Let’s get this out of the way first: I know these lenses were designed for different mounts, different formats and even different recording media. Still, it’s not apples to apples; it’s more like apples to pears or peaches to nectarines. The Pentax and Olympus 75-ish mm lenses are the same price, the same-ish focal length, the same maximum aperture, roughly the same size, similar build quality, and oh yeah, they both take pictures when you stick them on a camera and point them at stuff.
The Pentax FA 77mm Limited is one of the best AF lenses ever made and it has a devoted following of Pentaxians who wait year after year for Pentax to release a “full-frame” DSLR to put it on. Some Pentax fans even adapt full-frame Canon DSLR’s just to use this lens. I can’t say I understand the thinking there since Canon sells a silent-focusing 85mm f/1.8 for about half of what Pentax charges for its 77. Perhaps it’s the pixie dust. The Pentax FA Limiteds are built like no other AF lenses. They are compact, metal, and heavy. Even without taking a picture you can tell they are special. That specialness doesn’t stop once you start taking photos. The 77 is sharp from wide open and has beautiful rendering. Stop down a little and you’d be hard-pressed to find a technical flaw. I suppose I should mention that the focusing is slowish and loud, but I don’t care. Try this lens for a day and I guarantee you won’t care either.
I’m renting the Olympus 75mm, so I don’t have very much personal experience with it. It’s very new, but already has an excellent reputation. For micro 4/3, there is no AF competition for this lens. The build quality is better than any other micro 4/3 lens I’ve ever used (I’m guessing that the Voigtländers are built better). However, it’s not as well-built as the Pentax. I’m sure they are both perfectly reliable, but in terms of “feel” it’s not even close. The Pentax wins. Also, how about that size difference? I said they were close, but the Olympus is significantly bigger than the Pentax. One of the huge advantages of micro 4/3 is that the lenses are so much smaller than their APS-C or 35mm equivalents. How is it that the Pentax, which was designed for a 4x larger sensor is so much more compact than the Olympus? Ok, it’s not that much of a mystery: the Olympus has a more complicated modern design and internal, silent focusing.
I haven’t yet had time to take any “real” photos with the Olympus, but I found this comparison too interesting to pass up. I compared the Olympus 75mm on an OM-D and the Pentax 77mm on a K-7. That’s 16MP vs 14MP and 150mm vs 115mm equivalent FOV. I used contrast-detect autofocus for both cameras and took all pictures hand-held because that’s how I take most of my photos in real-life. Here are a few 1:1 comparisons for you to peruse:
The differences are small, but it’s not hard to tell the Olympus is sharper than the Pentax. Surprisingly, they both had about equal purple fringing. The Pentax is known for being pretty bad at fringing and micro 4/3 lenses are software-corrected for fringing. For me, the differences between the lenses come down to issues with their respective formats. DOF control between micro 4/3 and APS-C is essentially the same. Any difference between the two can be easily mitigated. Full-frame does offer more control of DOF but there is not yet a full-frame Pentax DSLR, so the point is moot.
I’ve been shooting exclusively micro 4/3 lately, so going back to the K-7 was interesting. The autofocus speed was about the same between the OM-D and the K-7 with their 75mm-ish lenses attached, but the contrast-detect autofocus of the OM-D was way more accurate and repeatable than the phase-detect system in the K-7. The auto focus design of DSLR’s is inherently dependent on calibration and thus susceptible to front or back focus errors. Contrast detect focusing measures whether the actual image data is in focus. There is a speed advantage to phase-detect sensors, but that gap is closing fast. I had to switch to the glacial live-view contrast detection AF mode on the K-7 to get these samples to focus accurately. It’s not all bad news for the Pentax, though. I’ve yet to use a camera that feels better in hand and has better control placement than the K-7 (and the identical K-5, K-5II etc).
What’s most interesting to me is that the differences between the two just don’t matter much. If the lens is good enough then the variables that pop up when we are out shooting are going to dwarf any tiny differences in image quality between two excellent lenses. I threw in some shots with the Olympus 45mm as well. When you get closer to the subject to match the subject size to the 75mm shot, the DOF is roughly the same. So much unnecessary internet-blood has been spilled by people arguing over differences in DOF between different lenses and formats.
Since this is a “battle” I must now choose a winner… The winner is the Olympus, but I reserve the right to change that verdict after shooting with it in the real world (until I have to ship it back). Don’t throw your Pentax up on ebay just yet, though. The 77/1.8 is still an amazing lens that can be used to produce images with a signature look. The slightly older design of the 77/1.8 means it can’t compete on sharpness with newer lenses, but it has just the right blend of character and technical perfection. In fact, I better stop writing about it now because I might end up changing the verdict.
Update: I removed the 100% crop comparisons with both lenses mounted on the OM-D because I messed up the manual focusing. The full images are still available for comparison, but keep in mind that the focus point is different between the two shots.