Selecting the AF Mode
Two types of autofocus are available: One-shot AF and AI Servo AF. Select the mode most appropriate for the subject and shooting situation. But please take note, to use the camera’s AF modes, any compatible (Canon or third party) EF-spec lens’ focus mode switch must be set to “AF”.
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1 While pressing the AF mode selector, turn the main dial to the left or right until the desired AF mode appears in the LCD panel. 2 Release the AF mode selector. The sections that follow will outline few areas that relates to autofocusing with the Canon EOS-1N camera: |
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300 -340 km/h down the straight is not uncommon sight in Formula One racing; it can be real stressful for autofocusing tracking system as well as the photographer to capture the intense speed and atmosphere of F-1 Racing. Canon professional users with their long tele are dominant group off the track. I would think most people would associate Canon with action sports photography. They have their reasons in determining which system suit them best at work. |
Credit: Image courtesy of Mr. James North from www.F1-jimages.co.uk. The original image can be accessed via his site. Image copyright © 2005. All rights reserved. Please respect the visual property of the contributing photographer.
One-shot AF
This mode is frequently
used with stationary subjects. Common operational theory in designing one shot AF
is, the shutter will not release if the subject is not in focus, thus, preventing
out-of-focus photography. When the shutter button is pressed halfway and the subject
is focused, the corresponding focusing point lights red in the viewfinder, and the
in-focus indicator ("
") lights up in the viewfinder. In evaluative metering
mode, the shutter speed and aperture value are determined at this time, and by keeping
the shutter button pressed halfway, the focus and exposure settings remain locked,
allowing you to recompose the picture as desired.
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Further, the shutter will not release if the in-focus indicator is blinking. It blinks because due to out of range on focusing capability or even when combines with the fact that exposure is not properly metered for a good exposure. Try refocusing the subject on an alternate subject with higher contrast at approximately the same distance, or use manual focusing |
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Operation: Press the shutter button halfway to activate autofocus.One-Shot AF mode is suited for still or slow-moving subjects. Since the shutter cannot be released unless focus is achieved, it prevents out-of focus shots. When One-Shot AF is used with evaluative -metering, the auto exposure also locks when focus is achieved. |
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Pressing the shutter button halfway activates autofocusing. When focus is achieved, the focusing point flashes in red and the in-focus indicator lights. With the shutter button pressed halfway, the focus and auto exposure (with evaluative metering) are locked. You can then change the composition of the shot without changing the focus and exposure setting. Hold down the AF mode selector and turn the Main Dial to select the One-Shot AF mode.
Focus Lock:- The focus lock function is available in One-shot AF mode only (not available for the AI-Servo mode). This function is useful when, for an example, aim to locate the subject out any focusing point selection for certain creative effect. In the One-Shot AF mode, lock the autofocus, then recompose and release the shutter. When none of the focusing points cover the spot you want to focus, you must first aim the active focusing point on a specific spot. Then lock the autofocus and compose the shot. Focus lock functions only in the One Shot AF mode and maintains the chosen focus.
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Operation:- Lock the autofocus as follows: 1. Aim the active focusing point where you want to focus, then press the shutter button halfway to execute autofocusing. 2. Focus is achieved when the focusing point flashes red and the in-focus indicator lights. Focus is maintained (focus is locked) as long as the shutter button is pressed halfway. 3. With the autofocus locked, recompose the shot and press the button all the way to release the shutter. Aim the active focusing point where you want to focus, then press the shutter button halfway. When focus is achieved, the focusing point flashes red and the green in-focus indicator lights. Hold down the shutter button halfway to lock the focus. Recompose the shot, then press the shutter button completely to release for an exposure. |
"). Pressing the AE lock button activates
autofocusing. However, it may not be guarantee it will work but evaluative metering
can be a good secondary solution to equalize minor exposure changes.Al servo AF
For autofocus tracking
of a moving subject, The lens focuses the subject continuously while the shutter
button is pressed halfway. Focus Prediction (read below for more info) is activated
automatically. The Al Servo AF mode is effective when the camera-to-subject distance
keeps changing. Focus prediction tracks an approaching or retreating subject. The
subject's position at the moment of exposure is predicted to obtain sharp focus.
