# Can somone further explain T-Stops to me?

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### #1 Nick Castronuova

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Posted 26 March 2008 - 11:30 AM

Sorry, I know. Basic question. But I'm having trouble finding a simple, straight answer. I understand that Zoom lenses have T-Stops, and it releates to the amount of light that is lost going through all the parts of the zoom lens.

But how do you take this into account when lighting and in relation to the F-Stop? Basically, when shooting, how do I go about T-Stops?

Nick
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### #2 John Holland

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Posted 26 March 2008 - 11:59 AM

Its not as difficult as you seem to think . If your light meter says F4 , just set your lens be it zoom or a prime to T4 . and thats it .
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### #3 John Sprung

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Posted 26 March 2008 - 07:43 PM

Use T-stops for exposure, and f/stops for depth of field.

They'd be identical if there was no light loss at all in the glass. For lenses with only a very small amount of light loss, the lens makers just give us f/. If there's enough light loss to make a difference, they give us both.

-- J.S.
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### #4 Daniel Sheehy

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Posted 26 March 2008 - 09:46 PM

The F-stop is a purely mathematical construct.
The T-stop is that same mathematical ratio, adjusted to reflect the actual amount of light being transmitted.

So for lighting purposes, just use them as the same as each other. The only time you actually need to think specifically about the F-stop is if you are trying to do something specific with the depth of field.
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### #5 Chris Keth

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Posted 27 March 2008 - 02:48 AM

It's quite simple:

F/stops are ratios of certain parts of the lens. They tell you, theoretically, how much light is passes through the lens. It's like when you would do physics in highschool and disregard air resistance for simplicity-sake.

T/stops are an actual measurement. A known quantity of light enters the lens and the light that comes out the other end is measured. This is more like university physics where you take into account air resistance, and barimetric pressure for that matter and other things since they all slightly affect the results.
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