Announced in late August 2009, the Sony A850 was a variant of the top-of-the-line Sony A900. The cameras are essentially identical with the A850 having the software image buffer-rate programed slower than the A900. Translation, it will only shoot 3fps, whereas the A900 will shoot 5fps. (You can actually have your camera repairman load in the A900 software and then the cameras are identical).
The other advertised difference is the view finder coverage. The A900 is advertised as 100%, and the A850 is 98%. When they were released, I held both in my hands and looked through each view finder. I couldn't see one bit of difference. Neither could the salesman. We chalked it up to marketing.
In any event, the camera boasted a stellar 24.6-megapixel full frame image sensor and delivered the best images I had ever seen from a digital camera. They are phenomenal images! Not being a 'sports' photographer, we selected the A850 over the A900 as I could care less about shooting a rapid secession of images and neither was particularly fast anyway.
The A850 is one of the most over-built cameras I have ever used. It is exceptionally strong and robust. The all-metal frame construction is evident in the feel of the camera. You don't have to be especially gentle with it either. It's made to endure heavy use. The weight is substantial, you know you are handling a very serious camera when you pick it up.
Lens selection is incredible. You can use all of the very fine Minolta A series lenses, Sony's A series lenses including the Grand Master and Carl Zeiss A series as well. Of course, there are a host of lenses from third party manufacturers like, Vivitar, Tokina, Tamron, Sigma, Cosina and adaptors to let you mount Canon, Nikon and Lecia's lenses.
This is without question my favorite DSLR. Everything is logically laid out. The menus are super easy to understand and navigate. The controls all have a solid-well-made feel to them. They turn with positive actions and detents. The camera body is extremely well sealed against wet environments.
The Sony A850 is always in my camera bag and is my camera of choice when shooting Architectural, Lifestyle and Product photography. I am constantly comparing the images from the A850 with the newer cameras that come our way. I have yet to see better.
As a working professional who shoots every day, the Sony A850 has just been perfect. I have two A850 bodies. One stays in the camera bag, the other in the studio. My main A850 is nearly 13 years old and has well over 150,000 clicks without ever giving me a problem. That’s serious build quality. Exactly what you want from a professional camera.