--- Tim Munro <[EMAIL PROTECTED]> wrote:
> Hey folks, I am just about to slam some money down
> for the drop-in Circ.
> Pol. filter for my 300/2.8IS - very pricey but I
> want to reduce widscreen
> glare on bright days at the track. A thought just
> occurred to me though, I
> can live with the two stop loss when panning but is
> the reduced light likely
> to adversly affect AF performance?
Absolutely. The less light the autofocus sensors get,
the slower AF is. You lose about 1-2 stops from having
a polarizer on, so your lens will focus as if it's an
f4 or f5.6 300mm. I have observed this firsthand...
the other problem as you note, is that the shutter
speed can drop too low, which can result in blurry
pictures if you're not panning carefully.
On the track, I've noticed that using polarizers to
take pictures of race cars is not a good idea unless
the light is REALLY difficult because of this. If you
do have to use one, plan on focusing manually.
Also, one of the things you will never really read
about anywhere else is that a polarizer can result in
some really unnatural "rainbow" color casts on
windshields and windows of race cars that have
plexiglas or Lexan(tm) parts on them.
Polarized light also does absolutely bizzarre things
with some of these refractive paints like the DuPont
"Chromalusion" which isn't always unpleasant, but it
is strange.
If you are after a documentary, representational
picture of a car it's best to carefully control the
light (strentgth and direction) rather than use a
polarizer.
> something I can't live with.
> I thought about it for too long and have now
> confused myself. I would be
> grateful if someone could clarify this for me.
In most cases it's my considered opinion that a
polarizer is a bad idea for race cars on the track if
you're AF'ing.
MadMat
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