Why isnt the PL452.8 the reference lens for testing m43?

Started May 25, 2012 | Discussions thread
Adventsam
Veteran MemberPosts: 4,983
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Re: Therefore?
In reply to Andy Westlake, May 25, 2012

In theory on a GH2 the results with the 45mmPL2.8 could be better still? maybe that's just what I'm seeing, an ultra sharp sensor with class leading DR and sharpness all adding together to provide superb resolution.

Many thanks anyway, what an interesting thread this has turned out to be as per usual.

Andy Westlake wrote:

Adventsam wrote:

Andy, your test with the E-3 and 50mm showed the 50mm lens to be inferior to the 45mmPL, can you explain why that was?

Of course. First though, I'll have to correct your observation to something more technically-correct; our sharpness tests results show 50/2 on L10 > 45/2.8 on G1 > 50/2 on E-3. This is simple to explain.

Our lens testing methodology - like most around at the moment - doesn't test the lens in isolation, but the lens on a camera. This means that the overall measured MTF is determined both by the lens and the camera's anti-aliasing filter. You can see this by comparing the ZD50/2 on the L10 and the E-3, which had unusually weak and strong anti-aliasing filters respectively:

http://www.dpreview.com/lensreviews/widget/Fullscreen.ashx?reviews=32,33&fullscreen=true&av=2,2&fl=50,50&vis=VisualiserSharpnessMTF,VisualiserSharpnessMTF&stack=horizontal&&config=LensReviewConfiguration.xml%3F1

You need to run through the aperture settings to see the differences properly. But essentially the E-3's AA filter prevents the lens/camera combination reaching the same sharpness levels as it does on the L10 at its optimum apertures.

What this demonstrates is that the camera body has an effect on lens test data, and that the E-3 would have been a poor choice for reviewing Four Thirds lenses. Obviously, this leads to the smart next question - how do we know that the measured differences between the 45/2 on the G1 and the 50/2 on the L10 aren't just down to the camera body?

The way to answer this, of course, was do do some quick internal testing of the 50/2 on the G1. As it happens the G1 gave practically identical MTF results to the L10 with the 50/2 macro, strongly suggesting that the L10 and the G1 used basically the same anti-aliasing filter, despite the former being 10MP and the latter 12MP. Here's a screenshot at F6.3:

This data isn't publicly available (as we didn't rerun every test and every aperture setting), but here's the screenshot showing the 45/2.8 compared to the 50/2 on the same camera body under the same conditions:

I hope this clears things up for you.

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Andy Westlake
dpreview.com

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