Basic trigonometry. God, even the numbers are the easiest possible to calculate (dont even need a calculator for that baby). You need a 90 degree lens horizontally to just cover the object. The way to calculate f.l. is to use same ratios of film/sensor size to focal length as object size to object distance. Since your object distance is half the object size, your focal length needs to be half the sensor horizontal size which means a 18mm lens for FF 35mm film or a 12mm lens for APS digital. Even wider f.l. for slightly more coverage than the object itself. jco
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Shel Belinkoff Sent: Friday, December 22, 2006 3:53 PM To: PDML Subject: Determining a Focal Length There is a photo I'd like to make, but the widest lens I have is still too long as it forces me to include an undesirable object in the frame and I don't want to mess around with cloning the object out of the scene. I will need to borrow a wider lens, but I don't know what focal length would work. Is there a way to determine the focal length I need based on the subject distance and framing I want using the longer lens. I know how close I must get to the subject to eliminate the unwanted element. Perhaps a formula of some sort? For what it's worth, the subject is about 12-feet long and I have to get about six feet from it. Shel -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
