Some models allow auto focus in live view mode (without the mirror flips), but this is often a fairly slow process.

一些型号虽然在不改变内部镜片的情况下也可以做到自动对焦，但是通常也是个相对缓慢的过程。

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When shooting in Live View mode, the Hybrid CMOS AF system enables speedy and accurate autofocus for photos and video.

ENGADGET: Canon unveils EOS T5i and Rebel SL1, the world's smallest DSLR (hands-on)

It had previously used the patent to "produce preview images of acceptable quality" while in live view mode to secure a licensing deal with Samsung.

BBC: Kodak suffers image preview patent ruling setback

While Nikon pioneered HD video in a D-SLR, Nikon is now introducing another industry first to enrich the user experience: The D3100 is the first D-SLR to implement full time AF for D-Movie video shooting and while in Live View mode.

ENGADGET: Nikon D3100 gets real, adds 1080p movie mode with continuous autofocus