I do all of my DOF in photoshop these days. For it to look good in bryce you have to be on at least 144 PPI and that's just aweful for rendertimes, and also you don't have that much control in bryce. I render a distance mask pass (delete anything that's far away or really big beforehand, or else it will render flat gray.) Then in photoshop I overlay a gradient in the front and back if I want to exaggerate the effect. Make a new channel, and paste the depth mask into it. Then go back to the main pic, and select filters>blur>focus blur. Set the channel you created as the source, and then click where you want the focal point to be, and mess with the settings until you are happy. You can control everything from the amount of blur to the shape of the circles to the rotation of the virtual blades and also let's you blow out highlights in out of focus areas, very useful tool and you have total control. Also if you don't change the point of view you can just apply it to any further renderings of the scene.