On 15/12/06, J. C. O'Connell <[EMAIL PROTECTED]> wrote: > The diffraction limits of optical lenses are > independent of focal length and absolute aperture. > Diffraction limits are inversely proportional to > f-ratio (f-stop) and the approx formula is 1500/f-ratio > in line pairs /mm. This means at f6.3 lens would have > to first resolve ~240 lp/mm to be considered diffraction > limited and that would be quite an impressive lens > indeed. Most lenses dont reach true diffraction limited > resolution performance until f11 or smaller. e.g. > they are WORSE than the diffraction limit as f11 or wider. > I dont think you are going to find any 14mm lenses > for 35mm FF or even APS that are truly reaching diffraction > limited performance across entire format ( as good as phyics will allow > ) at > an f-stop as wide as F6.3. Aint going to happen on such a wide > angle lens, even on APS where its not as wide as 35mm.
Sometimes you make a great deal of sense John. This be one of those times. ;-) -- 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
