Panasonic LEICA DG VARIO-ELMAR 100-400mm f/4.0-6.3 II ASPH. POWER O.I.S. (H-RSA100400)

This Panasonic zoom gives Micro Four Thirds photographers long reach for wildlife, birds and outdoor sport. Distant animals and athletes fill the frame at the 400mm end, and the zoom range gives flexible framing in the field.

The main trade-off is light. The maximum aperture falls from f/4 at 100mm to f/6.3 at 400mm. Panasonic answers with stabilisation and weather sealing rather than a brighter aperture.

Panasonic released this second-generation lens in 2023. The Micro Four Thirds mount fits bodies from several makers.

The lens weighs 2 lb 2.7 oz (985 g) and measures 6.75 in (171.5 mm) long by 3.27 in (83 mm) wide. That weight and size keep the lens manageable on long walks. A screw-in filter must match the 72mm front thread, so you can fit a protective or polarising filter for outdoor work.

Reach is the reason to buy this lens. At 100mm you can hold a bird and its branch in one composition. At 400mm a wary animal fills the frame from a safe distance. The 100mm end also helps when a subject comes nearer than expected.

Light is the constraint. The maximum aperture runs from f/4 to f/6.3 as you zoom, so at 400mm you need bright conditions or a raised ISO. Early morning and dusk, when animals move most, are the hardest hours. A monopod steadies the camera when shutter speeds drop. The smaller aperture also gives less subject separation than a brighter lens would.

Nine aperture blades help keep out-of-focus highlights smooth behind the subject.

Close work is covered too. The lens focuses as near as 4.3 ft (130 cm). It can also reach 0.25x magnification. A butterfly, a flower head or a perched bird can occupy a large share of the frame without any accessories.

POWER O.I.S. helps steady handheld frames at the 400mm end, where every small movement shows. From a hide or a car window, it lets you shoot at slower shutter speeds than the focal length alone would allow. It steadies the camera, not a moving subject, so fast action still needs a fast shutter.

The zoom lock stops the barrel from creeping downward when you carry the lens or point it at the ground. Weather sealing lets you keep working through dust and drizzle on coastal paths or dry game tracks.

There is no fluorine coating on the glass, so the front element needs careful wiping after sea spray or fingerprints.

The lens holds 20 elements in 13 groups. One aspherical element helps correct distortion and spherical aberration, faults that bend straight edges or soften detail. Three low-dispersion elements and one super-low-dispersion element help reduce chromatic aberration. That is the coloured fringing you see along high-contrast edges such as a bird against a bright sky.

Focusing is internal, so the lens keeps its length while it focuses.