Sony has introduced two new super-telephoto prime lenses for its E-mount system: the FE 400mm F4.5 GM OSS and the FE 600mm F6.3 GM OSS. These lenses are marketed as the lightest of their kind, with weights of approximately 994g (35oz) and 995g (35oz) respectively. This is a notable improvement over competing models like Nikon's 400mm f/4.5 VR S (1,160g) and 600mm f/6.3 (1,360g). The lenses are targeted at wildlife and sports photographers who often need to carry heavy gear over long distances. They are also lighter than Sony's own high-end 400mm F2.8 GM OSS and 600mm F4 GM OSS lenses, which weigh around 2,895g and 3,040g respectively. The FE 400mm F4.5 GM OSS is priced at £2,400, while the FE 600mm F6.3 GM OSS costs £3,300. Each lens comes with a soft padded case, handle, shoulder strap, and lens hood. Both include Sony's Optical SteadyShot (OSS) stabilization system, which helps reduce camera shake, and are weather-resistant. They also feature a removable tripod collar for easier mounting on tripods. The lenses support Sony's 1.4x and 2x teleconverters, which extend the focal length but reduce the maximum aperture—potentially limiting their effectiveness in low-light situations or for capturing fast-moving subjects. The lenses are equipped with an 11-blade aperture for smooth background blur (bokeh), and use extra-low dispersion elements and Sony's Nano AR Coating II to minimize chromatic aberration, flare, and ghosting. They also include twin XD linear motors for fast and precise autofocus, capable of tracking moving subjects at up to 120fps, which supports 4x slow-motion video. The 400mm lens is recommended for photographing larger wildlife subjects, while the 600mm model is better suited for capturing smaller creatures at a distance. During testing, the lenses performed well in various conditions, including bright daylight, light rain, and fading daylight. Image quality was described as impressive, with sharp details and controlled chromatic aberration. However, occasional softness was noted when photographing large mammals at the maximum aperture. The lenses are positioned as a more affordable option compared to Sony's high-end 400mm and 600mm primes, though they are still considered expensive. As part of Sony's GM (Grand Master) series, they are designed for professional use and are compared to other Sony lenses like the 400-800mm F6.3-8 G OSS and the 100-400mm F4.5 GM OSS, which offer zoom capabilities but at the cost of increased weight and reduced aperture brightness.