I have been an airbrush illustrator since the early 80's. I
worked mostly with guaches, but recently revisited model
making and used my HP-C with enamels and found it
good for a variety of applications. You can get as tight as
sewing thread width or use it for large areas. Get a crown
nozzle and a couple extra nibs and needles. I like the large
gravity feed cup has a cap so you're not sloshing paint all
over your work.
Here's a look at the one I'm talking about.
http://www.arttalk.com/iwata/hp-c.htm
Good luck!