 8 sec.: 15 discrete settings give you full manual control of the shutter speed.

The numbers engraved on the dial in white are reciprocals, for example 2000 means 1/2000 sec. 60, also a reciprocal, appears in red and indicates the highest manual shutter speed for proper synchronization with electronic flash (with the exception of X). Numbers engraved in orange represent actual shutter speeds, for example an orange 8 means 8 sec.

B (Bulb): The shutter remains open as long as the shutter release button (75) is depressed.
T (Time): At this mechanical setting, the shutter stays open until the dial is rotated to another setting, making it ideal for really long time exposure. To avoid unnecessary battery drain, follow this procedure: turn the power switch (73) off and make certain the LCD is not displayed in the finder, then trip the shutter using the backup mechanical release lever (6).
X (X-sync): Provides 1/80 sec. speed, the proper synchronization speed for any electronic flash unit.

To set the shutter speed dial, rotate it until the desired setting click-stops opposite the index line (10); the dial is locked at the A and X settings to prevent accidental shifting of the setting. To move the dial off a locked setting, push the locking button (77) as you rotate the dial. Intermediate settings should not be used.

When making blank exposure with the shutter speed dial set at A or 1/125 sec. or above, an 80 will appear until you reach frame one.

Automatic Exposure Control

Automatic exposure is the most convenient way to shoot with the Nikon F3AF, because it allows you to concentrate fully on the subject without worrying about the exposure. By presetting the aperture and locking the shutter speed dial (72) at A, the camera automatically sets the proper stemless shutter speed from 1/2000 to 8 sec. as soon as the shutter release button (75) is depressed halfway. To keep you fully informed, the shutter speed is displayed via LCD in the viewfinder. Speeds between 1/2 and 1/2000 sec. are shown as a reciprocal of the actual speed, for example 125 means 1/125 sec. Speeds between 1 and 8 seconds are signified by a - symbol appearing to the upper right of the number, for example 8- means 8 sec. To make the display easy to read, intermediate speeds appear in the display as a discrete shutter speed which is closest to the actual speed. (For instance, 1/287 sec. might be the automatically selected shutter speed in use, but 250 will be displayed.) The LCD stays on for approx. 16 sec. after you remove your finger from the shutter button.
Before shooting, check the exposure display.

Note: The camera's effective metering range depends on the shutter speed and aperture in use at a particular film speed.

	Use a larger aperture or slower shutter speed.
	Use a smaller aperture or faster shutter speed.
	Within +/- (1/4) EV

Manual Exposure Control

In the manual exposure mode, you can shoot at any combination of f/stop and shutter speed from 1/2000 to 8 sec., enabling you to select your desired shutter speed. Manual exposure is also required when stop-down exposure measurement is necessary or when you want to use the B, T, or X setting. Except at the B, T, and X settings, the shutter speed you set is shown in the viewfinder immediately after the shutter release button (75) is depressed halfway. As before, the - symbol at the upper right of the number indicates shutter speeds from 1 to 8 sec. Also the letter M appears to the left of the number, indicating the manual exposure mode. Above the M, the following symbols appear: -, +, and - + which indicate underexposure, overexposure, and correct exposure, respectively. To obtain correct exposure, simply turn the shutter speed dial (72) and/or aperture ring until the - + symbol appears. The LCD stays on approx. 16 sec. after you remove your finger from the button.

Intermediate settings on the shutter speed dial cannot be used while those on the lens aperture ring (68) can be. Therefore, stop the lens aperture down or open it up to the appropriate intermediate setting when fine adjustment of the exposure is necessary.

	* When making blank exposures with the shutter speed dial set between 1/125 and 1/2000 sec., the shutter fires at 1/80 sec with M 80 displayed until the frame counter reaches one.

** At the B or T setting, an M - appears in the viewfinder.
*** At X, an M* 80 appears. However, the + does not mean overexposure, because the meter does not function at this setting as soon as a dedicated Nikon Speedlight is attached to the F3AF and turned on, the + disappears from the display, leaving just M 80.