Is the Panasonic 25mm a real f/1.4 lens?

Started Feb 17, 2014 | Discussions thread
Paul De Bra
Paul De Bra Forum Pro • Posts: 12,422
A general discussion of F versus T stop would indeed be interesting.

But of course the topic has come up several times already. There are still many people who think that the F stop really and truly corresponds to the amount of light a lens lets through whereas it is just about the dimension of the aperture. The F-stop also defines the maximum number the T-stop can be. But each lens element potentially absorbs some light so complex lenses will always have a T-stop that is measurably lower than their corresponding F-stop, perhaps more so with zoom lenses than with primes (although not "necessarily" so).

I can understand that it is confusing for consumers especially since the F-stop is published and the T-stop is not. People think that they will capture more light with an f/1.4 lens than with an f/1.8 lens but the definition of the F-stop does not imply that at all.

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