First, a little tech lesson: most DSLRs have imaging sensors smaller than a standard frame of 35mm film. On Nikon and Canon’s prosumer DSLRs, it is approximately the size of a piece of APS-C film. Nikon refers to these sensors as “DX”, and their recently introduced 35mm sized sensors as “FX”. Since the imaging area on the sensors is smaller, less of the light coming through the lens hits the sensor. This means that a 50mm lens on a 35mm film camera (or an FX DSLR) will act as a 75mm lens on a DX body.

DX bodies were the only game in town for a few years, so Nikon started producing lenses with the DX label – signifying that they were only suitable for DX bodies, as the circle of light coming through the lens was too small to fill an FX sensor. This reduced production costs, and has spawned a number of cheaper lenses.

Of course, now that Nikon is making FX bodies, a lot of photographers have realized they have a mix of regular lenses and DX lenses – and the DX lenses will be less than useful on an FX body.

Luckily, the only DX lens I own is the Sigma 10-20mm wide angle. It’s a great lens for what it does, but on my D200 – which is a DX body, it acts as a 15-30mm lens would act a FX body. Further, I already own an AF-S 24-120mm lens, which on an FX body reaches nicely into the field of view of the Sigma gives on the D200. See where I’m going with this? If I were to sell the Sigma 10-20 and my wife’s D60 (and give her the D200), I could probably get $900 out of the pair, maybe $1000. That’s almost half the current street price ($2,200 or so) of Nikon’s entry level FX camera, the D700. The D700 has the sensor and the brains of a D3, less some of the speed, in a D200 sized body.

Liquidating some other unused assets (my sadly neglected XBox 360 comes to mind) and devoting the rest of my discretionary cash into a camera fund means that I might be able to get a D700 before it’s replacement is announced. Even if Nikon jumps the gun and releases a new D700 or it’s replacement, camera stores will be dumping their old supplies of D700 bodies on the market, possibly driving the price down even more.

So, all I have to do is save up $1200 and find a buyer for the old camera and a lens. That’s… going to be hard.