On Fri, 14 Mar 2003 14:58:37 -0500, tmorley@bmtc.mindspring.com (Tom Morley) wrote:

>In article <O4qca.11$kR2.5@tornadotest1.news.pas.earthlink.net>, "el sid"

><217linden@earthlink.net> wrote:

>> "EDGY01" <edgy01@aol.com> wrote in message

>> news:20030314120622.24725.00000060@mb-md.aol.com...

>> > << I've posted a couple of tips on how to deal with vignetting when using

>> > ultrawide lenses [12mm Voightlander]

[...]

>> > I haven't run into that problem with my ultra-wide lens (13mm Nikkor). Is

>> > it a

>> > design problem with the 12mm Heliar that you are adjusting for? Maybe a

>> > better

>> > lens will avoid this in the first place.

The Voightlander 12mm is an excellent lens in terms of

sharpness, but, as pointed out below, design-type

differences can make a difference in illumination

characteristics...

>> i think maybe the design for reflex cameras causes less of a problem like

>> this , than do extreme wide angle lenses designed for a rangefinder camera.

>A wide angle lens will have a certain ammount of light fall off

>due to the fact that the ammount of solid angle of view per

>square mm of film decreases as you go to the corner. In

>other words a given solid angle of view covers a smaller ammount

>of film if it is in the middle of the frame.

This is true for lenses with nearly symmetrical designs

(though design steps can be taken to make the aperture

size appear larger off center than it would normally

appear, passing more edge light). For very asymmetrical

lenses with larger than normal back-focus distance, the

illumination can be quite even even with super-wide

rectangular-perspective lenses (like the Nikkor 13mm).

Lenses for rangefinder cameras tend to be of the first

type (easier to design, more compact, cheaper to make -

though some recent Leitz lenses are hybrid designs, to

clear the meter and to even-out illumination); lenses

for SLRs tend to be of the second type, to provide

space for the mirror to clear the rear of the lens.

>Fish eye lenses (can) avoid this.

Yes - and they can be optically superb, with

relatively few elements (Nikkor 16mm f3.5...).