Olympus PEN F 42mm f/1.2 Half-Frame
This Pen F half frame SLR lens is not as small as the 38mm f/1.8, but is a full stop larger aperture. How does it perform?
The Olympus PEN F series lenses are compact lenses designed for a half-frame (135 format 35mm) film SLR, which conveniently enough is basically the same size as an APS-C digital sensor. The PEN F shot a vertical picture on a 35mm frame. The longer dimension was up and down on the film, this meant you had to shoot with the camera held vertically to get a landscape orientation shot.
Being a half-frame lens, it was designed with a much shorter flange distance than a traditional SLR lens, so the adapter on the NEX is only about 10mm thick, and an overall length is only 57mm with the adapter and lens (to mounting surface). The adapter also tapers down and the lens is only about 54mm in diameter. This is still noticeably, but not a lot, smaller than a 50mm f/1.4 lens and adapter from an SLR. This lens is going to be close in size to the upcoming 50 mm f/1.8 OSS which is 62 mm x 62 mm (about the same size as the compact Olympus OM 50mm f/1.8 with adapter). Given that this lens is 1 f/stop larger aperture, it is relatively compact.
The lens has 8 elements in 6 groups, and has an 8 bladed diapragm, with slightly curved blades. Even by f/2 it is looking fairly octagon. The minimum focus distance is a short 0.35 m (1.1 ft), and is dense at 255 g (9 oz). Filter threads are standard 49 mm (larger than other Pen F lenses).
Comments on the Results
This lens has very good center performance across the range, but also very strong field curvature. The charts above show the best values for sharpness achieved at each position. Focused for central performance, the corners will be very soft wide open. If you want across the frame performance at large apertures you will need to make a compromise between center sharpness and corner sharpness. However, by only f/2.8 has great resolution across the frame.
Distortion is very noticeable, but not extreme -1.6% barrel (numeric average for all apertures).
Lateral CA is not well controlled and is visible on shots. Longitudinal CA in the out of focus regions is noticeable at large apertures, but is pretty decent for this class lens.
Coma and astigmatism are fairly minor. There is noticeable optical vignetting (cats eye shaped bokeh and a spiral look to the bokeh) at large apertures.
Purple fringing is minor, but there is some visible wide open.
The lens is sensitive to flare.
Bokeh is subjective, and it does get harsh in some conditions, but overall I find it very pleasing. Not sure why it gets such harsh reviews online, as the bokeh of this lens is less questionable than the 38mm f/1.8.
Measured focal length at 1:53 magnification: 44mm
Pros and Cons
- Center Performance
- Entire Frame from f/2.8
- Extremely large aperture
- Corners/partway at large f/stops
- Field Curvature