Olympus 12-40mm f/2.8 vs. three primes

This is my final test of the Olympus M.Zuiko 12-40mm f/2.8 “PRO” lens.

I have three prime lenses:

Olympus 17mm f/1.8
Panasonic “Leica” 25mm f/1.4
Olympus 45mm f/1.8

How do they stack up against the zoom lens?

For this test, I pointed the camera at a point midway between the center and the top-left corner. My reasoning for doing this is that, while it’s not important to test the extreme corners when using a lens wide open (nor is it reasonable to expect the extreme corners to be sharp when a fast prime is used wide open), neither do you want to test the exact center of the frame because your subject is not always going to be in the exact center of the frame.

I took a picture of a USAF 1951 test pattern on my computer monitor.

The conclusion is that, for all three prime lenses, the zoom at f/2.8 (wide open for the zoom) is sharper than the prime wide open, but when the prime is stopped down to f/2.8, it’s sharper than the zoom. But I think that all three primes are sharp enough to use wide open, and the zoom is sharp enough to use wide open (being even sharper than the primes wide open). The differences in sharpness are pretty small and you have to be pixel peeping at 100% to see the difference. All four lenses tested performed very well.

I have the following additional observations:

17mm f/1.8: I don’t understand why there’s this belief on the internet that this is not a sharp lens. It seems very sharp to me.

25mm f/1.4: This lens has quite a bit of purple fringing. This has always been a problem when using Panasonic lenses on Olympus cameras, and my recommendation is that, if you own an Olympus camera, you should avoid Panasonic lenses. Even the lenses co-branded as “Leica” have this problem. Definitely not up to the standards of a real Leica!

One can argue that you can make the purple fringing inconspicuous by using the Defringe slider in Adobe Camera Raw, and that in the real world you would be using the lens for portraits and not for taking pictures of a test chart on a computer monitor. And this is certainly true, but all things being equal, I’d prefer a lens that didn’t make these purple fringes. Too much fringe removal in Adobe Camera Raw leaves behind artifacts that are noticeable when the photo is viewed at 100%. For example, we saw that there were halos caused by lateral CA correction when I tested the extreme corner resolution of the 12-40mm.

12-40mm @ 40mm: According to internet tests, this lens is supposed to be weakest at 40mm, but it seems plenty sharp to me, even wide open.

45mm f/1.8: I would say that this lens is the closest to optically perfect of the four lenses I tested. It’s the sharpest wide open and has the least fringing. However, this is not surprising, because it’s a lot easier to manufacture a sharp telephoto lens than it is to manufacture a sharp normal lens or a sharp wide-angle lens.

View the test photos below.

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