Making sense of the STM lenses and the 650d AF

Started Jun 9, 2012 | Discussions thread
Senior MemberPosts: 1,208
Re: Making sense of the STM lenses and the 650d AF
In reply to caterpillar, Jun 9, 2012

Let wait for a technical review rather speculating.

I have no idea how they design and implement, but from my engineering knowledge... Stepper motor is a digital device. It is not necessarily faster than a servo-motor.

Stepper motor needs to index at the beginning of each cycle.

Because it is a digital device, Canon can program the motor gain based on each usage mode more easy than the old analog motor. In video, they can reduce the gain so focus tracking is slow and quiet. In shooting mode, they can increase the gain to get faster response.

The AF accuracy is from the sensor which resides inside the camera. if this lens mates with same old camera, same old sensor, AF accuracy won't be any better. If anything, the granularity of the stepper only make it worse I think.

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