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

Started Feb 17, 2014 | Discussions thread
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Pixnat2
Pixnat2 OP Veteran Member • Posts: 4,177
DXO : t-stop is the effective way of measuring aperture.
3

Dheorl wrote:

Pixnat2 wrote:

I'm interested on a 25mm for my E-M1. We have two native 25mm now : a f/1.4 and a f/1.8 lens.

But there's some questions about the fact the Panasonic 25mm is a real f/1.4 lens :

That was in a very uncontrolled environment making it hard to tell how much was down to the camera making correction or just metering slightly differently. For example is the olympus does stronger vignetting correction on it's own lenses than the panny the metering in total will measure the scene differently.

True, but Robin takes real life pictures and they are much more important to a photographer than a wall or ruler picture to assess what a lens can do.

I'm very doubtful of that test. For instance different looking bokeh can cause the DoF to look different. If someone took a photo of a target with a front/back ruler like lenstip (and probably other review sites use) then we might actually be able to compare them accurately.

You're probably right about it.

Lenses t-stop should never match their f-stop.

The Canon EF 24mm f/2.8 IS USM, Canon EF 35mm f/2 IS USM, Canon EF 28mm f/2.8 IS USM for example have 1:1 t-stop f-stop.

DXO defines t stop well in layman's terms :

Thus, T-stop takes into account every reflection or absorption due to the lens. It can be considered as an effective (versus theoretical) way of measuring the aperture.

So I think it's worth watching their findings for each lens-sensor combination

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