The compact Pentax Q system has received some buzz from nature photographers who appreciate the big 5x crop factor that it delivers to K-mount SLR lenses. The Pentax Adapter Q for K-Mount Lenses ($249.95 direct) makes it possible to mount any K-mount lens—from older 1970s model to the latest DA optics, to the Q7 and older Q camera models. It can give a short-telephoto 100mm lens a field of view equal to a super-telephoto 500mm lens, but you’ll have to manually adjust the focus of any lens that you attach.
The adapter is solidly built, with all-metal construction. It weighs in at 5.1 ounces, and measures 2.7 by 1.5 inches (HD). The rear of the adapter, which mounts to the Q, is narrower than the front, while the front has a mount for larger SLR lenses. There’s an aperture control ring on the lens barrel with marks at half-stop increments to narrow the aperture of the attached lens. This makes it compatible with newer lenses that omit physical aperture rings, as well as older lenses that have them. If you are using a lens with a ring, you’ll need to set the lens aperture ring to its narrowest setting and use the adapter’s control ring to adjust the iris.
There’s no tripod foot included, but Pentax does sell one for about $90. It’s the same foot that the DA* 300mm f/2.8 lens uses, and really is something that should be included with the adapter. If you’re using a lens with a tripod mount built in, it’s still best to use that as a mount point, but even a modest telephoto like the DA* 50-135mm is too front-heavy to use sans mount with the Q7.
We were curious to see how the Q7′s relatively small (compared with an SLR) 1/1.7-inch image sensor would fair with an SLR lens. You’re only using the very central part of the glass, which is often the sharpest area, but you’re still asking a lens to capture a 12-megapixel image using only a fifth of its surface area. For testing we opted for one of the sharpest Pentax lenses we had available, the legendary FA 43mm Limited f/1.9. When we tested the lens with the K-30 D-SLR it managed 2,000 lines per picture height at its widest aperture, and crossed the 3,000 line mark by f/4. We consider an image that is 1,800 lines or better to be sharp.
Mounting it to the Q7 reduced its sharpness significantly—again, it’s trying to eke out a 12-megapixel image using only a small area of the glass, where we were getting a 16-megapixel image with a much larger portion when pairing it with the K-30. At f/1.9 it scored a meager 400 lines, which results in a soft, blurry photo. Stopping down to f/2.8 improved things only slightly to 640 lines—at neither setting do we call photos useable, even for web sharing. Thankfully things get better at f/4. Here it managed 1,430 lines, just a tad on the soft side, and at f/5.6 it managed a printable 1,779 lines. To get the most out of this adapter you’ll want to use the best glass available, and shoot it at a narrower aperture. The sample images in the review were not shot using the 43mm, though; as this is ideally suited for extending the reach of longer lenses, I opted for a 1970s SMC 85mm f/1.8 lens when shooting in the real world. It’s an incredibly sharp lens when paired with D-SLRs and film bodies alike, and is still regarded as one of the company’s better short-telephoto optics. On the Q7 it delivered a field of view that is roughly 400mm, and as such really required a tripod for the best results.
The Pentax Adapter Q for K-Mount Lenses has a rather narrow audience. If you’re a Q owner who loves shooting at telephoto distances and has a stash of Pentax K-mount lenses, it’s likely on your radar. But be aware that it’s not the only game in town. There is a competing adapter available from Fotodiox that also offers aperture control. We haven’t tested it and can’t speak to in terms of build quality, but it’s only $30. And if you have a stash of SLR lenses that aren’t K-mount, you should look into an adapter that fits your glass—there are many available, at more reasonable price tags. Regardless of which adapter you buy, you’re going to have to stop down your lenses in order to get good results, and if you’re working with a lens that isn’t all that sharp to begin with, you shouldn’t expect great results.
Copyright © 2012 Ziff Davis, Inc