Review
Sony FE 100 mm f/2.8 STF GM OSS: a lens that does bokeh differently
A 100 mm portrait lens with an apodization element that renders the background more smoothly than ordinary lenses. I explain what STF means, what you pay for it and who it's worth it for.
The Sony FE 100 mm f/2.8 STF GM OSS isn't a lens you buy off a spec sheet. You buy it for how the out-of-focus background looks – and in that respect it has few rivals among E-mount lenses.
STF stands for Smooth Trans Focus. It refers to a special apodization element inside the optical design, not soft focus.
What the apodization element does
The apodization element is essentially a neutral density filter whose density gradually increases from the center to the edges. Light passing through the edge of the lens is attenuated, while the center lets it through with almost no loss.
That's why out-of-focus highlights have no hard edge – their brightness gradually fades toward the rim. The transition between the plane of focus and the background looks smooth, without the rings and double outlines that give away the blur on ordinary lenses.
The price you pay is lost light. The lens has an f/2.8 aperture, but its actual transmission corresponds to T5.6. So for exposure, expect to lose roughly two stops compared with a regular f/2.8 lens, while the depth of field stays the same as at f/2.8. You won't notice it in sunshine, but you will at dusk – either the ISO goes up or the shutter speed gets longer.
What the lens offers besides bokeh
- 100 mm focal length on full frame, meaning a relaxed portrait perspective without facial distortion
- OSS optical stabilization that works together with in-body stabilization
- macro mode via a switching ring: in the 0.57–1.0 m range you get 0.25× magnification
- an aperture ring that can be declicked for smooth operation in video
- 11 aperture blades, 72 mm filter thread, 700 g weight
- dust and moisture sealing
Portraits: where it makes sense
On full frame, 100 mm is a comfortable portrait focal length. For a waist-up portrait you stand far enough away for facial features to stay natural, yet close enough to talk to your model normally.
The apodization element shows most where ordinary lenses struggle: branches against the sky, foliage in the sun, city lights behind the model. Where other optics render distracting rings, here you get a smooth, even wash.
The flip side is autofocus. The lens focuses reliably, but because of its lower transmission it slows down noticeably in poorer light. It's not the first choice for running kids or dancers at an indoor event.
Macro mode in practice
The switching ring changes the focusing range. In the macro position you can focus down to 0.57 m with 0.25× magnification, which is enough for a close-up of a ring, a flower or part of a product.
It isn't true 1:1 macro. On a portrait lens, though, it's a useful bonus that saves you from swapping lenses.
What to watch out for when buying used
- Shine a flashlight through the front and rear elements against a dark background. On a lens with an apodization element, dust and haze in the optics show up in the background rendering sooner than on a conventional design.
- Try both rings – the aperture ring (including the declick switch) and the macro switch. They must move smoothly and without play.
- Turn OSS on and off. With stabilization off, a slight rattle is fine; with it on, it must be quiet.
- Check the mount and the rubber gasket – on a 700 g lens, wear shows up there first.
- The lens hood and front cap are expensive to replace on this model, so factor them into the price.
Who it's for and who it isn't
It makes sense for portrait photographers, wedding photographers with a calmer working style, and video creators who want a cinematic look without post-production.
It doesn't make sense as an all-purpose 100 mm for your bag. For sports, documentary work in low light or travel, a conventional lens with the same aperture and full transmission is more practical.
Conclusion
The Sony FE 100 mm f/2.8 STF GM OSS is a specialized tool that does one thing better than the rest and deliberately gives ground elsewhere. If background rendering is worth two stops of light to you, it's one of the few lenses that will truly change the look of your photos. If you mainly care about a fast aperture, go for a conventional 100 mm or an 85 mm.