The Funleader x Brightin Star XSlim-M 28mm F2.8 ($358.99) is one of the most intriguing M-mount lenses in recent memory thanks to its exceptionally small design, striking black paint finish, and unique optics that bend the field of focus. The pancake prime is a great value too, especially compared with first-party Leica entries like the Elmarit-M 28mm F2.8 ASPH. ($2,795). The XSlim-M doesn't strive for optical perfection like its Leica counterpart of course, but it's still worthy of our Editors' Choice award for photographers who prefer artistic flair over clinical excellence.

The Silver-Dollar Pancake Lens

The XSlim-M is undersized even by M lens standards. Leica M cameras don't have any sort of autofocus or electronic contacts, so lenses for the platform are manual-focus and lack optical stabilization as a rule. These characteristics and a relatively small lens mount make the 28mm's diminutive 0.9-by-2.0-inch (HD) size possible. Even more impressive, however, is that the lens protrudes just 0.3 inches when you mount it on your camera body since some parts sit internally. Funleader markets it as a pancake lens, but I'll go further and say it's a silver-dollar pancake—it's that tiny.

(Credit: Jim Fisher)

The lens is a little heavy for its size at about 4.4 ounces. Materials play a part: The barrel is brass, a denser alloy than the more common aluminum. The brass material also means that its body is painted, rather than anodized like on an aluminum lens. Over time, the paint should wear a little thin to show gold flecks of color. The various markings are also painted.

The brassed camera look is popular among Leicaphiles, even if it has fallen out of fashion for current cameras—the black M10 and M11 are anodized. For testing, I matched the XSlim with an older model, an M (Typ 240) that I've used for 10 years. The camera's black paint finish is more matte than the XSlim's, but I still think they look great together. Of course, I'm biased since I've grown attached to my Typ 240 over the last decade.

(Credit: Jim Fisher)

M-mount lenses are highly adaptable, so you don't necessarily need a Leica to use them. With the appropriate adapter (basically a lightproof metal spacer), you can pair the lens with nearly any mirrorless camera. Funleader offers your choice of a Canon EOS R, Fujifilm X, Leica L, Nikon Z, or Sony E adapter as a $10 add-on with the lens. If you shop around, you can easily find one for Canon EOS M or Micro Four Thirds cameras, too.

(Credit: Jim Fisher)

Going the other direction, the XSlim also works with M-mount film cameras. I didn't find the time to shoot any film with the lens, but I put it on my 60-year-old Leica M3 to check compatibility and its rangefinder-coupled focus worked fine. I noticed a bit of a jump in the focus patch when I tried the lens with a 1970s-era Leica CL, so take caution if you use it with a similar body (or a Minolta CLE). To be fair, Funleader promises compatibility for the M series cameras only, not the CL. Unfortunately, I don't have access to any non-Leica film bodies like the Konica Hexar RF, Voigtlander Bessa, or Zeiss Ikon ZM to check the focus coupling on those.

(Credit: Jim Fisher)

A Unique Entry in a Crowded Field

The XSlim-M is a collaboration between a pair of relatively obscure brands: Funleader and Brightin Star. Funleader handles distribution and many design aspects (including the packaging and lens exterior), while Brightin Star is in charge of the optical design and manufacturing. Funleader has made a name for itself with fun lo-fi lenses like the Caplens and also retools old Contax G rangefinder lenses for Leica M bodies. Brightin Star is a newer brand; it recently made news with the widest-ever rectilinear full-frame lens, a 9mm F5.6 for mirrorless cameras. Collaborations are relatively rare in the photo world, but I'm glad that this one came to fruition. Just note that you might see this lens with only Brightin Star branding at some stores.

As for alternatives, there are far too many 28mm prime lenses for M mount to list here. Among small, similarly wide options, the aforementioned Elmarit-M 28mm F2.8 ASPH. produces clinical results. Leica also sells the Summaron-M 28mm F5.6 ($3,095) as part of its Classics line; its 1950s-era optical formula leans into a soft, low-contrast look.

(Credit: Jim Fisher)

If you can't handle Leica prices, the TTArtisan 28mm F5.6 offers similar aesthetics to the Summaron for $368. Voigtlander markets the Color-Skopar 28mm F2.8 Type I ($699) with a vintage-style barrel, as well. I haven't tried the Voigtlander, but its aspherical optical formula suggests that it creates photos with a sharp, modern look. I have tested the Lomography LC-A Minitar 32mm F2.8 ($249), however, a pancake with plenty of character and rangefinder coupling.

I must also mention MS-Optics, a one-man lens boutique that makes the similar Apoqualia 28mm F1.7 MC ($1,000) and has developed a cult following among photo enthusiasts. The XSlim-M and Apoqualia share many design aspects, so I think it's appropriate to consider the former a budget-friendly alternative to the latter. Both feel crafted, and not like just another lens off an assembly line.

(Credit: Jim Fisher)

Quality Mechanical Controls

The XSlim-M handles fairly well despite its size. That's in large part because its focus lever is easy to find by touch and provides a real sense of control. The manual focus action has enough resistance for precision but is smooth enough that I can use just my index finger for adjustments.

The aperture control is a little more finicky. It rings the front element and sits deep enough that you need to take some care to move it. The ring turns smoothly without detent stops from f/2.8-16. I find it easiest to set the f-stop from in front of the lens since doing so allows me to use two fingers and actually see what value I'm selecting. Inadvertent changes to the f-stop are nearly impossible, but this mechanism could still use improvement. I wish it were just a bit more pronounced.

