Why This 28mm Pancake Belongs on the Smallest Full-Frame Body You Can Buy

The Lumix S9 launched as one of the smallest full-frame mirrorless cameras you can buy, and then sat there without a lens small enough to prove the point. Now a metal pancake the size of a lens cap has arrived in L-mount, and it fills that gap.

Filming from his local park through shifting light and shade, Jimmy Cheng walks through the Viltrox 28mm f/4.5, a lens he first reviewed on the Nikon Z mount and now revisits for L-mount. The optical formula hasn't changed, since this is only a mount difference, so the verdict carries over. What changes is the pairing. Mounted on the Lumix S9, the collapsed lens sits thinner than a kit zoom, turning a full-frame body into something close to pocketable. Cheng frames this as the accessory the S9 was missing at launch, when sales suffered partly because nothing small enough existed to match the body.

The image quality holds up better than the price and category suggest. Cheng calls the center sharpness faultless at f/4.5, the only aperture available, with edges softening a touch but nothing worth complaining about at this level. Distortion is nearly gone, and fringing stays well controlled optically. The surprise is the sun star, which he says is among the most impressive he's seen from a fixed-blade lens when you shoot directly into a bright source. Flare is the weak point, showing low-contrast patches at certain angles. Autofocus is adequate rather than quick, and video shooters will notice heavy focus breathing, so this is a snapshot and stills lens more than a rig lens.

The broader story is what this class of lens has become. For years the "lens cap lens" meant manual focus, a fixed hyperfocal distance, and an aperture stuck at f/8 or f/11, sold cheap and treated as a novelty. This one has a metal build, autofocus, and a relatively bright f/4.5 opening, which puts it a step above the pack while keeping the same disc-thin profile. That shift matters as manufacturers lean into smaller full-frame systems. A 28mm focal length is wide enough for a family selfie and tight enough for a walk through a park or a street, which makes it a natural single-lens setup for a day out. If you own an S9 or any compact L-mount body and want the smallest possible full-frame kit, this is the lens that finally delivers the concept the camera was built around.

Cheng recommends it plainly, arguing every photographer should keep a lens like this in the bag because you never know when compact is exactly what you need. He also notes the sample images speak for themselves, and the review sends you to a run of them to judge the sharpness and rendering yourself. His take on the S9 pairing is the part worth hearing in his own words, since he bought the camera specifically to test L-mount glass and has more of it coming.

Watch the full breakdown above to see the sample gallery and hear how the sun star and autofocus hold up in real use.