using filters

I've been shooting B+W landscapes on a pinhole camera. To bring out clouds
I've been using a yellow filter behind the pinhole - in front would mean
than every speck of dirt is in focus. My problem is that specks of dirt cast
a blur/shadow on the negs. I've tried vigilant cleaning but can't seem to
eradicate them. Any suggestions on keeping contrast in the sky without a
filter? Or alternatively how to use a filter without rendering every speck
of dirt?

thanks, Jeremy.
Received on Fri Oct 25 01:11:44 2002