When Sony announced the full-frame Alpha 7 and 7R, it touted them as the first full-frame mirrorless cameras on the market. That's not entirely true, as the Leica M (Typ 240) fits the bill as well. Sony has amended its PR claims to position them as the first full-frame mirrorless with autofocus, which is accurate.

But the Leica M sells for close to $7,000, and has been on backorder since its announcement more than a year ago. It's a premium camera with a full-frame 24-megapixel image sensor, no optical low-pass filter, support for Live View and an add-on EVF, and an optical finder with a mechanically coupled rangefinder. It can mount Leica M rangefinder lenses, but also supports pretty much any 35mm SLR lens (or medium format lens, if you want to get crazy) via a mechanical adapter.

The new Sony full-frame mirrorless cameras have an even shorter distance between the lens mount and image sensor than the Leica M, so they can mount rangefinder lenses as well as SLR lenses via adapters. This is old news to many NEX owners, who had previously used M-mount lenses on APS-C cameras. But the Alpha 7 and 7R are full-frame, so there's no crop factor; the 50mm Summilux-M f/1.4 ASPH. captures the same field of view on these digital cameras as it does on film.

In the past, Leica shooters who wanted a full-frame digital platform for M-mount lenses have been left with one choice: Leica cameras. If you love an optical finder, that's still your option, but if you're a happy to use an EVF, you can save a few thousand dollars by opting for one of the Sony cameras.

I've got a lot of experience shooting with Leica cameras and lenses. I started with the M8 and a 35mm Summilux ASPH., supplemented that with a Panasonic G2 and later a Sony Alpha NEX-5NSEE IT, before moving to the full-frame Leica M. I've got some personal interest in the new Sony cameras: If I discovered that I'd be happy with one of them as my primary digital camera, I could certainly reduce the amount of money I have tied up in photo equipment.

I spent the better part of last week shooting with the Alpha 7 and 7R and was able to give them a workout with a number of Leica lenses, plus a Pentax lens that has a special place in my heart. There are some key differences in using either Alpha with M-mount lenses when compared with an rangefinder camera. The most obvious is the viewfinder. With a Leica M camera you look through a bright optical finder with a fixed field of view. Bright frame lines show you the approximate field of view of the attached lens, and you focus by lining up a double image in the center of the viewfinder. Because you're looking through a fixed optical finder, there's no way to gauge how shallow your depth of field will be for a particular shot; you'll have to rely on experience and the depth of field scale that's printed on the lens barrel.

With the Alpha you've got an EVF. It's an OLED design with a 2,500k-dot resolution. It's pretty much the same as the EVF built into the Sony Alpha NEX-7See it at Amazon UK, but Sony states that optics have been improved to improve the user experience. I wasn't able to perform a side-by-side comparison, but the EVF looked great to my eye. Because you're looking through the lens, framing is precise and you get a real-time preview of the depth of field as your adjust the aperture ring.

Continue Reading: Peaking and Magnification>