Sony has a specialist in the lens line-up for portrait and macro photographers and for the lovers of a shallow depth of field (Bokeh): the Sony 135mm F2.8 [T4.50] STF. This article describes the special characteristics of this lens and tries to compare the STF with the Sony FE 70-200mm F4 G OSS, both on an ILCE-7, because Sony has equiped the FE 70-200 with a little speciality for a nice bokeh. Additionally, two older manual focus lenses (Pentacon 135mm F2.8 on a7 and 85/2 MC Jupiter-9 on a6000) get the chance to compete against the STF and the FE 70-200mm F4 to show what they are capable of. The verdict verifies some myths and gives a recommendation which lens is suitable for which type of photographer. All pictures and crops of the bokeh comparison are provided for download at the end of the article to provide the opportunity to look at these pictures in full size and resolution on the own screen to build your own verdict.
The Sony 135mm F2.8 [T4.5] STF (referred to as STF in this article), also know as SAL 135F28, was released by Minolta in 1999 and was revised by Sony in 2006 with very small changes. Except a slight change in used materials for the plastic parts with a reduction in weight of 82 gramms and a different choice in colors for aperture ring and the distance scale nothing else has changed with this lens and its construction. The STF was build with one special aim: create a very soft and smooth out of focus area in front of and behind the focus plane independent from the distance to the focus plane. Therefore this lens has two adjustable apertures. The automatic aperture with 9 blades is used when the aperture control ring is set to „A“ and is changed through the aperture setting of the camera like with other lenses. Secondly the STF has a stepless aperture with 10 blades, which is controlled through the aperture ring. In addition to the two apertures with 9 and 10 blades, the lens has a so called apodisation filter, which is a special, concentric gray gradient filter with maximum transmission in the middle and decreasing transparency to the edges. This element reduced the amount of light towards the edge of the lens from 0 aperture values in the middle towards 1.5 aperture values at the edge of the element resulting a transmission value (T) of T4.5 at open aperture. The apodisation filter creates a natural softening of the edges of an object without artificially changing the original shape of the object.
What is so special about the FE 70-200 F4 G OSS? Next to the FE 55mm F1.8, this lens is the only one in the current FE line-up equiped with a circular aperture with 9 aperture blades. This aperture contruction creates a circular aperture and a nice bokeh over the entire aperture range from f/4 to f/22 – so the promise of Sony. In comparison to the STF, the FE 70-200 has a few features not found with the STF like the optical stabilisation OSS and SSM for fast autofocus with super sonic drive.
2. Retrospective 2011
I made the first comparison of the STF with the SAL 70-200 F2.8 G SSM I shortly after I bought the STF in 2011 using an a850 and then already to find out whether the loss of autofocus and flexibility in reference to focal length is worth the difference in bokey. The graphical material for this article has been put side by side in the compare view of Lightroom.
The following pictures compare the STF using the automatic aperture in A-Mode with the SAL 70-200. The shown aperture value (f/x) of the STF is the effective transmission value (T/x) which is 1.5 aperture values higher.
The following comparison refers to the STF in T-Mode with using the second aperture with 10 aperture blades.
Summarising the above shown pictures, it is quite obvious that the STF is rendering a better bokeh in A-Mode with automatic aperture up to F4.5[T6.3] than the SAL 70-200 at F6.3. Above T6.3 the STF is showing first weaknesses in bokeh. In T-Mode using the second, manual aperture the pictures show clearly that this should be the preferred mode of the lens. These last pictures certainly explain why this lens is still in my gear after my switch from Sony A-Mount to E-Mount cameras.