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

Started Feb 17, 2014 | Discussions thread
David Kieltyka
David Kieltyka Veteran Member • Posts: 5,048
Re: A general discussion of F versus T stop would indeed be interesting.

Paul De Bra wrote:

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.

Using the Sony A7r over the past month with a whole bunch of different lenses, in Av mode with a fixed ISO, I've become used to stopping down an f/1.4 lens to f/2 and seeing little or no change in shutter speed or in the histogram of the resulting photo. Typically the image corners brighten at f/2 but the image center darkens...the two seem to largely cancel each other out in terms of overall exposure.


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