Canon 85-300 f4.5 - Infinity Focusgreenspun.com : LUSENET : Canon FD : One Thread
I've noticed when using this lens that it focuses to infinity (at 300mm) when the barrel markings indicate a distance of around 30m. When I turn the barrel to the infinity mark it goes out of focus again.
Is this common with this lens (or any longer focal length lens) or is there something wrong with my example?
Thanks in advance. Dean.
-- Dean Varney (email@example.com), May 14, 1999
Dean, No, this is pretty much normal - especially for telephoto lenses. Typically they are adjusted to focus "beyond" infinity at normal room temperture. When the lens is use on a hot sunny day, it will expand and will likely focus to infinity at the infinity mark.
-- Karl Wessendorf (firstname.lastname@example.org), May 14, 1999.
This is especially true of the L Series lenses. The low dispersion and spherical elements expand and contract at a different rate than the other lens elements. Thus some play to make sure you can always focus to infinity.
-- Terry Carraway (TCarraway@compuserve.com), June 01, 1999.
Thanks for those replies. I've tried leaving the lens standing in the sun for a day to check this out (!) and the infinity focus point definitely moves.
BTW, the shots taken using the lens are fine!
-- Dean Varney (email@example.com), June 03, 1999.