At 07:16 12/29/01, Wayne Harridge wrote:
John wrote:
> I vote for "cos^4 fall-off;" all lenses have some of this fall-off in the
> corners. The shorter the lens the more pronounced the effect; the wider
> the aperture the more pronounced the effect; and the some lens
> designs show it more than others.
[snip]
Strange that this effect is not more noticable in "normal" daylight shots,
especially with a lens like the 50mm f1.4.
[snip]
> For a classic of fall-off with horizon lighting that exaggerates the
> effect, see this one made with the 18/3.5 Zuiko:
> http://johnlind.tripod.com/oly/gallery/om57.html
> In this case lens and aperture were deliberately selected for the
> effect it would have.
With that lens I'd expect that amount of visable fall off.
Why I posted the link to it :-)
OTOH I have other 18/3.5 photographs without visible fall-off, and some in
which it's subtle. I believe it's there and it's a matter of aperture
combined with subject material that tends to conceal it or makes it easier
to detect. Most lens designs at about 40mm and longer (35mm small format)
greatly decrease its magnitude. I would expect much greater difficulty
detecting it in a photograph made with a 50mm, even wide open, and almost
impossible to find with long lenses. The ray paths are much closer to
pariaxial.
[Someone else mentioned shooting a "northern sky" which applies here; would
be "southern sky" where you are.]
-- John
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