The Sony FE 100-400mm f/4.5-5.6 GM OSS has been a staple of wildlife and action shooting for years, but Sony just rebuilt the concept from scratch. The new version brings a constant f/4.5 aperture to a zoom range that has never had one before, and that single change reshapes how the lens competes against the rest of Sony's telephoto lineup.
Coming to you from Jan Wegener, this detailed field review puts the new Sony FE 100-400mm f/4.5 GM through real-world shooting across fast action, low light, and side-by-side comparisons with the Sony FE 200-600mm f/5.6-6.3 G OSS and the Sony FE 400-800mm f/6.3-8 G OSS. Wegener, who has spent over 20 years shooting birds professionally, brings a practical eye to the test rather than a spec-sheet one. At 1.84 kg (around 4 pounds), the lens isn't light, but Wegener found no issues handholding it for extended periods in the field. The internal zoom design and oversized zoom ring make moving through the range fast, though there's a handling quirk worth knowing: in smooth mode, pointing the lens downward causes it to zoom out to 100mm on its own.
Wide open and without a teleconverter, the lens is sharp, contrasty, and consistent across subjects ranging from small bush birds to pelicans to tight portraits. Wegener notes the out-of-focus rendering has a prime-like quality, with smoother, more refined backgrounds than the old Sony FE 100-400mm f/4.5-5.6 GM OSS, particularly when bright highlights appear in a busy scene. In overcast conditions shooting kites and eagles at the beach, the f/4.5 aperture let him hold a shutter speed of 1/4,000 sec or faster while keeping ISO manageable. That's a real advantage over slower lenses at this range, and it's especially apparent when the light drops and the action doesn't.
The teleconverter results are where the review gets genuinely complicated. With the Sony FE 1.4x Teleconverter attached, performance remains strong and autofocus stays reliable at f/6.3 throughout the range. The 200-600mm has a slight edge in raw sharpness at that focal length, but the new lens answers with better background rendering. Add the Sony FE 2x Teleconverter and you're at f/9, which introduces a more noticeable sharpness drop and limits when and where the combination is practical. Against the 400-800mm at 800mm, Wegener found the 400-800mm slightly sharper, though the new lens holds better contrast and color. Whether the tradeoffs make sense depends entirely on what you're replacing and what you're gaining.
Wegener also lays out specific lens replacement scenarios, discusses where he sees this lens fitting into a working kit alongside the 400-800mm, and gives his honest take on the 300mm comparison, which is the toughest call in the whole review. Check out the video above for the full breakdown from Wegener.
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