# What is mFT FoV?

Started 4 months ago | Question thread
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 Re: Anders: some measurements In reply to Steen Bay, 3 months ago

Steen Bay wrote:

gollywop wrote:

Anders W wrote:

gollywop wrote:

Anders W wrote:

Anders W wrote:

gollywop wrote:

Anders W wrote:

gollywop wrote:

Whoop, Anders, your link to the means for testing angle of view doesn't work. Can you try again?

thanks,

Don't know what went wrong with that. But I corrected the link by editing my previous post. It should work better know (at least it did when I tried) but here it is again just in case:

http://www.panohelp.com/lensfov.html

Well, Anders, it seems my hypothesis (and hope) was wrong. The nominal focal length appears to apply to the uncorrected, not the corrected, image. I did the measurements according to the link you give above. I did them twice, once fairly rough and ready and again much more carefully, but there's no substantive difference; they tell essentially the same story with the 12-35 at 12mm:

The corrected AoV is about 68.67° for an EFL of 26.35

The uncorrected AoV is abut 73.33° for an EFL of 24.23.

So, the 12-35 appears to be a 12mm lens only if you put up with the distortion. It is otherwise a 13 mm lens (at least after ACR does whatever it does -- which, I suppose, is effectively what the OOC jpeg would be also).

Well that's a pity as far as the 12-35 is concerned. But you also have my test of the 20 and Lenstip's test of the 14, where things worked out differently (FoV after correction equals the specs). So my preliminary conclusion, provided your measurements are correct, is that Panasonic has cheated a bit when it comes to the specs of this particular lens rather than it being generally the case that the specs refer to the uncorrected image.

Hold on a second here. The horizontal FoV at 24 mm EFL is 73.7 degrees when the aspect ratio is 3:2. With an aspect ratio of 4:3, however, it is 71.6. So the FoV after correction is still smaller than it should be but the FoV before correction bigger. The EFL at 68.67 is about 25.3.

Ah, yes. I'd forgot about that. But the story is even a bit better: I refined my measurements, and the corrected image has an AoV of 69.03°, which puts things a bit closer to 25. So, it appears they've shaded things slightly, but only slightly.

Perhaps Panasonic simply rounded downwards from 12.5.

Yep, that does appear to be the case. I was able to make a corroborating test. In my experiments dealing with the 12-35 edge sharpness (reported here), I had made a series of shots using the 12-35 at 12 mm and an identical set of shots using the 12-50 at 12 mm. The FoV of the 12-50 at 12 mm is slightly, but noticeably, larger (both in the corrected images). It would appear that the Oly specs are correct but the Panasonic is a bit "pulled."

Should be possible to fix that with a firmware update if the uncorrected EFL is close to 23mm.

Interesting notion.  How does one go about attempting to have such a firmware update made?

--
gollywop

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