Sony announced the FE 100-400mm F5.6-8 OSS on August 4th. It ships in September, pre-orders are open now, and at an announced $849.99 it is the cheapest and lightest way anyone has ever offered to get to 400mm on full-frame E-mount. For a site that spends most of its time answering “how do I get more reach without spending four figures,” this is squarely our beat.
Nearly every writeup has led with the same two numbers: $850 and 654 grams. Both are genuinely impressive. But the number that will actually determine whether you’re happy with this lens is one almost nobody put in a headline.
It’s 220. As in millimeters. That’s where the lens reaches f/8.
Why 220mm is the number that matters
A lens badged “F5.6-8” sounds like it gives you f/5.6 for a decent chunk of its range and only gets dim at the very long end. That’s how variable-aperture zooms are usually read, and it’s how this one will be read by a lot of people clicking pre-order this week.
Per PetaPixel’s coverage of the announcement, this lens is at f/8 by 220mm. Fstoppers, testing a review sample, puts the f/5.6 window as ending around 205mm and draws the obvious conclusion: wildlife work at 200 to 400mm is effectively an f/8 lens.
Now ask yourself the honest question. When you put a 100-400 on the camera to photograph birds, where is the zoom ring? It is at 400mm. It lives at 400mm. You bought a 100-400 for the 400, and the 100 end is there so the lens can exist as a zoom. Roughly the top half of the range, which is the only half most wildlife shooters use in anger, is f/8.
So this is not an f/5.6-8 lens in practice. It’s an f/8 lens with a bright end you’ll rarely visit. That’s not a scandal, and it’s not hidden – it’s right there in the name. But it reframes the buying decision, because you should be comparing it against other lenses at f/8, not at f/5.6.
What one stop actually costs
f/5.6 to f/8 is exactly one stop. One stop sounds academic until you put it where wildlife photography actually happens, which is the first and last ninety minutes of daylight.
Fstoppers’ reviewer gives the concrete version. Shooting in low-light woodland, they were pinned between ISO 6,400 and 12,800 at shutter speeds of 1/320 to 1/400 second. Sit with both halves of that sentence. ISO 12,800 is a lot of noise to hand a small, distant subject. And 1/320 second is slow for a bird – it’s a shutter speed that produces sharp perched subjects and soft ones the moment anything moves.
That reviewer also names the compounding problem precisely: high ISO noise overwhelms fine detail exactly when your subject is smallest in the frame. This is the trap. The situations where you most need to crop hard are the same situations where you’re deepest into the ISO range, and cropping magnifies noise while shrinking the detail you’re trying to keep.
Against the obvious rivals, the gap is narrower than the marketing suggests but it runs the wrong way. Sigma’s 100-400mm F5-6.3 and Tamron’s 50-400mm F4.5-6.3 are both f/6.3 at the long end, which is two-thirds of a stop brighter than f/8. Not transformative. But two-thirds of a stop is the difference between ISO 6,400 and ISO 10,000, and on a heavily cropped frame you will see it.
The f/8 autofocus worry is mostly obsolete
Here’s where a lot of the internet is about to give you outdated advice, so it’s worth being clear.
Photographers who came up on DSLRs learned a hard rule: phase-detect autofocus dies at f/8. It was true, it was a real constraint of dedicated AF sensors sitting under a mirror, and it shaped a generation of buying advice about teleconverters. That rule does not transfer cleanly to modern on-sensor phase detection.
The evidence from this specific lens is encouraging. Fstoppers reported autofocus that impressed in continuous mode and stayed quick even with a 2x teleconverter attached – which puts the effective aperture at f/16, far past the old DSLR wall. On gulls in flight, they measured it outpacing two comparison lenses by a tenth of a second.
So no, f/8 is not going to stop your camera from focusing. What it will do is subtler and still worth planning around: the same reviewer noted the hit rate dipped noticeably in dim light. Autofocus systems see through the lens at its maximum aperture, and a dimmer, noisier live feed gives subject-detection algorithms less to work with. You won’t lose focus. You’ll lose some percentage of a fast sequence, on the frames you most wanted, in exactly the light where you’re already struggling.
What the reviews say about sharpness
Reasonable for the class, with an honest ceiling. Fstoppers found the 100mm end very good in the centre and excellent stopped down to f/8. At 400mm – again, where you’ll live – centre sharpness holds up reasonably well, contrast improves noticeably by f/11, and it never turns razor sharp. Corners stay softer, with some blue fringing that doesn’t fully clear up.