(Credit: Jim Fisher)

I didn't use filters with the XSlim because I don't have any in its oddball 25.5mm size. I did try to adjust the aperture ring with the included screw-in lens cap attached, however, and that proved a very clumsy experience. I'm not a fan of the lens cap overall, since it seems easy to lose and requires precise positioning before it threads in.

(Credit: Jim Fisher)

Like most M-mount lenses, the XSlim-M doesn't focus very close. It's limited to 27.6-inch (0.7-meter) focus, the same as what most M cameras support for coupled focus. You need to get a close-focus helicoid adapter for a mirrorless camera or an extension tube for an M body if you want better macro performance.

A Wholly Artistic Rendering

I used the XSlim-M with a 24MP Leica M (Typ 240) for both lab tests and real-world photography. It turned in very good results for a 24MP sensor (2,500 lines wide-open) when I evaluated SFRplus test chart results with Imatest software. Stopping down the aperture lifts the score into the excellent range (2,700 lines at f/4-11). A test chart score doesn't nearly capture the lens' overall picture quality and character, however.

(Credit: Jim Fisher)

Most uniquely, the XSlim's six-group-and-five-element optical block draws scenes with a noticeably curved focal plane. This means that photos are not uniformly crisp across the frame and that the extreme edges and corners never get sharp. Resolution hits its peak in the f/4-11 range, but the edges are still soft even at those settings. This lens isn't a good choice if you're after technical perfection.

(Credit: Jim Fisher)

But the XSlim completely sidesteps a common problem with pancake M lenses: color shift. Lenses originally designed for film cameras (like the aforementioned Lomo Minitar 32mm) or those with more rudimentary optics (like the Funleader Caplens) typically show false magenta color at the left and right edges of the frame. The color cast is there because, unlike with film, digital sensors work best when light strikes a pixel straight on. Those lenses simply weren't made with that consideration in mind.

I see some barrel distortion (about 2.5%) at test shots near the minimum focus distance. It's a modest effect in the field, but something you might notice for scenes that call for straight lines. I didn't attempt to correct it in sample photos but did play around with some architectural shots in Lightroom and found a +8 adjustment to the manual distortion correction slider compensates for the effect.

(Credit: Jim Fisher)

Vignetting is visible at f/2.8, another easily correctable aspect that, if left alone, contributes to the look of the lens. I don't mind it since the corners are blurry anyway and the effect adds a natural frame to photos. The vignette becomes less apparent starting at f/4, so you can stop down if you don't like it and don't want to correct it in editing.

The curved field of focus affects the character of the bokeh, too. Although the Funleader x Brightin Star is a wide-angle lens, it's still capable of drawing photos with soft backgrounds, especially at closer distances. The defocused highlights are circular with the aperture set wide-open and free of any ugly false texture.

(Credit: Jim Fisher)

The neatest thing about the XSlim's bokeh is its somewhat uneven nature. Typically, everything behind an in-focus subject is uniformly blurry, but the XSlim often shows patches of background that are in clear focus. I spotted it in a few scenes, including in the preceding image where the point of focus is dead-center on the monument and wreaths. The backdrop directly behind the subject is predictably defocused, but a large tree far in the background on the left and a bush behind a row of stones on the right both also manage to be on the plane of focus.

(Credit: Jim Fisher)

I did spot some longitudinal chromatic aberration (LoCA) in a couple of scenes, which manifests as false green color in the bokeh. You can spot it in the snapshot of a friend above—around the top of her head, in the cars parked on the street over her shoulder, and around the windows of the house in the left part of the frame. It's a situational issue for sure and is more evident in backlit and high-key shots. I do not see any purple fringing around power lines or tree branches, which indicates an absence of lateral chromatic aberration.

(Credit: Jim Fisher)

The lens doesn't include a hood and adding one would take away from its ultra-thin design. The front element is pretty small though, so flare isn't a big concern for most photos. If you work against a strong backlight, you can expect some contrast loss and a glowing flare effect. Internal reflections cause some false color if you point the lens directly into the sun or another bright light source, too. At wide apertures, this light tends to spread out into an arc; I managed a ring of fire flare effect at the bottom of the frame when I pointed the lens up to grab some fall leaves. This is another situational effect, but it shows how you can get some dramatic looks from the lens that more mainstream options would miss.

(Credit: Jim Fisher)

I'm not a huge fan of the sunstars from this lens. The 5-blade aperture features rounded blades, which make for less dramatic starbursts with tines that spread out into streaks. The ghosting effect that's relatively soft is more dramatic at the f/11-16 settings you need to use for the effect too; it shows up as a typical circular shape.

(Credit: Jim Fisher)

More Than Just Different

It's refreshing to see a pair of indie camera brands work together to release a lens that's not just another version of what's already on the market. But that's not the sole reason why the Funleader x Brightin Star XSlim-M F2.8 earns our Editors' Choice award. The lens stands on its own as a well-crafted piece of kit with brass construction, reliable rangefinder focus, and a strikingly small design. It also costs much less than equivalent Leica, MS-Optics, or Voigtlander glass at $370. We don't expect its characterful optics to appeal to technicians, but artists who want to create imperfect and unique renderings of their subjects shouldn't hesitate to pick up the XSlim-M.