Joe and Mary Ann McDonald's

Wildlife Photography

If you shoot evaluative or matrix metering on a Programmed mode - Aperture, Shutter Priority, or just a Auto Program, then this tip isn't for you! Sorry.

However, if you shoot using spot metering, and especially if you also use Manual Mode, then CF 4-1 is a real life-saver. What is it?

As you know, when your index finger slightly depresses the shutter button the metering system turns on. On a programmed mode, of course, the camera sets the exposure at that time. The shutter button also actives autofocus, so for auto shooters, focus and exposure are acquired and determined almost simultaneously. However, if you use spot metering, you may wish to meter an area that is not on the plane of focus as your subject. If you shift your camera so that the meter is on a different area the lens automatically focuses on that spot. That usually isn't helpful since you then after reacquire the focus on your subject after making that new meter reading.

Imagine a hawk that's perched on a limb that's barely visible because of the tangle of twigs or vines or limbs that are between you and the subject. With a long lens it can be difficult to even find your subject, especially since your camera's AF may be focusing on everything but the hawk. Finally, however, you obtain focus but you worry that the subject's tonality is such that you want to verify your exposure by metering another area. This might be a thick tree limb or a tree trunk that's further back but in the same light, or perhaps a section of blue sky, or perhaps some middle-tone leaves in the foreground.

Remember, you had difficulty even finding the bird with your long lens. Now, if you try metering a new area the lens focuses on this spot when the meter is activated, right? Right, unless you're using CF 4-1. When that function is turned on, when your index finger depresses the shutter slightly the meter is activated but AF is disengaged. So, once you have focus, that focus remains fixed even if you aim your lens at a different area to obtain a meter reading. Then, after doing so, you can swing the lens back to the hawk and, because the focus hasn't changed, it should be a quick and easy matter to find your target and take the shot.

How then is auto focus activated? On the back of all the Nikon and Canon models offering CF 4-1, there are usually one or two buttons that can be activated by your thumb. With Canon there are two - one to select the AF focusing point and one to activate, or to lock, auto focus. With Nikon there's one - the AF lock, which may also serve as an exposure lock in some modes. Auto focus is activated by your thumb depressing this back button. If you're using a continuous focusing model - Servo with Canon, the lens will continue to focus or to track a subject as long as your thumb is depressing the AF button. For One Shot mode, each time you press the button the lens focuses.

It may take a little getting used to in order to use CF 4-1 effectively, because at first you might forget that you must depress the back button. I've had folks on our workshops suddenly panic when they thought their AF wasn't working because they forgot they had activated this function. However, once you get used to it the action becomes second-nature and you'll find yourself pressing the AF button with your thumb to focus and depresses the shutter button to meter together or separately as the need arises.

And, if you use spot metering, you'll find this method really eliminates a huge amount of frustration as the lens now maintains its focus point after you've acquired focus. Since a big lens also eats up battery juice as it 'seeks' focus, or racks back and forth from near to far as it tries to focus, you'll find that CF 4-1 also extends your battery life as well.

It's a happy coincidence that both Nikon and Canon have used the same Custom Function setting for this feature. In operation the two systems work similarly as well. If you try this out, give yourself a full day of shooting to get accustomed to it, because it is a habit that you must develop. A great one.

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