The rumored Nikon D3100 was announced last month, but has not yet been released. Slowly however, sample images, and videos, and hands on reviews are starting to trickle in. Here’s the first video I’ve seen recorded by the D3100, demonstrating use of the continuous autofocus.
I think the quiet ticking noise you’re hearing is the camera focusing the lens. The author comments that he has the camera in spot focus mode, so presumably its trying to focus on whatever is in the center of the frame, and you can see it have some trouble once in a while trying to find focus, or shifting focus from one subject to another. The autofocus looks similar to camcorders to me. Continuous autofocus is probably what you want if you just shooting casual video and don’t want to worry about focus. The video is shot using the new Nikon 55-300mm f/4.5 – f/5.6 lens. The video has a nice fairly shallow depth of field, which is probably created by shooting at a long focal length such as 200mm.
Nikon is now the first DSLR manufacturer to support continuous autofocus while shooting video, and I expect we’ll see others follow shortly. However, Panasonic’s mirrorless micro four-thirds cameras (such as the Lumix GF1) already support continuous autofocus while filming, as do the newly announced Sony translucent mirror cameras, the SLT-A33 and SLT-A55. In fact, you can explore all the interchangeable lens cameras that support continuous autofocus while filming at Snapsort. Sony’s SLT cameras are rather unique though. Unlike the rest of the competition that use slow contrast detection for focusing while recording movies the Sony SLT-A33 and A55 use phase detection focusing even while recording movies, which is the fast high quality focusing normally used by DSLRs and mirrorless cameras. The reason most camera’s don’t or can’t use phase detection during movies is that they have lifted their mirror up to let light into the sensor, which means the phase detection focusing system doesn’t receive any light. Sony gets around this with their translucent mirror, which lets both the sensor and the focusing system receive light at the same time. This means the Sony SLT cameras have the potential to have the best focusing systems for recording movies of any interchangeable lens camera.