Hi,
On 2001.09.24, at 20:39, [EMAIL PROTECTED] wrote:
>> I have heard remarks that a 200/2.8 prime will transmit more
>> light than an 80-200/2.8 zoom. Is this true? I thought a
>> 200/2.8 was a 200/2.8 whether it be a prime or part of a zoom.
>
> I'm with you 2.8 is 2.8. Two different lenses, if calibrated properly,
> should deliver the same amount of light at the film plane when set to
> 2.8.
> No ifs, ands, or buts!
The aperture value simply depends on geometry as William and
Nenad wrote before. I should add that not only surface light-
loss but also vignetting reflects the amounts of light coming
through the lens.
There is T-value which depends on the amount of light through
the lens. When you set the two different lenses at the same
T-value, they deliver the same amount of light at the film
plane.
I do not consider it too much to say that two different lenses
with different constructions deliver the different amounts of
light at the film plane when set to the same aperture value.
BTW, the differences between the amounts of light through the
lenses do not seem very big.
Hope this helps.
--
Yoshihiko Takinami
Osaka, Japan
[EMAIL PROTECTED]
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