I've been primarily a Nikon shooter for all my digital SLR life; I started on film with some compact cameras and a Minolta X-700, but switched to Nikon starting with a D40, working my way up through the years to a D750 today. I love Nikon glass, I love the ergonomics, and I am very used to SLR photography and all it entails.
But after witnessing the steady rise in mirrorless camera popularity, I decided to start testing the waters with a Sony a6000. And one of the major benefits (at least in my usage) is that if you choose an APS-C system like the Sony a6xxx series, you can (in theory) have a more compact camera system that performs as well as larger SLR brethren.
In practice, you get what you pay for in terms of weight. The physics of light dictate that fast, good lenses will be pretty much the same size on whatever mount you use, and there are always some 'sweet spots' for compactness vs. performance on any kind of camera lens mount.
I was hoping the Sony 20mm f/2.8 pancake lens (SEL20F28) would hit that sweet spot for me on the Sony APS-C mirrorless system... but alas, it didn't.
tl;dr: The 20mm f/2.8 is a decent, extremely compact lens for Sony E-mount cameras, but it's performance is lackluster at best, and only marginally improved over the kit lens—but without zoom or stabilization. It's a little expensive for what you get, but it does turn an NEX or a6xxx camera into a pocketable affair, at least if you have large pockets!
First, an overview of what you're getting:
The lens has a thin but usable manual focus control ring. It's fly-by-wire, so the feedback is a little funky compared to lenses where focus is mechanically tied to the focus ring, but it works well enough with focus peaking when needed. The thinness of this lens is great for a compact walkaround camera setup, but it also makes getting it off the camera very slightly annoying, since you have to 'pinch' in around the free-spinning focus ring to get a grip on it. This might only be an issue for those with larger hands, though.
Speaking of thinness, how about a comparison to two other small E-mount lenses I have:
This lens is seriously compact; it's like Sony took the kit lens and sliced it cleanly in half. That's definitely the best attribute of the lens, and probably the reason you're reading this review. But size isn't everything—otherwise nobody would carry around two pound 35mm f/1.4 prime lenses!
But it does look great on the a6000:
You may notice the Borrow Lenses sticker on the side of the lens; I was a little leery of outright purchasing the 20mm, since it isn't a lens I could offload for a similar amount on Craigslist quickly, so I rented a copy for Labor Day weekend. I'm glad I rented the lens, because after using it for a few days, I found it's just not the right performance vs. compactness tradeoff for my style of shooting.
I could prattle on with words, but a picture speaks more eloquently:
"But wait," you say, "that picture doesn't look so bad!"
You're quite right—at least not when scaled down for web viewing or social media sharing. But I like to have more flexibility with my photos; and if a lens doesn't do much better than my smartphone in common scenarios wide open, I don't see the value (again, for me—it may be different for you!).
Let's zoom in and see where the problem lies—here's a 100% crop at f/2.8 (from the above picture) on the focal point—the chain on the right side of the swing:
Not horrible, but you can really see the performance compromise Sony had to make for this lens when you drop down to f/8:
Everything's sharper, and not just from the smaller aperture. Coma is better controlled, and the general 'haziness' across the frame (and especially bad out from the center) goes away—but only beyond f/4. And I really don't want an f/4 or f/8 lens, I want f/2.8 so I can pocket the camera and get a decent shot in any condition!
To give a more extreme point of comparison, here's the same FOV and 100% crop from my D750 and the Nikon 24-70mm f/2.8G lens:
Obviously, it's an entirely different optical system... and the setup weighs a couple pounds more... but if you're used to the latter image clarity (even when wide open at f/2.8!), and you're willing to compromise a bit, down to the level that, say, the Sigma 30mm f/2.8 Art provides, the 20mm at f/2.8 is a step too far. In similar conditions, I can get as good a shot from my iPhone's camera, albeit upscaled slightly. I don't want to lug around a one pound dedicated camera just to get images marginally better than the itsy-bitsy camera on my smartphone!
It is a decent lens. I would say as decent as the kit lens, without the ability to zoom and without OSS. For closer subjects, the bokeh is a little nicer than the kit lens, and if you stop it down a little, it passes up the quality of the kit lens at 20mm. I'm not disappointed with the quality, in fact I got a number of keepers from a walk around the St. Louis Zoo:
It's just that the quality isn't that much better than what I get with my iPhone, which I always have on me, and which fits even better into my pocket.
Therefore, I've decided to skip buying a copy of the 20mm f/2.8, and am (at least for now) sticking with my less-compact-but-noticeably-sharper Sigma 30mm f/2.8 Art. I switch to the kit lens when I do short video clips, but the Art is almost a permanent fixture due to it's compact size and solid performance on the a6000.
I didn't spend much time on focus performance, but that's because focus acquisition seemed similar to the 16-50mm kit lens and isn't really spectacular, but it's not horrible either.
Overall, it's like the kit lens, cut in half, and fixed at 20mm. If you want to get a feel for the 20mm lens, just pop the kit lens on, zoom in a tiny bit, and leave the zoom at that setting.
Buy the Sony 20mm f/2.8 E-mount lens on Amazon for $299.