Well now we get to talk about t-stops.
T-stops are based on the amount of light transmitted through the lens. That
controls exposure. Before TTL metering was common lenses used for critical
purposes, usually feature motion picture use where each scene had to match the
other scenes exactly, the best lenses came with a calibration chart that gave
the exact t-stop for each f-stop. The transmission factor for a given lens
depends upon the type of glass, the number of elements, to a certain extent the
quality of the coating.
F-stop only gives an approximation of the light transmitting ability of a given
lens. But is a critical measurement for determining depth of field, and overall
sharpness.
TTL meters always measure t-stops so critical calibration charts are no longer
necessary, and you very seldom hear of t-stops today.
--graywolf
----- Original Message -----
From: Nicholas Wright <[EMAIL PROTECTED]>
To: PDML <[EMAIL PROTECTED]>
Sent: Monday, September 24, 2001 1:00 AM
Subject: lens brightness
> 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. Thanks for any help.
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