I found a website with an optics-as-related-to-photography FAQ file with a technical bent.
http://www.photo.net/learn/optics/lensFAQ I made the an observation about the following question/answer What is the basic formula for the conditions under which an image is in focus? A. There are several forms... 1/Si + 1/So = 1/f (Gaussian form).... The answer has the same form as the formula for parallel resistors (electrical analogy), and I find the following calculation easier: f = (So*Si)/(So+Si) (product /sum) I'm noot sure what the answer 'f' means, however...if I use the numbers Si = 150 mm and So = 900 mm, envisioning an object 900 mm away from the lens and 150 mm between the lens and the film, which seem reasonable for a 4 x 5 camera... The result is 128.6 mm. I don't understand if this answer represents a physical distance, a focal length or what else... the distance between lens and object and lens and film were specified, so I don't know what else there is to figure out here. If it is focal length, that sounds like cart-before horse...one has limited focal lengths to choose from...whatever fixed lengths the lenses come in. I can do the math, but making it mean something is not working for me. Thanks Murray _______________________________________________ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers
