30 Jun '13

What's the difference between the F Stop and the T Stop number?

A few weeks ago I was looking for the prices for the Samyang 24mm f/1.4 on Amazon, an affordable wide prime lens, when I noticed that just underneath tha lens, it was listed the following lens, the Samyang 24mm T1.5 lens, which is essentially the same lens but for videographers, with a better focus ring. But while it was pretty clear that the T1.5 was related to the max aperture for the lens, I didn't really understand why it was using a weird value (1.5) and why the T and not the usual "f".
The answer is simple: while the f number indicates area of the aperture of the blades, the T value indicates the amount of light that ends on the sensor of our cameras, and because light has to pass through the different pieces of glass in our lens (I didn't want to say lenses of a lens, it sounds weird to me), which reflect and/or absorb light, you will never get the 100% of light transmission, and the T number indicates the real amount of light that ends on the sensor. But as I'm terrible to explain how things works, and I doubt I will ever present an episode of MythBusters, maybe it's better if you just watch the video above, where Matt Granger explains, way better than me, what's the difference between the F Stop and the T Stop number.
(via ThatNikonGuy)

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