I tried for years to get decent DOF in Poser (I used to be a photographer, and have a Bachelor's degree in the subject), and hated the results, which took hours and hours to produce, with inevitably no control over the finished result, other than tweaking and re-rendering, over and over....yawn. 

Once I had cast off the shackles of believing that any post work rendered over your render, er, rendered it invalid and was a Bad Thing, I realised that Photoshop + Poser = The Answer!  Convincing DOF, which you can adjust to your heart's content is within your grasp....the only problem being that, unless you're happy doing it each time manually,  you need a z-depth render, which Poser can't do without assistance....check out "Semidue's/Shaderworks" plugins for the solution to that particular Poser deficiency.

The image above is an example of DOF (and some other FX) added in post, via a z-depth render; the DOF was fully controallable and took seconds to add.

And here's how I did it:

http://www.renderosity.com/mod/gallery/index.php?image_id=1963531

If you're open to the idea of post work in a 2D app, then DOF in Poser is within your reach, effective, and contollable...if you're not, then soldier on!

My self-build system - Vista 64 on a Kingston 240GB SSD, Asus P5Q Pro MB, Quad 6600 CPU, 8 Gb Geil Black Dragon Ram, CoolerMaster HAF932 full tower chassis, EVGA Geforce GTX 750Ti Superclocked 2 Gb, Coolermaster V8 CPU aircooler, Enermax 600W Modular PSU, 240Gb SSD, 2Tb HDD storage, 28" LCD monitor, and more red LEDs than a grown man really needs.....I built it in 2008 and can't afford a new one, yet.....!

My Software - Poser Pro 2012, Photoshop, Bryce 6 and Borderlands......"Catch a  r--i---d-----e-----!"