The Panasonic Leica DG Vario-Summilux 25-50mm F1.7 ASPH is Panasonic’s latest lens for the Micro Four Thirds system.
It covers a slightly unusual 50-100mm equivalent range and maintains an F1.7 maximum aperture throughout. But it makes immediate sense once set alongside Panasonic’s video-optimized 10-25mm F1.7, to which it makes a natural companion.
If the 10-25mm could be seen as a set of wide to normal primes, slotted into a single lens barrel, the 25-50mm lets you extend this set to include 50mm, 85mm and 100mm equivalents.
Despite its relatively modest zoom range, the 25-50mm F1.7 is a complex lens, featuring 16 elements in 11 groups. This includes one aspherical element, three extra-low dispersion (ED) elements and a single ultra-high refractive index (UHR) element. It has 9 rounded aperture blades to give circular bokeh (in the middle of the frame, at least).
The minimum focus distance ranges from 28cm (11″) at the wider end to 31cm (12.2″) at the 50mm setting. This provides it with a maximum magnification of 0.21x (0.42x in full-frame terms).
It’s a fairly large lens, as you might expect of an F1.7 constant-aperture zoom, but it’s not overly heavy, so it handles well on cameras that have a decently sized hand grip.
The detail that isn’t necessarily apparent from the bare specs is that the 25-50’s dimensions are an exact match for those of the 10-25mm F1.7. It’s the same 127.6mm long and 87.6mm in diameter, and its geared zoom, focus and aperture rings share their sizes and spacing with those on the existing lens.
This commonality means that the 25-50mm can be swapped onto a video camera rigged-up with a follow-focus to mesh with the gearing of the 10-25mm. At 654g (23oz) the 25-50mm is a surprisingly lightweight lens, given all the elements inside. This makes it 32g (1.3oz) lighter than the 10-25mm, but neither lens feels especially front- or back-heavy, so we doubt this discrepancy will be enough to throw off the balance of most gimbals.
All three rings on the 25-50mm feature a fine geared texture to them, allowing comfortable fingertip operation while also leaving open the option to use them with geared or motorized accessories.
This and the smoothly rotating aperture ring suggest Panasonic is primarily thinking about video with this lens. That said, while the smooth rotation allows near-stepless control over the aperture, the ring’s large degree of rotation means it’s easy to set the aperture value by hand without the risk of a small nudge knocking it to a significantly different f-number. Clicking the aperture ring over to ‘A’ either provides automatic control of aperture or passes aperture control off to a command dial on a camera body.
Panasonic describes the motor driving the aperture as a ‘micro-step’ drive, and the opening and closing of the aperture doesn’t make the step changes visible.
Like the 10-25mm F1.7, the 25-50mm has a focus clutch mechanism. When you pull the focus ring back, a marked distance scale is revealed. This engages manual focus and also switches the ring’s behavior from being speed-sensitive to offering a linear response (turning to a specific point always puts the focus at a specific distance).
Like nearly all autofocus lenses for mirrorless cameras, the 25-50mm lens is fully focus-by-wire, even when the focus ring is in its manual/linear position, but it behaves exactly as you would expect a mechanically-coupled lens to work, so it should present few surprises in this respect.
However, while the lens exhibits very little breathing as you refocus, it’s not a parfocal design. This means that while you can refocus without significantly changing the framing of your shot, zooming in or out will require you to refocus the lens.
Although a lot of attention has been given to the lens’ manual focus behavior, it is still an autofocus lens. Linear actuators provide fast, essentially silent focus, and are designed to make full use of Panasonic’s latest 240 fps drive (where the focus operation can be adjusted up to 240 times per second).
The 25-50mm F1.7 comes with a fairly deep tube-style hood, which features a button-release catch to ensure it stays in place when you’re using it. The lens also comes with a soft, lightly padded lens bag.
A small rubber gasket around the base of the lens helps makes clear that its design is environmentally sealed, meaning it should pair nicely with the likes of Panasonic’s G9 and the GH-series cameras, which are similarly rugged.
As a photographic lens, a 50-100mm lens might seem a little odd: It doesn’t reach as far as the 70-200mm you might be familiar with, nor as wide as a 24-70mm (or even an old-school 35-70mm, for that matter). The constant F1.7 maximum aperture means you essentially have a set of 50-100mm fast primes for portraiture, for instance, but it doesn’t really offer much in the way of flexibility. The absence of image stabilization means you don’t get the ‘Dual IS’ performance boost from combining in-lens and in-body stabilization.
Where the 25-50mm really starts to make sense is for video, and specifically for videographers who want to be able to shoot something longer than their 10-25mm F1.7, while maintaining a familiar shooting experience. In that regard the continuously variable aperture ring, knurled grip surfaces and well-controlled focus breathing make a lot of sense. It’s hard to imagine it being used on its own, but as a way to extend the 10-25mm F1.7 experience over an even broader range of focal lengths, it seems obvious.