2) You can also reduce contrast by altering the developer and development time. Solarol developer gives low contrast, but reduces the effective speed of the paper.
Originally Posted by yeknom02
3) not at all precise. The recommendations of optimum focal length for a specific pinhole diameter vary over a wide range. I prefer Pinhole Designer http://www.pinhole.cz/en/pinholedesigner/ with a constant of 1.5. Mr. Pinhole is another popular calculator.
A site with much information is http://home.online.no/~gjon/pinhole.htm. The definitive reference book is Eric Renner's Pinhole Photography.. The definitive reference book is Eric Renner's Pinhole Photography.