A Look At The New Sony FE 100mm f/2.8 STF GM OSS With Smooth Trans Focus
The new Sony FE 100mm f/2.8 STF GM OSS lens is one of Sony’s latest lens offerings for their full frame mirrorless cameras. It’s another lens in Sony’s pro-grade G Master series, with built-in stabilization and SSM autofocus system. It’s designed to be used as a portrait lens, and it has what Sony calls a Smooth Trans Focus system.
So what is this Smooth Trans Focus that Sony has been talking about, and is it just a gimmick? Well, for the former, it’s essentially an apodization filter that works together with the 11 blade rounded diaphragm to produce very smooth bokeh with soft-edged out of focus highlights. So what’s an apodization filter? Good question. In the case of this Sony lens, it’s a concave neutral gray tinted lens element near the aperture that produces a smooth transition to zero intensity out on the edge of the frame. In short, think of it as a radial neutral density filter that’s clear in the center, and darker on the edges – the opposite of a conventional center filter that helps combat vignetting. And like vignetting, the apodization filter will get darker as it gets closer to the edge.
Since this filter is limiting the amount of light coming through the lens, this apodization filter cuts up to two stops of light – much like an ND filter would. So while the lens itself is titled as a f/2.8 lens, the markings on the barrel actually start at f/5.6. For clarity, you will still get the depth of field qualities of a 100mm f/2.8; you’ll actually have to meter the exposure value at f/5.6 to ensure the correct exposure.
So why would you want this strange filter in your lens? Well, the results are that it gives you incredible smooth transitions within your bokeh, by knocking out all of the distracting hard edges in the background. It does this by having the out of focus elements create disks instead of your standard points on the sensor plane because they’re out of focus. The filter helps taper off the exposure of those disks, fading them out on the edges. The result is silky smooth bokeh, instead of having distracting elements that you might typically find within bokeh.
Simply, what this lens is: a portrait lens that gives very smooth, natural-looking bokeh.
What this lens isn’t: a lens ideal for low light shooting, or for getting swirly, cat eye, or soap bubble type bokeh
So what does this smooth bokeh look like? Here’s a sample we set up in the studio:
This was at maximum aperture, with the focus on the center of the orchid on the left. The beads hanging in the background just kind of fade to mush. We also did some comparison shots with the Canon 100mm f/2, Zeiss Milvus 100mm f/2 Macro, and Nikon 105mm f/2. DC:
These were all wide open, so they’re a stop faster, but we shot them like that to maximize the bokeh effect to illustrate the difference to the Sony. As you can see, all three of these lenses have hard edges to the out of focus highlights. And that’s the difference.
Just for fun, we also shot test charts with these four lenses, for a quick resolution comparison.
These are single samples that all passed our standard inspection, so don’t put too much weight on these charts. That said, the chart shots show some things we already know, that the Zeiss is nice, the Canon is pretty good, and the Nikon is an old design, and it shows. And the new Sony FE 100mm f/2.8 STF GM OSS looks really good. $1500 good? Maybe, just maybe. If you shoot tons of portrait work, it could certainly be an asset in your bag. If you don’t, it could be a fun weekend rental to try something new.
Side note about the Nikon 105 DC: the defocus control doesn’t soften the edges of the bokeh like an apodization filter. It alters the bokeh by shifting some internal elements forward or backward. The images below show what that looks like in practice.
So what do you think? Do you think this unique design has a future in the photography world?
Author: Joey Miller
I’m Joey. I love cameras, especially old film cameras, and I can’t remember the last day I didn’t take a photo. Digital cameras are great, and they keep me employed, but I also still like processing my own film. I’m stuck somewhere in the middle. I shoot every single day, no matter what.