Sony 100mm f2.8 STF GM Review

Specifications

Aperture
Maximum: f/2.8
Minimum: f/20
Size
85.2 x 118.1 mm
Filter Thread
72 mm
Weight
700 g
Max Magnification
0.25
Min Focusing Distance
57 cm
Number of aperture blades
11, Rounded
Elements/Groups
14 / 10
Optical Stabilization
Yes
Weather Resistance
Yes

The Sony 100mm STF lens is perhaps the most unique and controversial lens in the Sony E-mount lineup. When it was first announced, we investigated the lens with great interest, but the 2 stops of light loss and T5.6 transmission instead of true f2.8 led us to believe we wouldn’t be able to make good use of it. Yet as time went on, and we saw more results from the lens, our desire for it grew and grew until we decided to get one for ourselves.

Build Quality

The lens features dust and moisture sealing. Because it is branded a G Master or GM lens, it has a solid construction that feels a bit more premium than the G branded lenses. The lens hood is plastic, while the zoom and focus rings are sturdy and rubberized.

The lens is not too large and heavy, and it feels well-balanced on our Sony a7RIII and a9 cameras. The lens has optical image stabilization (OSS), which is important for getting sharp images at telephoto focal lengths.

With all of the switches on the lens body, it looks quite serious.

[Taken with the Zeiss Batis 85mm]

There are physical controls for focus limiter, AF/MF, optical stabilization, and a focus hold button. The focus limiter ring allows selecting between two focusing ranges: a dedicated close-up range for working with close objects in the range of 0.57m–1.0m with a 0.25x maximum magnification, and farther range of 0.85m to infinity with maximum of 0.14x magnification. The focus hold button can be set to a variety of other functions; we like to set the button to eye autofocus.

The manual aperture ring can be de-clicked for smooth, silent aperture for video purposes. There is some slight focus breathing, but minimal enough that it shouldn’t be too distracting in video.

Finally, the 100mm STF lens has a special apodization filter inside, a lens element that becomes progressively darker towards its edges, causing a few stops of light loss. It is also this filter that causes the extremely smooth blurring effect of a Smooth Trans Focus or STF lens.

[Sony official press material—comparison between STF and traditional lens rendering]

Autofocus

All of the other STF lenses on the market today are manual focus or contrast detect-only, since the apodization filter blocks out the peripheral light necessary for traditional autofocus mechanisms to function.

The T5.6 light transmission of the lens limits its usage in low light conditions without supplemental lighting, but with good high ISO performance on the latest generation of full-frame sensors and Sony’s on-sensor PDAF, autofocus works well even indoors.

In normal lighting conditions, autofocus is fast and smooth, and the silent focusing motor is good for video.

Image Quality

The 100mm STF is likely the sharpest lens we’ve ever used. Independent tests back up our observations, as it is one of the top 3 sharpest lenses in the Sony E-mount system. Stopped down it can serve as a great landscape lens.

While the in-focus areas are extremely sharp, the out-of-focus background blur is extremely smooth. The combined effect is quite entrancing to see, especially at high resolution.

Images feels three-dimensional and realistic, because the smooth transition from in-focus to out-of-focus more closely resembles the way our eyes see the world.

This lens is amazing for flower and foliage shots, especially in the close focusing mode. We’ve seen effects online in other photos, but to effortlessly reproduce it ourselves is a ton of fun. And that’s what a photography hobby should be, right?

For portraits at medium distance, it tames the background but still lets you see what the background is. There are times when this is desirable, but other times when perhaps blowing the background out completely might be preferable. For the most part, we love the way the 100mm STF lens renders.

When the subject is close, there is a very cinematic feel to the resulting image.

The colors straight out of the lens tend towards the neutral cool side compared to the Zeiss Batis 85mm, which tends towards warmer colors. We post-process all of our photos so that this difference is not a major factor.

Indoors, even at around ISO 8000, it still performs very well when paired with full-frame sensors. Unless it’s truly dim light, the lens works well.

[Shot at ISO 16000]

The lens performs well in most situations. Only under extreme backlit conditions will the lens flare and lose some contrast.

For in-focus areas there is no noticeable amount of chromatic aberration or purple fringing even in extremely high contrast situations. For out-of-focus areas, the following illustrates one of the only instances of noticeable CA we have found in our shooting, cropped nearly to 100% to illustrate the effect:

Specular highlights are perfectly round and are smooth in the middle, but can have some more defined edges.

When we compare the rendering of the background blur with our Zeiss Batis 85mm, the difference of the STF lens becomes more apparent. Both are excellent lenses for portraits, but they render the background differently, especially if the scene is busy with foliage or has highlights.

100mm STF — Batis 85mm

Click on the photos to see the larger size. The photos were taken from similar positions, and the 85mm has a wider view of the scene compared to 100mm. The Batis 85mm has more “cat’s eye bokeh balls,” and the 100mm STF has round, circular-shaped highlights and smoother background blur. Some people might prefer the more structure and highlights in the more traditional lens design bokeh, and others might prefer the STF bokeh.

Foreground blurring is also incredibly smooth, and there is minimal “double bokeh” when foreground blur blends into background blur.

This lens is excellent for taming both backgrounds and foregrounds, letting the subject shine instead of distracting from the main focus.

Summary

Pros

  • Dust and moisture resistance
  • Optical image stabilization
  • Silent, accurate and fast autofocus
  • Very sharp image quality
  • Extremely smooth background blur
  • Little to no chromatic aberration
  • Light vignetting wide open

Cons

  • T5.6 transmission can be limiting
  • Expensive at $1500

This lens seems so specialized from its specifications that we initially dismissed it, but after using it, we couldn’t help but adore it. If there’s one word to describe this lens, it’s special. The way the lens renders the world is so natural and smooth, but without comparing it side-by-side with other traditional lenses we wouldn’t even notice it. We would just notice the super sharp subject which melts into the background in a dreamy three-dimensional and seemingly effortless way. Maybe it’s just because it’s still new to us, but when we use another lens, it makes us miss the 100mm STF.

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