I'm about to make a lens shade/square filter holder out of balsa wood,
black paint and a step up ring. I'm using 1/4" thick by 4" wide sheets
of balsa. Since I mainly only use one lens, I'll just make sure that it
doesn't cut off too much light at infinity for that lens. (Always
remember to check the corners of your ground glass!) If you want an
adjustable one, make two square tubes, one slightly bigger than the
other, so that the larger one slides over the smaller. Then make marks
to indicate the appropriate lengths for your lens and use step up rings
so that all your lens fit. I have no doubt that commercial type bellows
shades are very nice, but I also don't doubt that they're expensive.
PDS
I decided to use a small cardboard box, spray paint it with dull black paint,
cut it to size and go from there. I may end up using two, one to fix with
rubber bands to the front lensboard, the other to 'telescope' over the lens as
needed. It's amazing how inventive you become after your wallet has been
emptied out on expensive lenses, etc.