nope, what you gave was impossible. 18mm and 15mm are not possible (the lengths you provided) because Pentax APS always needs a lens 2/3 the length of FF 35mm for same angle of view. I dont care what calculator you used, it's wrong if it told you 18mm for FF and 15mm for APS were the same angle of view, because they arent.
jco -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Digital Image Studio Sent: Friday, December 22, 2006 4:51 PM To: Pentax-Discuss Mail List Subject: Re: Determining a Focal Length On 23/12/06, J. C. O'Connell <[EMAIL PROTECTED]> wrote: > 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. Try again. A 12mm lens on APS format at 6' from the subject will provide a resultant horizontal field of view of 15' -- Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://home.swiftdsl.com.au/~distudio//publications/ Pentax user since 1986, PDMLer since 1998 -- 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
