Sony FE 100mm f/2.8 STF GM OSS ( SEL100F28GM ) - Review / Test
Lens Reviews - Sony Alpha (Full Format)

Review by Klaus Schroiff, published August 2017


After having reviewed several hundred of lenses, there aren't too many new lenses that make me truly excited to be honest. However, the Sony FE 100mm f/2.8 STF GM OSS is surely one of them. The high level specs aren't all that hot as you may notice - a 100mm f/2.8 is nothing to write home about after all. However, that's the less interesting aspect here. The real story is described by the "STF" portion in the lens name. STF stands for "Smooth Trans Focus". STF lenses feature an apodization (APD) element - a graduated neutral-gray filter element. The idea behind it is to soften harsh edges that can be present in the bokeh (out-of-focus blur). We'll have a look at the effect later on but as you may conclude from the presence of a gray element, it comes at a cost - light loss that is. In case of the Sony lens we are talking about 2 f-stops. This is expressed via a T-value (T = transmission) - thus it's a 100mm f/2.8 (T/5.6) lens. The T-value does not change the original "speed" (in terms of min. depth-of-field) of the lens - at least not at large apertures. To make things even more complicated regarding the f- and T-values, they range from f/2.8 to f/20 and T/5.6 to T/22 respectively. You may notice that the light loss is variable - at f/20 it's merely 1/3 of an f-stop because the dark outer portion of the filter is masked by the closed aperture. The camera will always display the T-value which feels a little unfortunate because such a lens is primarily about the depth-of-field rather than the effective speed so it's a little difficult to estimate the effect on the depth-of-field when stopping down. The lens is a member of the GM (G-Master) series - thus Sony's league of high-end lenses. You can certainly feel that when looking at its price tag of 1500 USD/EUR which is quite something for a 100mm f/2.8 lens ...

The build quality of the Sony lens is very good indeed. The lens barrel is made of sturdy, high quality plastics based on a metal mount. The physical length remains constant throughout the focus range. It's also weather-sealed. A fairly unusual feature is the dedicated aperture ring thus you can choose whether to change the aperture on the camera or on the lens. There are also dedicated switches for the AF and OSS plus a focus-lock button. Furthermore there are two dedicated focus ranges - "0.85m-∞" and "0.57m-1.0m". The latter gives you access to a maximum object magnification of 1:4 which may not quite touch the realms of a true macro lens but which may be "good enough" for many as far as close-focus applications are concerned. A deep barrel-shaped hood is also part of the package.

Sony uses its Direct Drive Super Sonic Wave AF Motor (DDSSM) in this lens. Maybe it's related to the already mentioned light-loss from the APD element but the AF speed is rather moderate. Typical for E-mount lenses, manual focusing works "by-wire". The focus precision is excellent.
The lens may be slow due to the dampening effect from the APD element but this is at least partially compensated by the OSS (Optical Steady Shot). The OSS can also be combined with select camera's sensor-shift type image stabilization. On the A7R II we'd rate the image stabilization efficiency between 3 to 4 f-stops.

Optical construction14 elements in 10 groups inc. 1x ED, 1x aspherical and 1xAPD elements
Number of aperture blades11 (circular)
min. focus distance0.57m (1:4)
Filter size72mm
Hoodsupplied, barrel-style, bayonet mount
Other featuresFocus Hold Button, Weather Sealing, Nano AR Coating, Focus Limiter, Aperture Ring, OSS

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