Stephen Lewis , Mar 09, 2008; 12:52 p.m.
NO. You have 2 f stops of difference, so your times should be increased by a factor of 4. But further you have things backwards. F4 means more light than F8 (by a factor of 4). If you wanted equivalent prints you would print f4 for 10 seconds and f8 for 40 seconds. Contrast relates to a variety of items...not really to the degree of enlargement. It is related to the range of density range of your negative, the type of paper you are using, and the developer you are using. I suggest you read Ansel Adams' The Negative and The Print. You are missing some of the very basic information, and these books will help you get a better overall grasp of the issues involved. The reciprocity rule has limited application for most people in both in exposing a negative and printing.