Allow me to introduce you to Mr. Pinhole http://www.mrpinhole.com/index.php Go to the exposure guide and enter your f-stop.
A quick reciprocity table is at http://oak.cats.ohiou.edu/~schneidw/...rrections.html
I have searched out several articles on the web of exposure and reciprocity and have made my own charts which I keep in my camera bag. With a little adjusting I can hit the exposure most every time.
If you use negative film (FP4, HP5, etc.) then you print just like any photo. Works great and is a lot of fun!