[hdesbois]

What is your 3D app? If you use Lightwave and by chance have Fprime, you can have a quite accurate and reasonably fast DOF preview. Maybe there are similar plugins for other packages. Anyway, you can always quick-render your scene with your 3D package native renderer at low resolution to check the DOF, then use Maxwell when you are happy with your setup (you'll have to run some tests to check if your native renderer DOF is consistent with Maxwell's, though).
HD

[hdesbois]

i dont know that fprime exist for max?

Fprime does not exit for Max, but maybe you can find some equivalent : it's a fast previewer. It's limited since it can't show most shaders, particles, or volumetrics, etc. (it can be used as a renderer as well with good results, especially as it allow fast multi bounce radiosity).



In this example, the small fprime preview was less than a minute to render (without radiosity) and as you can see, it' good enough to evaluate DOF (some material appear dull because they have been textured only for Maxwell). Maybe we can have a slightly bigger preview image in Maxwell so that we can judge DOF as well as light.
HD