On 3 Apr 2005 at 14:57, Don Sanderson wrote: > Rob, in one of your posts you said: > > "Har told ya, also I suspect any visual focus error on > the DA is likely due to a spherical field of focus." > > What exactly does that mean? > Can a viewfinder and focus confirmation signal actually > be wrong for one lens and OK for others? > A D viewfinder is too small to be really critical, but > with the 2x magnifier detail in the roof is very clear.
Some lenses exhibit focus shift due to the effect of spherical aberrations and aperture settings. If you wish to negate this possibility then you need to set focus at the taking aperture. So yes VF confirmation wide open can be wrong, also most non-macro lenses don't guarantee a flat field of focus. Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://members.ozemail.com.au/~distudio/publications/ Pentax user since 1986, PDMLer since 1998
