On Mon, Sep 19, 2011 at 10:50 PM, Larry Colen <[email protected]> wrote: >> > Diffusion or diffraction? > It was my understanding that diffraction happens at any opaque edge within a > range that is determined by the wavelength. Therefore the larger the > aperture the smaller the percentage of it that will be subject to the > effects of diffraction. > > f/64 on a 320 mm lens would be an aperture of 5mm, which would be the same > as f/10 on a 50mm lens or f/8 on a 40mm. > > I suppose that it's possible that the angle of incidence of the light beams > hitting the aperture could affect the amount of diffraction, and therefore > it's not a linear function that diffraction becomes a problem with apertures > of 2mm or smaller in diameter. > > It's also been roughly 30 years since I took a course in either physics, or > field equations, so I could be completely off base.
Aperture values are ratios, not absolute values. f/64 on LF is going to be a different size than f/64 on 35mm. On a 320mm lens, f/64 has an aperture diameter of 5mm. On a 50mm lens, f/64 would have an aperture diameter of .78mm. (This doesn't account for the fact that the aperture blades aren't necessarily at the nodal point in a lens, and you are talking about a simple lens, reality is a bit messier.) Your numbers are completely wonky. > > -- > Larry Colen [email protected] (from dos4est) > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and > follow the directions. > -- David Parsons Photography http://www.davidparsonsphoto.com Aloha Photographer Photoblog http://alohaphotog.blogspot.com/ -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
