The Olympus Zuiko Digital 25mm is known as a ‘pancake’ lens for good reason: measuring 64mm in diameter and just 23.5mm thick, it’s the thinnest lens available in the Four Thirds fit. It’s literally dwarfed by any other Four Thirds lens you put next to it, and to illustrate this difference we’ve pictured it below, alongside the older Zuiko Digital 14-45mm kit lens and the premium 12-60mm zoom. Suffice it to say it’s much lighter too: just 95g to the 190, 285 and 575g of the 14-42mm, 14-45mm and 12-60mm lenses respectively.

The Olympus 25mm pancake is an ideal match for the company’s smaller DSLRs, especially the E-4xx series. Fit the lens on an E-4xx and you’ll have yourself a seriously compact kit which could even squeeze into larger coat pockets.

The 25mm is also a good physical match for the E-5xx series, although looks a little small when mounted on the flagship E-3.

The 25mm belongs to the Standard Olympus lens range, alongside the kit zooms, and is built to a similar quality. It’s obviously a lightweight model with mostly plastic construction, but it feels well-built, with a very smooth manual focusing ring and a metal lens mount.

There’s no focus distance markings which seems understandable given the size of the lens, although it’s worth noting Pentax manages to squeeze them onto its 40mm pancake lens which is actually even thinner at an almost unbelievable 15mm.

Like the Pentax pancake, the lens cap is a screw-on model which at first seems inconvenient compared to a clip-on cap, but before long you can remove and remount it fairly quickly. The filter thread of the Olympus 25mm pancake is 43mm, and the end section doesn’t rotate while focusing. Olympus doesn't supply a lens hood, but the optional LH-43 model will provide a little shielding.

Internally the optical design consists of five elements in four groups with one aspherical element. The maximum and minimum apertures are f2.8 and f22 respectively with a seven-blade system. An f2.8 aperture isn’t unusual for a prime fixed focal length lens, but it does give the 25mm pancake an advantage over most kit zooms.

Olympus 25mm blurred point of light (crop) 25mm at f2.8, focus infinity, point source 1m

Most kit zooms, including the popular Olympus 14-22mm, start at f3.5 when zoomed-out and end at f5.6 when zoomed-in. This means the 25mm pancake is two thirds of a stop brighter when the kit zoom is at wide angle, and two stops brighter when it’s zoomed-in. This brighter aperture gives it an advantage in low light situations, while also allowing a smaller depth-of-field to be achieved – handy for portrait work.

You can’t have everything on a lens of this size and weight though. While the bokeh (out of focus effect) can look fine on normal photos, patterns of concentric rings can be seen on blurred point sources of light like the reflection of the Sun on rippling water.

You can see a cropped example here taken at f2.8, although to be fair we deliberately pursued this effect rather than finding it had occurred in natural use. Coincidentally, a similar effect was noticed when testing the Olympus 14-42mm and 12-60mm lenses.

Olympus Zuiko Digital 25mm focusing

The Olympus Zuiko Digital 25mm takes approximately one second to focus from its closest focusing distance to infinity using the E-420 body, with an audible motorised whir while doing so. Mounted on the flagship E-3 the focusing felt subjectively a fraction quicker and the tone of the motor a little different, but the experience was very similar to using the lens on the E-420.

As such it’s by no means the quickest or quietest lens in the Olympus range, but equally neither cause a problem and in terms of speed and noise, it’s comparable to most kit zooms. You can hear this focusing in action in our video tour.

A quick note on focusing distance. According to the official specifications, the closest focusing distance is 20cm, although we found we could focus slightly closer – typically down to 17cm between the subject and the focal plane.

The 25mm pancake is one of only three lenses in the current Olympus range which supports the contrast-based auto-focusing mode of the E-420 and E-520 bodies. In order to support this ‘Imager AF’ mode, you’ll need to fit either the 25mm pancake, or the 14-42mm or 40-150mm kit zooms.

Like most For Thirds lenses, the 25mm pancake employs motor-assisted manual focusing. As mentioned above, the manual focusing ring is certainly very smooth and also doesn’t rotate while auto-focusing, although like other motor-assisted lenses, the manual focusing experience can feel a little detached.

If you’re new to the Four Thirds system, you may also find it odd not being able to adjust the focus without first powering-up the camera, and also finding some bodies automatically resetting it to infinity when powering down. It’s all a matter of personal preference and getting used to it though, and won’t cause any surprises to anyone familiar with the Four Thirds system.