BetterPhoto Q&A
Category: New Answers

Capturing Motion - Where and When to Focus

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January 09, 2009

as none of the more experienced photographers have responded yet, I'll give you my amateur advice.

First of all, you didn't make it quite clear what you were trying to achieve. I'm guess you want your subject frozen, with a blurred background? You also didn't say what settings you were using on your camera. If this is the effect you're looking to achieve, then you'll need to make sure your camera is set to continuous focus. This will attempt to keep focusing on your subject as you pan. Yes, I'd say panning was the easiest way, as you can track your subject for a while, giving the camera a better chance of finding the correct focus. With continuous focus you won't hear that beep you get when the focus locks. Just hold the shutter release half pressed and pan. You'll probably be able to hear the lens adjusting focus.

The easiest way to do this is to set the camera to sports mode- looks like a running man on the dial. But, this takes away your control of aperture and shutter speed. Look in the manual and it'll tell you how to set continuous focus. Shoot in manual mode, then you can try f2 if you want. I might suggest a smaller aperture though to start with. F8 or so might give you a little leeway in focusing as your subject whizzes by.

Nick.

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January 09, 2009

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January 09, 2009

you want a shallow DoF, but with spot-on focus, on a kid running towards you, right? Then set AF-C:

From the D70's manual, page 64:

• AF-C (continuous-servo autofocus): Camera focuses continuously while shutter-release button is pressed halfway. If subject moves, focus will be adjusted to compensate (predictive focus tracking; 65). Photographs can be taken whether or not camera is in focus (release priority).

From the D70's manual, page 65:

If the camera autofocus system detects that the subject is moving when the shutterrelease button is pressed halfway, it will automatically initiate predictive focus tracking.
If the subject is mov ing toward or away from the cam era, the camera will track focus while attempt ing to predict where the subject will be when the shutter is released. In single-servo autofocus, the camera will initiate predictive focus tracking if the subject was moving when the shutter-release button was pressed halfway. Focus will lock when the subject stops moving. In continuous-servo AF, the camera will also initiate predictive focus tracking if the subject starts moving after the shutter-release button is pressed halfway. Focus will not lock when the subject stops moving.

Predictive focus tracking is not available in manual focus mode.

Have fun!

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January 09, 2009

For years, photographers learned how to "trap" subjects in order to capture focus at a particular instant.

"Trapping" is a simple technique where you anticipate where the will be and pre-focus there.

Two schools of thought here:

1)High ISO, small aperture=Greater DOF
This technique helps insure your area of focus is deep enough to capture the subject.

Drawback: Too much is in focus, including background and slower shutter that may introduce image blur.

2) Lower ISO (less noise), wide aperture, fast shuter

Drawback: Focus is critical as DOF is shallow.

While today's continuous focus DSLR's are much better than even a year or so ago, they are not infallible.

EX: If the subject moves out of the frame even briefly, the camera will now "hunt" in the attempt to re-aquire focus..(i.e)..You probably missed the shot.

Good "trapping" skills requires some practice and a understanding of the difference between predictable and unpredictable subject position.

Ex 2) If I wanted to capture a great shot of a pole vaulter at the apex and have the crowd out of focus, I would prefocus on the bar itself (f/2.8 perhaps) before the attempt is made. Camera is now in manual focus. Don't touch anything and don't move..wait for the action and shoot.

When it counts; I will always resort to "trapping" my subject.

Pete

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January 09, 2009

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January 11, 2009