>> Pierre Bellavance wrote:
>> My thinking was that there is more risk of vignetting on the 100-400 at
>> 100mm than at 400mm because of the wider view at 100mm.
>> Who's right?
> "Ray Amos" <[EMAIL PROTECTED]> wrote:
> Actually with the 100-400 IS lens there is no vignetting at
> any focal length when using 72mm filters via a step-down ring.
> I've even used it for macro work in the 300-400 mm range with a
> 67mm filter and could not tell any difference.
Hi Ray and Pierre,
The 100-400 IS produces about half-stop of vignetting all by itself,
with and without hood, with and without filters. :-(
I have used a 77-to-72mm 72mm accessories (CPOL and Canon 250D) on
the 100-400 IS with a 77-to-72mm step-down ring. The vignetting does
not get better or worse when using 72mm accessories.
Pierre, if you go get a 77-to-72mm step-down ring, I suggest that you
also get a Tamron 72mm front lens cap to go with it.
The correct lens parameters that determine vignetting are:
1) the distance between obstructing element (filter or front element)
and the front nodal point
2) the diameter of the obstructing element
3) the angle of view of the lens (a function of focal length and
magnification).
In practice, it is easier to just slap on the filter, look through
the viewfinder, and shoot some film :-)
Cheers
Julian Loke
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