12-25-2013 11:38 AM
I purchased a T3 as a gift. When taking pictures using the viewfinder everything seemed to worked fine. When using live view shooting it would take several seconds to auto focus and even then it would only successfully focus about 50% of the time. I was shooting indoors with relatively low light. I also noticed that during live view shooting the flash did not automatically pop up or flash to assist focus as it did while using the viewfinder. The setting was on auto and I was using live mode for focus. Is this normal or are there other settings that could help?
12-25-2013 11:54 AM
12-25-2013 01:44 PM
Tim's reply is great!
I can only add a little...
Part of your difficulty was the low light situation. All AF systems slow down in lower light, until it's too dim for them to focus at all. You can help them by shining a small flashlight onto the subject until the camera focuses. Or with an accessory flash mounted, many of those can emit a Focus Assist grid. If not wanting to use a large flash, a smaller flash controller module called an ST-E2 can be used to emit the same sort of Focus Assist grid. Those grids are not too intrusive, red light.
In good light, you will find that Live View/Contrast Detection focusing is the most accurate, although it's slow.
Using the viewfinder instead, you have several AF modes to choose among. One Shot is the most accurate of those, but is only usable with stationary subjects. AI Servo is for moving subjects, and is designed to track and constantly update as the subject moves. (AI Focus really isn't a focus mode, per se... it's supposed to detect for you whether or not the subject is moving, then change to using the correct mode).
You can help the viewfinder-based focusing system by manually selecting a single AF point, rather than leaving it up to the camera to choose. Use the center point as much as possible, since it's more sensitive and faster to acquire and/or better at tracking.
It also should be noted that the lens being used makes a difference in AF performance. There are basically three types of focus drive: micro motor, STM (stepper motor) and USM (ultrasonic motor). USM is the fastest and most accurate. STM is the quietest and can be preferable with video (but not all camera models can autofocus while shooting video). Micro motor is the least expensive, generally tends to be slower and noisier, sometimes less accurate.
A lens with a large aperture rating, such as "f2.8" or "f2" or "f1.4" also delivers more light to the sensors, so can help with AF performance.
Much more info about getting the best out of Canon AF systems can be found on YouTube in three approx. half-hour videos starting with this one: http://www.youtube.com/watch?v=iAx86nblZ2g It's a few years old now, but still very helpful.
Finally, with the new 70D model Canon has introduced a new "dual pixel" focusing system in Live View (and Video)... This is a significant improvement, much faster! I'm sure we'll see it on more Canon models in the future.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
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12-25-2013 03:09 PM
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