Sony made big claims about its FE 100mm F2.8 STF GM OSS when it was launched earlier this year, particularly about the bokeh it produces. And it's the first lens of its kind to include both autofocus and optical image stabilization. Early on we talked a bit about the principles behind this lens, but we were long overdue for some real-world examples. So when we managed to get a copy in the office, we took it on an engagement, child, street and colleague portrait shoot. Take a look at our sample gallery demonstrating its capabilities both inside the portrait studio and out in the wild.

Pay particular attention - in our aperture progressions - to just how buttery smooth the bokeh is at F2.8 (EXIF indicates the T-stop, so states 'F5.6' - or technically T5.6 - for F2.8). Almost too smooth for some tastes, blurring out-of-focus highlights so much as to lose all character. This lens approaches a very Gaussian blur wide open, rendering out-of-focus highlights more of a blur than defined circles. That's desirable to some as it ensures that background and foreground elements don't distract from the main subject. To others though, it can be too much: for example, I shot the above engagement shot at F8 just to get some circular character to the out-of-focus highlights, rather than a perfectly blurred background.

In other words this lens will be loved or hated. Read on for some of our salient findings.

Like it or not, shoot this lens wide open and you still won't get much flare, thanks to its flare resistance. This was an attempt to induce flare, and yet it's minimal. Photo: Rishi Sanyal

Buttery F2.8 bokeh, with F4 DOF

You can get buttery smooth bokeh, but with the depth-of-field of F4 or more, even wide open at F2.8. That's because the apodization filter cuts out so many peripheral light rays as to effectively make a F4 lens - in terms of depth-of-field - at F2.8, but with the light transmission of F5.6 and the bokeh of F2.8. This is great for video, where you might want multiple subjects in focus due to the F4 equivalent depth-of-field (according to our friends over at Imaging Resource), but with the background blur of F2.8 or faster lenses. The 11-blade circular aperture particularly helps keep bokeh smooth as you stop down.

Autofocus

This is one of the only lenses ever made with such a strong apodization filter that still autofocuses. No doubt this is impressive, but we found AF worked best in good light, with some inaccuracies creeping up as intermittent back or front-focus in challenging light. It's understandable for AF performance to drop in low light given that phase detection depends heavily on peripheral light rays: the exact rays this lens' apodization filter filters out. But we also experienced misfocus in the backlit engagement shots above. Other times, focus was tack sharp even in low light. We'll investigate further but, for now, our experience indicates you may experience some hunting or misfocus outright in challenging light. To be fair though: most competitor lenses are simply manual focus.

Chromatic aberrations

... are noteworthy because they're largely absent. Lateral CA is automatically corrected for (it's mandated in ACR), and axial CA (the bad kind) that shows up as hard-to-correct green or purple fringing behind or in front of the focal plane, respectively, is largely absent. If you really pixel peep the image below, you can see some slight cyan fringing, but it's hardly noticeable or offensive.

In bright light, this lens nails focus, wide open even with Eye AF. And it's tack sharp at F2.8 (T5.6). Axial chromatic aberration, which manifests as green and purple fringing, is well-controlled, evident from its absence in this photo. Photo: Wenmei Hill

Best in bright light

This is not an ideal lens for low light. You start with T5.6 (at F2.8) b/c of the incredibly strong apodization filter that blocks out most peripheral light rays. By the time you stop down to get any circular, defined character to your highlights (as opposed to almost too buttery-smooth Gaussian bokeh), you suddenly find yourself at T8.0 or worse. That's a huge light cost, so don't expect to be using this lens in dimmer situations, when the lens starts hunting or missing focus anyway.

Tack sharp

This lens is sharp. Pull up the loupe on the wide open, F2.8 (T5.6) child portrait above or check out this model in Thailand: the eyes of our subjects are unbelievably sharp for a 42MP sensor.

Too smooth?

A number of photographers - ourselves included - have been struggling with the following question: is the bokeh too smooth? Take a look in the rollover below at the effect of stopping down a mere 1/3 EV T-stop (the smallest discrete step you can take), paying particular attention to the bright out-of-focus lights behind the flower:

F2.8 (T5.6) T6.3

Out of focus highlights behind the flower go from an indiscernible blob to circular out-of-focus highlights. The drastic transition despite a mere 1/3 EV difference speaks to just how dark the outer portion of the apodization filter is: as you stop down its effect become (immediately) less severe, F-stop and T-stop converge, and out-of-focus highlights start to become more defined again (which means bokeh starts looking more traditional).

Many prefer the more traditional bokeh as you stop down: the former, almost too Gaussian, blur wide open leads to a character not immediately appreciated by all. For example, the vertical portrait of our model above almost looks like a cut-out of her against the blurred background. On the other hand, the background's lack of character means it isn't distracting, allowing you to focus on the main subject, with the added advantage of more depth-of-field for couples portraits like our leading image at the top of this story. You win some, you lose some.

Take-home: should I buy this lens?

Whether or not you like this lens will be a highly personal, subjective decision. On the one hand, the lack of discernible out-of-focus circles when it comes to your point light sources means that all background and foreground out-of-focus elements meld together into a smoothly blurred, undistracting surrounding, with no harshly interfering edges. On the other hand, you get backgrounds and foregrounds lacking the character I see in a traditional lens image below:

Not taken with the Sony 100mm F2.8 STF but, instead, with the Nikon 70-200 F2.8E FL ED VR on a Nikon D5. I personally prefer my out-of-focus highlights to be defined circles or ellipses. On the other hand, for those finding these 'artifacts' distracting, the Sony 100mm F2.8 STF will render these so smooth as to not distract you from the main subject matter here: the love story behind the bokeh. Photo: Rishi Sanyal

It's up to you to decide what you prefer. A few things are certain: this lens is sharp wide open, OSS means you can hand-hold it at reasonable shutter speeds, and your subject will be isolated with very little distracting foreground or background. You'll even get more forgiving depth-of-focus to ensure more of your subject(s) remain sharp, while maintaining smooth bokeh. That's no small feat, and could be incredibly useful: videographers and portrait shooters wanting the entire face, or both members of a couple, in focus while blurring out all distracting foregrounds and backgrounds will appreciate this. But whether or not you like the character of the defocused regions will be highly subjective. Expect some autofocus struggles in challenging light as well. Click the link below to view our results.

See our Sony FE 100mm F2.8 STF
sample gallery

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