The Lomography New Petzval Lens is one of the oddest new products of the year, both in concept and design. Available in brass ($599) or black ($699), and funded via a Kickstarter campaign, the Petzval is based on an 1840s lens designed by Hungarian mathematician Joseph Petzval. It's got a steampunk look to it—especially if you opt for the less expensive brass version—complete with a knob on the side that's used to adjust focus. It can be had in a Canon EF or Nikon F mount, and you can always use it on a mirrorless camera via a mechanical adapter.

The Petzval is big and on the heavy side. It measures 4.5 by 3.7 inches (HD) and weighs 1.5 pounds. I paired it with a Nikon Df and found that it balanced well with that bulky camera; I also shot it with a slimmer 35mm Nikon F3 and felt that combination was a little front heavy. Its focal length, which is oddly not part of the lens name, is 85mm and the maximum aperture is f/2.2. There's a small knob on the left side of the lens barrel that turns to adjust focus. A focus scale is printed on the top of the lens, right ahead of the slot in which you slide the Waterhouse aperture plates. The lens can focus as close as a meter (3.3 feet) and supports 58mm front filters—you'll have to unscrew the metal hood to use them, though. A slide-on metal lens cap is included, matched to the color of the lens, as is a leather carrying pouch, and a book that highlights the history of the Petzval design. Everything ships in an attractive display box—Lomography has put a lot of care into the packaging and design of this one.

If you're only aware of modern lenses with built-in diaphragms to control the amount of light that passes through, the Waterhouse system takes some explaining. Instead of an internal aperture controlled by a ring or electronically, the Petzval uses a series of removable plates, each with a smaller diameter circle, to cut down the light that passes through to the sensor. Plates for f/2.2, f/2.8, f/4, f/5.6, f/8, f/11, and f/16 are included. There's also a solid plate that you can install when storing the lens, and a set of three plates with noncircular apertures (a teardrop, a hexagon, and a five-pointed star) that will add those shapes to the highlights in the out-of-focus area of an image. A blank "do it yourself" plate is included, but you'll need metal cutting tools to take advantage of it.

I found that the plate system had its pluses and minuses. I liked the ability to drop in the shaped plates—I shot a bit with each of them, and really enjoyed the effects I was getting, especially with the hexagon aperture. I was able to pick out stars in the backgrounds of a few of my shots when using the star plate; I was working in the daylight and looking for branches and other natural backdrops, but if you're using the Petzval for night portraits lit by streetlamp, lights in the background will take on the shape of those aperture plates.

On the other hand, in order to take the lens out and have the ability to adjust the light coming in, I found myself carrying a nearly a dozen little metal plates. The included leather carrying pouch was helpful for keeping them straight, but if it moved around in my camera bag they fell out. You're better off using a ziplock baggie; it isn't as elegant a carrying device, but it's the most practical way to keep from losing any of the Waterhouse aperture plates. The other issue with the plates, at least at first, is that they're a bit too tight to slide easily into the lens. After a few insertions and removals enough material flaked off from both the lens and plates to alleviate that, but I was left with noticeable debris inside the lens. Thankfully cleaning the internals is a simple matter of unscrewing the front element and blowing out the interior with a compact air blower. After just a few changes all of the plates slid in and out of the Petzval without issue.

Normally we use Imatest to check the sharpness of a lens using an SFRPlus test chart. Modern lenses are designed to focus on a flat field, parallel to the front element and image sensor. But the Petzval design results in a field that's noticeably curved. That's part of the reason for its unique look, but it delivers artificially low results in our sharpness test. I did shoot a sequence of shots using aperture plates from f/2.2 through f/8 with the 36-megapixel Nikon D800 to get an idea of the center sharpness of the lens. We like to see lenses hit a center-weighted average of 1,800 lines, but that metric doesn't translate well due to the Petzval's field curvature.

At f/2.2 the very center of the lens shows 1,953 lines, but that drops off quickly; moving just slightly away from the center shows scores that are around 900 lines. Imatest calculates that the average score across center third of the frame (completely ignoring the outer two-thirds, which are out of focus) to be about 750 lines. Swapping in the f/2.8 plate shows a dead center score of 2,327 lines and a center-third average of 934 lines. There's a bit more surrounding the center that's sharply in focus, which gives you a little bit of leeway with framing.

At f/4 you've got a lot of leeway. The center-third of the frame records 2,070 lines; the curved field of focus causes the outer parts of the frame to score low on our test, but at this aperture you'll be able to more comfortably frame subjects towards the outer part the frame and have them sharply in focus. At f/5.6 and f/8 the sharpness continues to increase; the center-third scores 2,443 lines at f/8. A wider depth of field reduces the effects of the field curvature, and the narrower aperture does what it does with most lenses—it makes the image sharper. Regardless of which aperture you use, the Petzval shows a little bit of pincushion distortion—about 1.5 percent. That causes straight lines to curve slightly inward; it would be an issue if you were using the lens for architectural imagery or other work that required precise reproduction, but for portraits it's nothing to worry about.

These scores translated to what I experienced in the field. I took the Petzval out and shot with it before running any numbers, in an attempt to get a more natural feel for how it performed. I was happiest with the lens at f/4—there I found the balance of sharpness, depth of field, and wacky bokeh to be just about perfect for my tastes. The hexagon aperture plate is listed at f/3.9, and I ended up using that more than the circular f/4 plate.

To get the most out of the Petzval, you'll need to take some care in framing. When I was working with the f/2.8 plate I found that it was very difficult to get a sharp view of my subject on the F3's focus screen when it was framed to the right or left of the frame. When working with a digital camera with Live View and magnification I managed a bit better, but was still wanting for some more crispness. When I framed my subject at the center of the frame at f/2.2 and f/2.8 I was much happier with the results; this isn't normally how I shoot a subject, but the Petzval made me rethink that approach and I got a few results that I really loved, including one that's destined for a frame.

At f/4 the lens handles more like a modern optic. There's enough sharpness and depth of field that I felt comfortable placing subjects at the edge of the frame, and, under the right conditions, the bokeh was just as swirly and wonderful as at wider apertures. That brings up the other aspect of effectively getting the Petzval look—picking your spots. I received the lens in the winter, and sought subjects with barren tree branches in the background. I also took a few shots against a flat blue sky to see what would happen—the subjects were drawn with a noticeably vintage look, but that's not why you buy this lens. Bare branches, fall foliage, city streetlamps, and cloudy skies will all play up the bokeh that the lens is capable of producing. You'll want to take care to make sure your subject is far removed from the background (if you're working with a model or shooting formal portraits, play around a bit with that—it won't take long to get the hang of it); the distance between yourself and subject should come based on the Petzval's field of view. Given the right location you'll likely want to take a few steps back and capture more of the background for a more dramatic shot.