Hmmm.  I've been fighting this fight, too.  One problem is that if your diff 
material isn't absolutely creamy smooth, you have to space it quite a ways 
behind the neg to ensure that any graininess is entirely out of foucus.  I 
can't seem to find milk-white, smooth diff material available by itself.  
I've called lighting shops, tried internet searches, toured home-depot.  The 
big stores have flourescent fixtures with large white smooth panels, but you 
have to buy the fixture at say $50-$100.  I suppose I could contact the 
maufacturer of one of these.....  I once tried some plastic from a 
not-quite-clear plastic kitchen cutting board (as opposed to the white ones.) 
 Sanded it smooth.  Melted it in the enlarger.
Orbital sanding plexiglass works okay, but if you sand out to 1000 grit, for 
instance, the glass is essentially clear again.  Stick to 200-400 and space 
it behind the neg, and this works pretty well.  
One success i've had on a small scale is actually a piece of white shopping 
bag plastic.  The really thin, crinkly stuff, stretched tight.  I think the 
bag came from Ames.  You need a couple layers, spaced to cancel any 
non-uniformity.  
Ground glass is probably the only thing that will stand up to the kind of 
heat your head must generate. Two layers spaced an inch apart would probably 
give you all the difuusion and mixing you could want.  but they'd have to be 
an inch or two behind the neg, which means the surface has to be larger than 
8x10.  Is this thing horizontal or vertical?

By the way, all, the 4x5 SLR is almost done.  Does anybody have any 
suggestions for posting pictures?

Roger Stevens
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