Canon Mount Zeiss ZE Lenses. Wacky T-Stops Explained.

February 19th, 2010

Zeiss National Sales Manager Richard Schleuning does a good job of explaining why the T-Stops are all over the place on their ZE line of lenses. He also hints at a new T2 line of Zeiss still lenses in the future.

Click Here To Go To The Zeiss Website.

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photonashville
photonashville
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February 19th, 2010

Could cinema5D do a tutorial on t-stops, the history, the why, the how are t-stops different from f-stops, and even a listing of known cine lens makers. That would be great.

I researched it more recently and while I understand it to some degree, I bet many still shooters out there moving to video would like to have some concise information explained more than wikipedia.

The interview was o.k. to watch but gave little info on t-stops, despite the title.

jared
jared
Guest
February 20th, 2010
Reply to  photonashville

Thanks for the comment. To the best on my knowledge T-Stop means “Transmission of light thru the lens to the film/sensor”. I could be wrong. While “f” stop is a math equation without dollar signs.
Jared

Romain
Romain
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February 20th, 2010
Reply to  photonashville

“f/number

Definition: Setting of lens diaphragm that determines amount of light transmitted by lens. * Equal to focal length of lens divided by diameter of entrance pupil. * f/numbers are, for convenience and by convention, placed on a scale in which each standard f/number step (f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45, f/64 and so on) represents a doubling in the amount of light transmitted e.g. f/4 transmits twice as much light as f/5.6; conversely, f/16 transmits a quarter of f/8. * Since f/number is usually calculated from simple physical dimensions, different lens designs, varying focus and the use of accessories may all affect the actual amount of light projected: one lens set to e.g. f/8 may not give quite the same exposure as another lens set to f/8.

T-number

Definition: f/number of a lens corrected for the light loss during transmission through the lens. * f/number of a perfectly transmitting lens which would give the same illuminance on the axis as that produced by the test lens. * Equals the f/number divided by the square root of transmittance (assuming a circular aperture) e.g. if transmittance is 50% (only half light entering system exits the system), square root of a half is 1/C2, so T-number is one stop more than the f/number, so a relative aperture of f/4 with transmittance 50% is a T/5.6 lens. * Also known as T-stop. Assuming the ideal The f/number of a lens is defined by simple geometry (one length divided by another) so it assumes that the lens passes all of the light entering it. But no lens does: each interface between media of different refractive indexes causes a loss. Modern lenses are amazingly efficient so losses are in practice very small and, at any rate, losses are automatically compensated by through-the-lens metering. T-numbers are important in film industry, where TTL metering is not common.

So the T stop is an accurate corrected transmission reference for a particular lens as opposed to the theoretical maximum. Both use the same exposure scale”

By David Rasberry
from: http://www.scarletuser.com/showthread.php?t=882

jared
jared
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February 20th, 2010
Reply to  Romain

Super cool of you to put that up. Thanks.
Jared

photonashville
photonashville
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February 20th, 2010
Reply to  Romain

David,

Huge thank you! Very helpful explanations.

John

richardrock
Guest
February 19th, 2010

Nice interview, Jared. Keep up the good work.

jared
jared
Guest
February 20th, 2010
Reply to  richardrock

Thanks for the comment. It was a great day for DSLR.

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