Panasonic 14 mm f/2.5 ASPH - Lenstip Review

Started Nov 17, 2010 | Discussions thread
Andrew Westlake Senior Member • Posts: 2,928
The 14mm's measured angle of view - 74 degrees at 2m, or 28mm-equiv.

OK, in this thread there's obviously some controversy over Lenstip's statement that the 14mm F2.5 effectively becomes a 31mm equivalent after software correction. To address this, I've just measured the angle of view of the lens.

Luckily, you don't need a PhD to do, this, just a tripod, a tape measure, a wall and a scientific calculator (that's the complicated one you get when you accidentally turn your iphone on its side). The method uses the simple trigonometry you hopefully learned at school.

I marked out a rectangle on a wall, which happened to be 2.4m x 1.8m in size. I then carefully aligned the camera so the distortion-corrected field of view was precisely defined by this rectangle. Finally, I measured the distance from the camera to the wall, which was more or less exactly 2m.

Now for the maths. Pythagoras gives us the diagonal of that rectangle as 3m, so half of the diagonal is therefore 1.5m. Half of the lens's angle of view is therefore defined as cotan(1.5/2), which gives the diagonal angle of view as 74 degrees (73.7 if you're being picky).

The lens's specified angle of view is 75 degrees, which obviously corresponds to a 28mm equivalent lens. As luck would have it, Pentax makes a 31mm lens, and if you look it up, its specified angle of view is 70 degrees. Clearly, the 14mm F2.5 is much closer to 28mm-equivalent than 31mm equivalent after distortion correction. It just has a wider field of view before correction.


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Andy Westlake

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