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

Started Feb 17, 2014 | Discussions thread
Dheorl Veteran Member • Posts: 3,781
Re: Agree.

Pixnat2 wrote:

EarthQuake wrote:

Pixnat2 wrote:

007peter wrote:

Hi Peter, thanks for your answer

I share the same thought as you (for the most part). However, you must keep your Expectation Realistic & Reasonable. A slight 0.3ev lost in T-Stop is to be expected. AFAIK, no lens live up to their T-Stop claim (or very very few do). Most manufacture measure them under the best LAB CONDITION, so in everyday "Real World", a slight 0.3ev lost isn't outrageous.

For example, the DXO Tested T Stops are:

  • 2.0 T-Stop for Panasonic 20mm F1.7 (II) | -0.3ev
  • 2.1 T-Stop for Panasonic 20mm F1.7 (I) | -0.4ev
  • 2.2 T-Stop for Olympus 12mm F2 | -0.2ev
  • 2.0 T-Stop for Olympus 45mm F1.8 | -0.2ev
  • 2.0 T-Stop for Olympus 75mm F1.8 | -0.2ev

Yes, I've seen it. Panasonic primes seems to be consistently 0.3ev darker than the claims, while Olympus 0.2ev.

Based on DXO results, I would say Olympus is more consistent with narrower gap between Lab Tested "claimed" vs real-world tested results. It would surprise me if the new Olympus 25/1.8 is tested exactly at 2.0 T-Stop.

Robin Wong seems to think that it's actually brighter than its claims. It would be a good surprise if DXO confirms it (though I doubt it).

Either way, I wouldn't worry about it. Since Olympus is the cheaper of the two, I just buy it over Panasonic.

That's my thinking now, though I like the pictures I've seen with the Panasonic. I think I'll buy the Olympus, but I'm curious about the diffrences between both.

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Fstop and tstop are two different concepts, Fstop is the physical size ratio of the aperture to focal length, tstop is how much light the lens lets through, and varies but the type of glass elements used, no lenses have a 1:1 tstop to fstop ratio nor are any manufacturers "lying" about tstops when they list fstops. This is why cine lenses are rated as t-stops not f-stops.

Yes, I'm aware of that, though some lenses have 1:1 Tstop for Fstop :

Then canon are misrepresenting the f-stop of the lens, DXO are measuring it wrong or rounding errors are coming in to play.

Transmission can be influenced by many things like elements and coating as you said, but it could be influenced by the actual aperture of the lens too.

If it was only this DXO measure, It wouldn't have raised the question. But Robin Wong (I think he is honest) and other threads seems to find that the Panasonic is a bit darker than it claims.

Moreover, I never imply someone is lying, I'm just curious.

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