Why This Lens Deserves Your Attention
The Sony 100-400mm f/4.5-5.6 GM OSS II is probably the most practical telephoto zoom you can mount on a full-frame E-mount body if you shoot anything beyond portraiture. Wildlife, sports, birding, landscape detail work — it covers all of it without requiring you to carry two or three fixed lenses. The first version had reputation issues. The Mark II fixed most of them. Here is how I actually use this lens in the field, not the brochure version. At 400mm on full-frame, even a slight camera shake ruins the shot. The lens has Sony's Optical SteadyShot, which helps, but it is not magic. I usually shoot handheld up to about 1/500s when tracking birds in flight, and drop to 1/1000s or faster if the light allows. The newer AF system with real-time tracking locks onto eyes reliably, but it will still hunt in low contrast situations. I learned this the hard way on a overcast morning at the coast.
My workaround was simple: switch to AF-C with the tracking sensitivity set to +1 or +2 instead of the default. It makes the focus point stick slightly longer before abandoning a subject that momentarily loses contrast. Combined with the back-button focus method, this gives me consistent results without relying on the shutter half-press.
Handling Vibration and Stability
At the long end, lens shake becomes obvious even when you think you are steady. I recommend a monopod if you spend more than twenty minutes tracking moving subjects. The tripod collar on the Mark II is solid, but it rotates around the lens rather than pivoting at the mounting point, which means you need to loosen the plate slightly to tilt. It works once you get used to it. When shooting from a vehicle or boat, the vibration patterns change completely. I usually enable the OSS switch marked as Mode 2 for panning subjects, which stabilizes only in the axis perpendicular to your movement. If you leave it on Mode 1 while panning, the image will drift inside the frame in a way that feels wrong even before you review the photos.
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Focusing Performance Across Distances
The AF speed is noticeably faster than the original version, but it is not instantaneous at close range. When you are under two meters and the subject moves erratically, the lens can overshoot and correct. I set the AF limit switch to the 2m to infinity range when shooting birds at distance, and keep it unset for closer work. This small adjustment usually cuts focus acquisition time by about a third in practical conditions. Another thing that is not mentioned in reviews: the focus breathing is moderate but present. If you are filming video with this lens, the framing shifts slightly when you rack focus from near to far. I compensate by using manual focus peaking and setting the focus distance beforehand rather than riding the AF ring during a take.
Image Quality Expectations
Center sharpness is excellent wide open at f/5.6. Corners improve noticeably when you stop down to f/8, and they are very good at f/11. Beyond f/11, diffraction starts to soften the image on high-resolution bodies like the A7R series. I rarely go past f/11 unless I need maximum depth of field for landscape telephoto work. Chromatic aberration is well controlled, but purple fringing appears in high contrast edges when shooting into the sun. I usually disable lens corrections in-camera and process with the Sony lens profile in post, which removes the fringing without affecting sharpness. The difference is subtle but consistent across my workflow.
Weather Sealing and Durability
The gaskets and sealed construction handle rain reasonably well. I have shot in steady drizzle for an hour without issues, but submerging the lens or pointing it directly into heavy rain is not advisable. The front element protrudes slightly when extended, which means rain droplets collect there more easily. I wipe it frequently with a microfiber cloth rather than letting it air dry. The zoom ring tension is firm and consistent, which prevents accidental focal length changes when the lens is hanging from a strap. The focus ring has a smooth resistance that works well for manual adjustments. Neither ring feels loose after six months of regular use, which is more than I can say about some competitor lenses.
Compatibility Notes
This lens works with all E-mount bodies, including APS-C cameras where the effective focal length becomes roughly 150-600mm. The autofocus speed is slightly slower on older bodies like the A7II due to their contrast-detect hybrid system. On the A9 series and newer bodies with phase-detect AF, performance is as good as the lens is capable of. If you are using the 1.4x or 2x teleconverters, the Mark II handles them better than the original. Image quality degrades predictably, but autofocus remains reliable even at f/8 or f/11 effective aperture. I usually avoid the 2x converter in low light because the viewfinder darkens significantly and AF acquisition slows down noticeably.
What This Lens Does Not Do Well
It is not a fast lens. At f/5.6 at 400mm, you need good light or a higher ISO. Indoor sports or dimly lit arenas will push your ISO well above 3200 on most bodies. If that is your primary use case, consider a faster prime like the 400mm f/2.8 or the 600mm f/4 instead. The lens is also relatively long when fully extended. It does not fit in most standard camera bag compartments without removing it from the body. I carry a dedicated telephoto bag or use the neck strap attached to the tripod collar for quick access.
My Practical Recommendations
Buy the Mark II if you can. The autofocus improvements alone justify the upgrade, especially if you shoot moving subjects regularly. The Mark I is still capable, but the hunting behavior in tricky lighting is frustrating. Spend ten minutes customizing your AF settings before your first serious shoot. The default configuration works, but tweaking tracking sensitivity and AF subject shift settings based on your typical shooting environment makes a real difference. I spent three sessions experimenting with these parameters, and settled on a setup that takes about a week to fully adapt to. Use a UV filter only if you shoot near the coast or in sandy environments. In normal conditions, it adds an extra glass element that can introduce flare and reduce contrast slightly. I stopped using one after noticing haze in backlit shots that disappeared when I removed the filter.
