What is It?
This may be one of the simpler reviews I've written, because the BCL-15 15mm f/8 body cap lens is quite a simple product. Olympus has simply put a small, three element (triplet) optical design into a body cap, then provided a lever controlled cover that can hide the elements (lens cap mode) or reveal them (shooting mode). No electrical contacts are in the otherwise all-plastic "cap."
Wait, how does it focus?
Manually. The lever that controls whether the lens is in cap or shooting mode can be moved from infinity to 1' (.3m) and has a click stop at hyperfocal distance. At the close focus distance there's surprisingly little depth of field (about 4", or ~.1m). At hyperfocal distance you should be okay from at least 5' to infinity. (Why the "should"? Depends a bit on how much we're going to magnify the print and then the distance we view it from.)
Wait, so how does it record EXIF data?
It doesn't. As I noted, there are no electrical contacts, and thus nothing to convey lens information to the camera.
How's it Handle?
Like a plastic lens cap with a small lever at the bottom.
Seriously, what's there to say? You need to learn which way is "closed" and which way is "infinity" (hint: hyperfocal distance is the strong click stop in the middle, and close focus is the extreme at which you can still see an image; if you see black, you went the wrong way and closed the cap), but that's about it.
The infinity click stop is somewhat sloppy on my sample, but still findable.
The interesting thing is that even the OM-D starts to be a pocketable camera (big pocket) with this lens cap lens mounted on it (see image, below). I'm sure some street photographers will fool a few people who think that they don't have a lens on the camera and thus can't take a picture, too.
While it would get a little expensive at US$50 a pop, I'm a bit tempted to put one on all my m4/3 bodies while traveling, just for the fun of being able to shoot nearly instantly from my travel bag.
How's it Perform?
Focus: the lens focuses as fast as you can move your finger.
Sharpness: The center is surprisingly quite good, even on the 16mp m4/3 bodies. If you get skilled enough to use the focus right and not depend upon lots of DOF, this lens is probably as good as the 14mm Panasonic at f/8 in the center. Triplet designs are like that: simple and center sharp.
The edges are soft, but not nearly as soft as I would have guessed. Moreover, with three simple "normal" lens elements involved, there's an organic nature to the softness: smeared a bit, but not distorted in ways you sometimes see with the asphericals. Corners are like my eyes sometimes are in the morning: not quite dialed in. Quite frankly, I've seen far worse corners on some much more expensive lenses with complex optical designs that were supposed to be "good."
Vignetting: Yeah, there's some modest vignetting, though again not as much as I would have expected. As it turns out, Olympus put an "aperture" inside this lens! Between two of the elements is a circular baffle that acts as the f/8 aperture. This actually explains why the corner issues aren't nearly as bad as one might have guessed they would be: the lens is essentially stopped down two stops!
Chromatic Aberration: Surprisingly low, especially given that the camera doesn't know there's a lens on and thus can't apply any in-camera correction. There's a tiny bit visible in extreme contrast situations, but most general shooting you can probably just ignore CA.
Distortion: I didn't bother to run the distortion tests on this lens (cap), as I don't see much linear distortion.
Overall, this lens cap is certainly in good kit lens range in terms of its optical qualities, maybe even better. A remarkable achievement for such a simple design and package.
Buy one. Simple as that. If you've got an m4/3 camera, buy one. Use it as your main body cap (though note that the BCL-15 should have its rear lens cap mounted when it's not on the camera, to protect the rear element).
Indeed, so many people have opted to buy this body cap lens that it's mostly sold out and some places that still have it are charging more than list price for it as I write this.
It's really a no-brainer purchase for those of you trying to go small and pocketable with your m4/3 system (e.g. GF5 and E-PM2 owners). These cameras actually do fit in most of my shirt pockets with this lens (cap) on them.
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