Contrast Detect AF
Aside from the viewfinder, our biggest worry about the viability of the G1 - and all non-reflex interchangeable lens cameras - is the reliance on sensor-based contrast detect autofocus. Our experiences so far - with the live view modes on current DSLRs - haven't been promising; all are painfully slow and most are close to unusable for any non-static subject.
When we visited Panasonic in Osaka last year to talk about the development of Micro Four Thirds and the G1 we were assured that our concerns would be unfounded; this is a system designed from first principles on the basis of live view only operation, and a lot of work has gone into the design of new contrast detect focus algorithms. This, we were told, along with the extra processing power of the new Venus HD engine, would mean contrast detect AF that was at least as fast as current entry-level digital SLRs using the traditional phase detect AF.
The good news is that Panasonic's engineers have kept true to their word; the focus is not only astonishingly fast for a contrast detect system; it's easily as fast as any conventional SLR in this class. And unlike even most mid-range SLRs you get 23 area auto AF and the ability to place a single AF point almost anywhere in the frame - and that's before you throw in Panasonic's remarkable subject tracking AF and Face Detection. Panasonic seems to have overcome the main problem currently associated with using live view on an SLR; focus speed.
The G1 offers four focus modes; Face Detection, AF Tracking, 23-area-focusing and 1-area focusing.
|In Face Detection mode the camera will identify and lock onto a human face.||In single area AF mode you can set both the position (using the SET button then the arrow keys) and the size (using the dial) of the chosen area.|
|In 23-area AF the camera automatically selects the right area(s) of the scene from 23 points.||Panasonic's unique AF Tracking mode starts with a central focus area.|
|Half press and the focus point will 'lock on' to the subject.||Even if the subject - or the camera - moves, the focus point will continue to track it. It works well and is very fast.|
Manual focus is performed using the focus ring on the lens. If you've activated the MF assist function the image will be magnified to 5x or 10x as soon as you turn the focus ring. It's surprisingly usable; perhaps the first time we've been able to say that about a camera without an optical viewfinder.
One very useful - and slightly surprising - feature is depth-of-field (DOF) preview, when the DOF preview button is pressed the camera stops the lens down to the selected aperture which provides you with an accurate representation of the depth-of-field of the final image. This system has advantages over the optical viewfinder in that it doesn't darken and can correctly represent the effects of large maximum apertures.
One totally unique (as far as we know) feature is shutter speed effect preview. This changes the refresh rate of the live view to mimic the shutter speed selected, producing a fairly accurate representation of how blurred subject movement will be in the final shot. This is exactly the kind of feature that shows how a truly 'ground up' digital camera system can offer significant advantages over the current crop of 'one foot in the past' digital SLRs.
|Normal Live View||DOF preview button held at F22|
|Press Display to preview the effect of the current shutter speed (here the spinning players appear as a total blur). This isn't a still; it's a live view with blurring (you really have to see it to appreciate it; we'll get a video when we can).|
Live view AF video clip
Below you will find a (very) short video clip showing the G1's autofocus in action. The clip starts a fraction of a second before the half-press activation of the focus system (with the focus preset to infinity) and ends after the 3 second record review has ended and the live view has returned. As you can see, the focus moves very quickly from infinity to its closest focus point.
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