A New Kind of 100–400mm: Constant F4.5 and Closing a Long-Standing Gap
Sony’s new FE 100-400mm F4.5 GM OSS lens is more than a refresh; it strategically fills a missing slot in the company’s telephoto lineup. While the 2017 FE 100-400mm F4.5-5.6 GM OSS remains in Sony’s “Enthusiast and Amateur” tier, the new version steps up into a hybrid Professional/Enthusiast category, giving photographers a more capable option without jumping to exotic super-telephoto primes. As a constant aperture zoom, the Sony FE 100-400mm lens maintains F4.5 from 100mm all the way to 400mm, making it up to one stop brighter at the long end than its predecessor and significantly brighter than the FE 200-600mm and FE 400-800mm at equivalent focal lengths. For wildlife and sports photographers, this means more flexibility at dusk, in indoor arenas, or under unpredictable lighting, while still keeping the lens in a mid-range, upgrade-friendly tier rather than an ultra-premium niche.
Why a Constant F4.5 Aperture Matters in Fast-Paced Telephoto Photography
The move to a constant F4.5 maximum aperture fundamentally changes how this telephoto zoom behaves in the field. With the original FE 100-400mm F4.5-5.6 GM, the lens darkened to F5.6 at 400mm, forcing photographers and videographers to adjust ISO or accept slower shutter speeds as they zoomed in. The constant aperture zoom design avoids this exposure shift entirely, keeping brightness consistent throughout the range. For telephoto photography of unpredictable subjects—think birds in flight, sideline action, or photojournalism—this translates to fewer missed frames and simpler workflows in shutter-priority or manual modes. Videographers benefit as well: there is no need for ISO ramping or reliance on auto exposure that can cause visible brightness pumping during a zoom. Essentially, the new FE 100-400mm F4.5 GM OSS behaves more like a cine zoom in terms of exposure stability, but in a stills-oriented form factor.
Internal Zoom Design: Stable Handling for Gimbals, Blinds and Sidelines
One of the most consequential updates is the internal zoom design. Where the original FE 100-400mm extended its barrel significantly as you zoomed, the new lens maintains a fixed physical length across the 100–400mm range. For telephoto specialists, this has immediate benefits: balance on the camera body remains consistent, which is critical on monopods, gimbals, and long shooting days in the field. The lens no longer pumps air in and out as it zooms, reducing the risk of dust ingress when shooting wildlife in dusty plains or coastal environments. In cramped spaces such as press boxes or wildlife blinds, the barrel no longer creeps toward railings or camouflage covers. Sony also adds a zoom smoothness switch with “Smooth” and “Tight” settings, allowing shooters to prioritize quick framing for tracking fast subjects or firmer resistance when maintaining a precise composition is more important than rapid zooming.
Four XD Linear Motors and Fast Autofocus for Action Work
Autofocus performance is central to any telephoto photography lens, and Sony has clearly targeted action shooters with this update. The FE 100-400mm F4.5 GM OSS uses four custom-optimized XD Linear Motors driving a floating focus system, backed by Sony’s latest AF algorithms. According to Sony, this configuration delivers autofocus speeds up to approximately three times faster than the original FE 100-400mm F4.5-5.6 GM when paired with the Alpha 9 III, along with roughly 50% better subject tracking. The lens also supports continuous shooting with AF/AE tracking at up to 120 fps on that body, underscoring its role as a fast autofocus tool for high-speed wildlife and sports work. For photographers upgrading from slower, screw-driven or less responsive zooms, this means more keepers in burst sequences, more reliable eye tracking on animals, and fewer focus misses when subjects rapidly change direction or distance.
Positioning and Value: A Versatile Telephoto for Enthusiasts Going Pro
Beyond specs, the FE 100-400mm F4.5 GM OSS is strategically positioned as a bridge between enthusiast zooms and fully professional super-telephoto solutions. Sony keeps the older FE 100-400mm F4.5-5.6 GM, FE 200-600mm, and FE 400-800mm lenses in an “Enthusiast and Amateur” tier, while the new constant F4.5 model moves up into a hybrid Professional/Enthusiast slot. This mid-range positioning makes the lens especially appealing to photographers looking to move beyond kit telephoto options into serious wildlife, birding, or sports work without committing to ultra-large, ultra-expensive primes. They gain a constant aperture zoom, internal zoom design, advanced optics with ED XA and Super ED elements, and fast autofocus in a single package. In practical terms, the lens offers a blend of reach, speed, and handling that better matches the demands of modern mirrorless bodies, ensuring it will become a go-to tool for many growing telephoto shooters.