[LargeFormat] Re: lens corner definition

[largeformat@f32.net]

   >>I think someone recently talked of using a 90mm Angulon on 5x4 and stopping
   >>down to f32 for maximum sharpness in the corners.  There is an excellent
   >>lens test table published on the Net by Christopher M. Perez/Kerry L.
   >>Thalmann- showing definition in centre, middle and corner of field for
   >>dozens of lenses.  The conclusion might be drawn that stopping a lens down
   >>to minimum aperture does not optimise definition.  I expect diffraction is
   >>the problem  F22 or F16 is fine.
   >>
   >>Philip Lambert

The issue with the 90mm Angulon is coverage.. The 90mm Angulon  really only just covers 4x5 ........  It has a large circle of illumination but the image circle of good definition is a lot smaller. If you want to guarantee good definition at the corners on 4x5  with the little 90mm Angulon then stopping down to f32 is the way to go. Yes you will have diffraction effects at f32 but overall the image will be (subjective) better in terms of resolution at the corners.

Just in case you were wondering, this is the origin of the name of the f32.net website :-)

Some people may tell you that f22 will do the job, however the degree of resolution in the corners which is acceptable is a purely subjective issue. Vignetting is also reduced at these smaller apertures.

The 90m Angulon is a superb little lens if you manage to find a good one!

All the best,

                Clive     http://www.f32.net