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

Started 10 months ago | Discussions thread
Steen Bay
Veteran MemberPosts: 6,415
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The t-stop also depends on the camera used
In reply to 007peter, 10 months ago

007peter wrote:

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

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.

We don't really know what the t-stop is for the lens itself. DxO's tests show the t-stop for a given camera/lens combination. For example, the t-stop of the 25/1.4 is 1.7 on E-M1 and 1.8 on E-M5. The article below shows how the t-stop of the same lens can vary considerably from camera to camera. The t-stop of the 25/1.4 could theoretically be 1.4 if it was tested on a camera without ' pixel vignetting'.

http://www.dxomark.com/Reviews/F-stop-blues

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