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#1 L K Keerthi Basu

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Posted 29 June 2005 - 09:55 AM

I have a very basic doubt on f-stops calibration to the T-stops. We are taking exposure meter readings in the f-stops ,while cutting the exposure in the lens it is T-stops. How their calibrating the f-sops to the T-stops in the lens. I know the difference between the T-stops and the f-stops. Please kindly forgive me if I have asked a silly question.

L.K.Keerthibasu
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#2 Sam Wells

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Posted 29 June 2005 - 10:31 AM

I'm not quite sure what the question is.

If you're using T stops marked on your lens, then you're effectively measuring T stops with your meter.


i.e. actual amount of light transmitted by the lens.

-Sam
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#3 Dominic Case

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Posted 29 June 2005 - 06:35 PM

Your meter measures the amount of light and tells you the exposure required.

Your lens is calibrated for exposure in T-stops: it's the actual amount of light that usefully passes through the lens. So you simply set the exposure meter reading on the T-stop scale of the lens.

F-stops are precise for depth of field calculations as they relate to the diameter of the aperture: but they ignore light losses, so aren't so precise for exposure.

The difference between the two (f & T) is a property of the particular lens, and may only be a fraction of a stop, or a little more. But if your lens has - say - one third of a stop difference between f-stop and t-stop, that is more or less a constant over the range.
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#4 oscar jimenez

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Posted 01 July 2005 - 09:49 AM

f STOP only takes account of mathematical and geometrical calculation of light transmission at a given aperture setting an F stop is the number that is derived by divinding the focal lenght of the lens by its effective aperture, that is the diameter of the beam of light which can pass through the lens at a given setting and it is based on square root of 2 ( aprox 1.4 ). T stop is exactly what physically lens transmision capabilities of lens ellements tested in an optical bench T stops ( t from "true stops". Use always the T stop markings, that's what it is the real thing( mostly painted in red in the lens barrel ) ie. Angenieux 12-120 has the two scales ( white f stops, red T stops ).
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#5 John Pytlak RIP

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Posted 01 July 2005 - 10:00 AM

Use T-stops to set exposure, F-stops to calculate depth of field.

As noted, T-Stops take the lens transmission into account. The correlation of the two depends on the particular lens.
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