Note the awkward implication of “contrast improves at f/11.” Your optical sweet spot at 400mm is a further stop down from an aperture that is already costing you ISO. In good light that’s a free improvement. At dusk it’s a choice you won’t get to make.
Sony has been upfront that this is a consumer-grade zoom and won’t deliver the resolution, image quality, or bokeh of its G and G Master lenses. That’s a refreshingly honest position for a manufacturer, and it’s the correct frame for the whole lens.
The case for it, which is stronger than it sounds
Everything above is the cost side. Here’s the other half, and it’s genuinely compelling.
654 grams. DPReview points out that’s roughly half the weight of the Tamron 50-400mm or the Sigma 100-400mm. Retracted it’s about 165mm long and takes 67mm filters – the same thread as a lot of ordinary kit, not the 82mm-and-up specialist glass you’d otherwise be shopping for.
This matters more than spec-sheet arguments usually allow. A telephoto you leave in the car because it’s heavy has an effective aperture of zero. Half the weight means it goes in the daypack on a hike where the Sigma stays home, it handholds comfortably for an afternoon instead of forty minutes, and it doesn’t demand a monopod to be usable. If you’re a hiker who photographs wildlife rather than a wildlife photographer who hikes, that trade is not close.
It’s also more capable at close range than the reach spec suggests: 0.41x maximum magnification with a minimum focus distance of 1.13m at the wide end and 0.86m at telephoto. That’s within a nose of half life-size. Dragonflies, butterflies, frogs at the pond edge – this is a genuinely useful near-macro tool, and near-macro subjects tend to sit in better light than forest birds do.
So should you pre-order?
A clean decision rule, based on what’s been published so far.
Yes, if you shoot in open habitat – shorelines, marshes, meadows, raptors against sky – where light is plentiful and f/8 costs you nothing you’ll notice. Yes if weight is the reason your current telephoto doesn’t get carried. Yes if you’re getting into wildlife and want to find out whether 400mm is enough for you before committing to glass that costs three times as much.
Look elsewhere if your subjects are forest birds, understory mammals, or anything at dawn and dusk under canopy. That’s the exact scenario where f/8 hurts most, and where two-thirds of a stop from the Sigma or Tamron, or the extra reach of Sony’s 200-600mm, will do more for your keeper rate than saving weight will.
Check your body before you check the lens. This is the part that gets skipped. Once you accept an f/8 lens, your camera’s high-ISO performance stops being a nice-to-have and becomes the actual limiting factor in your system. Pairing this with a recent full-frame body that stays clean at ISO 6,400 is a coherent plan. Pairing it with an older or APS-C body is a decision that deserves thought – the crop gives you a 600mm equivalent field of view (if you’re committed to APS-C, the Sony E 70-350mm G OSS is the lighter, cheaper way to similar reach), which is tempting, but it takes away high-ISO headroom at precisely the moment the lens is asking for more of it.
The honest summary
Sony built the lens a lot of people have been asking for: light, affordable, and long, with the compromise placed on aperture rather than on reach, weight, or price. That’s a defensible set of choices, and for daylight shooting in open country it’s close to the obvious pick.
Just buy it knowing what it is. The badge says F5.6-8. From 220mm onward – the entire range you bought it for – it’s an f/8 lens, and everything downstream of that, your ISO, your shutter speed, your autofocus hit rate in the gloom, and how hard you can crop, follows from that one number.
Reviews so far are based on pre-production and early samples. It ships in September. If you shoot the difficult light, there’s no penalty for waiting for the first full production reviews before committing.
The shortlist
Everything discussed above, in one place:
- Sony FE 100-400mm F5.6-8 OSS – the lens in question. Lightest and cheapest route to 400mm on full-frame E-mount. Ships September.
- Sigma 100-400mm F5-6.3 DG DN Contemporary – two-thirds of a stop brighter at the long end, roughly double the weight.
- Tamron 50-400mm F4.5-6.3 Di III VC VXD – the widest range of the three, brightest at the short end.
- Sony FE 200-600mm G OSS – if reach rather than weight is your actual constraint, this is the honest answer.
- Sony E 70-350mm G OSS – the APS-C alternative: 525mm equivalent, far lighter, far cheaper.
- A carbon monopod and fluid head – the cheapest stop of stabilisation you can buy, and it applies to every lens above.
Nature Photo Gear is a participant in the Amazon Services LLC Associates Program. If you buy through the links above we earn a commission at no extra cost to you. We have not handled this lens; every performance claim in this article is attributed to a published review or to Sony’s announcement.
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