O.k. Here is a longer and hopefully less typo-Version:
A person who is involved in lens design once asked me this (trick) question:
Is the influence of cromatic abbertion influenced by stopping down ? - Sure I
sad no,
because the difference in focal lenght between the colors stay the same.
But the impact on picture sharpness depends on the aperture. It is like D.O.F!
The focus difference stays the same, but the circle of confusion is
getting smaller at smaller apertures.
Frieder Faig
On Tue, Sep 05, 2000 at 03:53:40PM +0200,
frieder.faig@xxxxxxxxxxxxxxxxxxxxxxxxx wrote:
> On Sun, Sep 03, 2000 at 02:57:19AM +0800, C.H.Ling wrote:
> > Hi Richard,
> >
> >
> > 2. I have not formally test the 180/2.8 at different apertures, since I
> > found the problem with my shot at F5.6 so I expected it was not due to wide
> > open. And then I made the assumption that "Stop down the lens does not seems
> > to improve the situation."
> >
> > C.H.Ling
> >
> Cromatic abberation is infuenced by stopping down. I also guessed wrong, when
> ased by a lens desiger. But due to cromatic-abberation the colors are focsed
> at different distances. This difference stays the same but the circle of
> confusion
> caused from this difference is reduced when stepping down.
> This is the reason why APO is more importend for fast telephoto lenses.
>
> Frieder Faig
>
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