LuxRender HELP

i have been working on this helmet now for about 6 hours in total. i have recently gotten into working with lux render (very helpful). i wanted to make this image so that the front of the helmet would have no blur and the back would have just enough that you gould barily make out what it looked like, but still get the general shape. i am NOT using f/stop but rather just lens radius. when i used f/stop, it made the whole image blury. i am tracking the blur to an empty that is right on the inside of the helmet. my lens radius is 0.1 and you can see that the image is not quite what i described. please help if you know how i can fix this…

go to my friend, have a look at the virus tutorial… hope it works with luxRender, if not… please excuse my ignorance:

i see what he is doing, i am using luxrender 0.7 with blender 2.49b, i dont have that option, besides, he is using blenders renderer, i am trying to practice using lux render, but thank you for the help