Sony FE 100-400mm F5.6-8 OSS Lands at $849, Undercutting the GM by Two Thirds
Sony already sells a 100-400mm. The GM version has been around since 2017, weighs about 1,395g, and still asks roughly $2,500. The new SEL100400 covers the identical focal range at 654g and $849.99, shipping in September. Canada gets it at $1,079.99.
The money came out of the aperture. The GM opens at f/4.5-5.6. This one starts at f/5.6 and closes to f/8 by the long end. That is the whole trade, and whether it matters depends entirely on where you shoot.
What f/8 at 400mm actually costs you
At 400mm you already need a fast shutter for anything with feathers or wheels. Call it 1/1000s minimum for birds in flight. In good open light, f/8 gets you there at ISO 800 or so and modern Sony sensors do not blink at that. Under canopy, at dawn, at an indoor arena, you are suddenly at ISO 6400 and making excuses.
So the honest framing is that this is a daylight lens. Birders working open water and marshland, parents on a sunny touchline, plane spotters, people shooting trains from a hillside. Sony’s own press language says as much, listing birds, sports, trains and aircraft, all of which happen outdoors.
Add the SEL20TC teleconverter and you reach 800mm, or 1,200mm equivalent in APS-C crop. You also land at f/16. Sony bodies will still autofocus down there, but the image circle is doing a lot of work and you should treat that number as a specification, not a plan.
The close-focus number is the sleeper spec
Minimum focus is 0.86m at 400mm and 1.13m wide, with maximum magnification of 0.41x. That is high for the category. Most super-telephoto zooms in this price bracket sit around 0.2x to 0.25x. Nearly half life size at the long end means dragonflies, butterflies and flower heads from a working distance where you do not spook anything.
For a lot of buyers that will end up being the reason to keep the lens. A super-telephoto that doubles as a long-working-distance macro substitute is a genuinely useful thing to have on one body.
Optics and handling
Two ED elements and two aspherical elements, nine-bladed circular aperture, linear motor AF, built in optical stabilisation that coordinates with body IBIS and Active Mode. Breathing compensation is supported for video. There is a focus hold button, a focus mode and range dial, and a zoom lock. Dust and moisture resistant, with the usual asterisk that this is not a guarantee.
Sony quotes up to 120fps with AF and AE tracking on the a9 III. Nobody buying an $850 lens is pairing it with a $6,000 body, but it tells you the AF drive is not the bottleneck.
Where it sits
The obvious comparison is the Sigma 100-400mm DG DN, which is a bit heavier, a bit dearer, and gives you f/6.3 at the long end instead of f/8. Then there is Sony’s own 200-600mm G, which is optically excellent and weighs over 2kg, which is a different lens for a different person.
654g is the real headline. That is roughly the weight of a 70-200mm f/4. It means the lens goes in the bag on the off chance rather than because you planned a wildlife day, and lenses that get carried get used. The GM is better glass. This is the one that will actually be around your neck.