Exposure is determined immediately before the shutter is released.. Once the shutter
button is pressed halfway to focus on the subject being tracked, focusing is continuous
and the shutter can be released at anytime for the first shot. The following shots
can be taken once the lens focuses again on the subject being tracked. In the Al
Servo AF mode the beeper does not sound and the in-focus indicator only blinks if
focus has not been achieved while the shutter button is pressed halfway. While pressing
the AF mode selector, turn the Main Dial to select the At Servo AF mode.
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However, unlike Single Shot AF, in AI Servo AF mode, the viewfinder's in-focus indicator does not light up and the beeper does not beep even when the subject is in focus. The in-focus indicator blinks only if the subject cannot be focused. |
Further, the Focus lock feature cannot be used in this mode, but autofocus can be temporarily suspended through Custom Function CF 4-2
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AF Servo is NOT all about sports, sometimes for important shots, a series of burst are required to capture an important event, such as this Close encounter East & West, back in 1998. |
Predictive focus control The focus lock is the secondary feature for the Single Shot AF mode, but the continuous shooting mode of AI- Servo is supplemented by the Predictive focus. It continuously measures the distance and speed of a subject that is moving at a relatively constant velocity, and then predicts the subject position so that the subject will be sharply focused at the instant of exposure. When using a manually selected focusing point, it is used for predictive focusing and lights red in the viewfinder. In automatic focusing point selection mode, cover the subject with the center focusing point for initial focusing. After that, even if the subject moves to a different focusing point, the camera’s predictive focus function will continue to track the subject as long as it is covered by one of the focusing points. The focusing point does not light up.
| Custom Function CF4: | In AI Servo AF mode with predictive focusing (used for action based like sports photography, etc.), this function lets you momentarily lock the focus using the AE lock button. | |
| Custom Function CF-11: | In AI Servo AF mode, this function lets you select the focusing point with the quick control dial to manually track the moving subject. |
This EOS-1N’s autofocus
system is very accurate and can
quickly focus most subjects
with the high-precision Multi-BASIS (Base-Stored
Image Sensor)
AF sensor equipped with five focusing points as shown inside the viewfinder as well
as the top LCD panel as symbols. However, although in most cases, AF system in modern
SLRs should be able to handle most shooting situations, but it also has some limitations
and may have difficulty focusing the subjects. When autofocus is impossible, the
green in-focus indicator ("") will blink in the viewfinder.
Difficult
Subjects for Autofocus (a) Low contrast subjects (misty scenes, light-colored
or white objects) (b) Subjects in extremely low-light situations (a dark room,
night scenes) (c) Subjects in extremely strong backlight, or with bright spectral
reflections (shiny metal, snow, ice, surface of a lake) (d) Subjects with
an object in front of them (caged zoo animals) (e) Subjects having generally
horizontal patterns (only when using the center focusing point, when using lenses
with maximum aperture smaller than f/2.8) (f) Subjects having generally vertical
patterns (only when using focusing points other than the center).
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Canon suggests some solutions for these: 1) Particularly with subjects such as (a), focus on a substitute subject at the same distance from the camera as your main subject, then recompose the picture using the focus lock function. 2) In the case of (e), there is no problem when using a lens with a maximum aperture of f/2.8 or larger (except the EF50mm f/2.5 Compact Macro or EF28-80mm f/2.8-4L) because the camera’s central cross-sensor activates to detect horizontal lines. However, when using a lens with a maximum aperture smaller than f/2.8, Canon recommends using the focusing points other than the center that have vertical sensors, focus the subject, then recompose the picture using the focus lock function. 3) In the case of (f), use the center focusing point which has a horizontal sensor, focus the subject, then recompose the picture using the focus lock function. 4) Set the lens’ focus mode switch to “M” and manually focus the subject.
| Previous | NEXT | Manual Focusing + Technical information relating to improved Canon AF system.
Focusing (Autofocus/ Manual Focusing): - Part I | 2 | 3
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