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T-Stops question?


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#1 Joe Hemsani

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Posted 25 July 2006 - 04:53 PM

Hello, I have a question about T-Stops.

Why are there T-Stops in numbers such as T/1.7, T/1.9, T/1.3, T/2.1 if those numbers arent even thirds of a T-Stop. What does this mean??

Thank you!
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#2 Adam Frisch FSF

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Posted 25 July 2006 - 05:00 PM

You will find that these stops are only there to describe the lowest setting and is a way for manufacturers to inform us about how fast their lens is at the widest aperture. Hence a T1.3 lens is slighly faster than the 'normal' setting of T1.4 and something they want to brag about.
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#3 Stephen Williams

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Posted 26 July 2006 - 03:55 AM

. Hence a T1.3 lens is slighly faster than the 'normal' setting of T1.4 and something they want to brag about.


Hi,

That extra 1/3 stop can be useful at times!

Stephen
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#4 Joe Hemsani

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Posted 01 August 2006 - 11:13 PM

thanks I just wondered why thery did it but now I know!!!111

best regards
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#5 Chris Keth

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Posted 01 August 2006 - 11:22 PM

A t-stop is just a ratio of the focal length to the iris opening. It doesn't have to be expressed in whole, half, or third stops.
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#6 Stephen Williams

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Posted 02 August 2006 - 02:02 AM

A t-stop is just a ratio of the focal length to the iris opening.


Hi,

You are referring to F stops. T stops are corrected for light transmission.

Stephen
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#7 Matt Pacini

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Posted 02 August 2006 - 06:18 PM

So this begs the question; why aren't ALL lenses rated as T-stops?
It's obviously the only accurate measurement, yet all still photo lenses are in F-stops.
Why wouldn't the entire industry switch over?

MP
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#8 Stephen Williams

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Posted 03 August 2006 - 02:30 AM

So this begs the question; why aren't ALL lenses rated as T-stops?
It's obviously the only accurate measurement, yet all still photo lenses are in F-stops.
Why wouldn't the entire industry switch over?

MP


Hi,

Most SLR still cameras have built in light meters so it does not matter what the F to T stop relationship is.

For motion picture work lenses need to match both in color and exposure throughout the set.

Stephen
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#9 John Pytlak RIP

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Posted 03 August 2006 - 10:37 AM

A separate T-Stop calibration becomes more important with lenses that have significant light losses (e.g., complex zoom lenses with many elements, older lenses that had more internal light loss due to flare). A modern prime lens with multicoated elements is unlikely to have much more than a 1/3 stop difference between the f/stop and T-Stop calibration, which is well within the latitude of the film.
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