Tuesday, January 25, 2011
Keeping Your Images On Track
AF And AI Servo Settings • Noise Abatement • Selling My Pictures
AF And AI Servo Settings
Q I’m primarily a nature/bird photographer, and I recently bought a Canon EOS 7D. I’m curious about whether using the AI Servo mode when you’re not tracking a moving subject would have a tendency to work against you. Basically, is the camera trying to track when it doesn’t need to, reacting to vibration or some slight movement? Is it best to take the camera out of AI Servo mode when you’re shooting a stationary subject like a landscape or a portrait?
Via the Internet
A AI Servo is a predictive focus feature found on Canon DSLRs; Nikon offers a similar capability called Continuous Focus. These modes are especially useful for wildlife/bird and sports photographers because they allow the photographer to “lock” onto a moving subject and keep it constantly in focus by predicting its next location. The photographer can concentrate on keeping the subject in the frame while the camera keeps the subject in focus. As I’ve written before, predictive autofocus, introduced in the mid-’80s, was one of the great game-changer advances in photography.
When I’m photographing wildlife in the field (or on my grandkids’ soccer field), I want to be able to shoot both moving and still subjects without changing my camera settings. This is accomplished not so much with autofocus modes, but rather by the camera’s custom functions. Straight out of the box, I program all of my Canon DSLRs to deactivate autofocus from the front shutter button and activate the autofocus (AF) button on the rear of the camera. From that point on, I’m using my thumb on the rear AF button to focus the camera and my index finger on the shutter button to capture, and because autofocus isn’t active on the shutter button, the focusing decision I make isn’t overridden by the camera as the image is captured.
With this setup, the AI Servo tracking is active only when you depress the rear autofocus button. Keep it depressed as you follow the action, and capture your images with the front shutter button. When you lift off the rear shutter button for a stationary shot (as for a single player on the field or a portrait), focus is locked at that location. You can reframe the image, then capture with the shutter release. When your thumb is off the rear AF button, you can manually focus with the lens’ focusing ring and override any previously set autofocus. AI Servo mode is only activated when you depress the rear autofocus button, so leave it on all the time. With this setup, you have it all.
Q Occasionally, I forget to turn on the Long Exposure Noise Reduction function on my DSLR when needed, and the camera then reminds me to do it. Is there any good reason not to just leave it activated all the time?
Via the Internet
A Long Exposure Noise Reduction (LENR) is an in-camera processing feature of some DSLRs that reduces or eliminates hot pixels that may show up on long exposures as spots that may be mistaken for noise. To accomplish this, following the initial capture, the camera takes a second exposure of the same length with the shutter closed (a black image). The in-camera software then compares the two captures, identifies hot pixels in the second image, and removes them from the first. While the camera is going through its second exposure and comparative cycle, you can’t take any new images. That’s a good reason to turn it off if you aren’t using it, but if you do leave it on, it doesn’t actually activate until you set a long exposure, usually in the one- to 10-second range, depending on the camera and manufacturer. If you’re photographing landscapes and/or working slowly, frame by frame, you won’t notice it. The feature does impact your buffer at all exposures, however, so if you’re shooting fast action, you need to turn LENR off.
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