After numerous leaks (isn't that always the way?) Sony have today announced the A55 and A33 DSLRs. What's interesting about these models is that they use a pellicle mirror; a semi-transparent mirror that reflects 30% of the light up to the AF sensors, and lets the other 70% through to the sensor.

This allows the mirror to remain in place whilst shooting - and as the mirror doesn't have to move, these otherwise-basic DSLRs manage a blistering 10fps. That's faster than Nikon's D3 in FX mode. Additionally, as the AF sensors are always receiving light even when the sensor is recording an image, it means that the cameras can provide fast phase-detect autofocus even in movie mode (and they record AVCHD at 1080p).

The disadvantage of using this technology is that the cameras don't have a standard optical viewfinder, instead replacing it with a high-resolution electronic viewfinder, or EVF.

Other key features include D5000-style articulated LCDs, sensor-shift stabilization with every lens, and even built-in GPS for geotagging on the A55 model.

Now, this pellicle mirror stuff isn't new technology. Both Canon and Nikon have produced (albeit in somewhat limited quantities) film SLRs with pellicle mirrors. Is now the right time to bring this technology back to market for the digital age? What would you prefer, full-time AF in movie mode or a traditional optical viewfinder?

Plus... GPS. A novelty, or a serious tool for professionals and amateurs?

Kudos to Sony for pushing the envelope - but isn't it about time that Nikon did the same, rather than continuing to produce "me too" models? Let us know your thoughts in the comments!

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