Olympus G.Zuiko Auto-W PEN F 20mm f/3.5 OM on NEX 3
This is a nice compact wide angle, much smaller than any adapted SLR lens of similar coverage, 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 47 mm with the adapter and lens. The adapter also tapers down and the lens is only about 46mm in diameter. This appears to be in the same barrel as the 40 mm f/1.4 lens, which is about 5 mm longer than the 38 mm f/1.8 and 25 mm f/4 lenses, but still nice and compact. Build quality is superb, with all metal construction, nice smooth focus and aperture ring. I find the front aperture ring easier to use than some of those next to the body.
Same as with other PEN F lenses, you can pull out (towards the objective element) on the aperture ring and spin it around so you can control in specific aperture numbers (f/3.5, 5.6, 8, 11, and 16) or you can use f/stops relative from wide open (0, 1, 2, 3, and 4)
The lens has 7 elements in 6 groups, with a 5 mostly straight (slightly curved) bladed diaphragm. The minimum focus distance is short 0.2 m (7.9 inches), and the weight is light at 145 g (5.2 oz). It uses rangefinder standard filters of 43 mm.
Optical Performance
Please click on the tab you want to view. Only 1 tab may be active at a time. MTF, Distortion, and Lat CA data acquired using
ImatestComments on the Results
The lens exhibits a lot of field curvature so you want to focus where you want it sharp. The corners are pretty mushy wide open, and even stopped down to f/5.6 or 8, but if you focus for the corner resolutionI use the term resolution to refer to the MTF20I use the term resolution to refer to the MTF20 graph. This is how well the lens can resolve fine detail, but the contrast is low at this point. graph. This is how well the lens can resolve fine detail, but the contrast is low at this point. is okay (it still lacks contrast though).
The lens has noticeable barrel distortion, but is less than the new Sigma at 1.2% barrel.
Lateral CADifferent wavelengths (colors) of light have different magnifications and produce colored halos around high contrast objects near the frame edges. is noticeable, but not bad for a wide angle lens. Longitudinal CADifferent wavelengths (colors) have different focus points, causing colored halos in out of focus regions of the image; typical is magenta in front of focus plane and cyan behind. is hardly noticeable. Unfortunately corner shading is an issue. Vignetting is high, and there is a color shiftThe colors towards the edge of the frame are different from those near the center. This can occur when the lens is very close to the sensor. Different wavelengths of light are not absorbed as well when it hits the sensor at a large angle near the edges of the frame..
I don’t notice much purple fringingPurple fringing occurs around high contrast edges in a lens with high longitudinal CA in the focused areas; the slightly out of focus red and blue are fairly balanced and combine to create a purple halo. The sensor microlenses and color filter can aggravate purple fringing as well.. Lightroom 4.1 allows for correction of longitudinal CADifferent wavelengths (colors) have different focus points, causing colored halos in out of focus regions of the image; typical is magenta in front of focus plane and cyan behind. and it does a good job, as long as you don’t overdo it and there aren’t strong colors behind the fringes that will desaturate.
ComaPoints of light are distorted near the edges of the frame. A circular point of light might be more comet shaped. and astigmatismDifferent angle edges have different focal points. A picture of an X might have one / of the X sharper than the other \. Has the appearance of slight motion blur or softness, and tends to be worst at the edges of the frame. are visible, lights in the corners are comet shaped, and line sharpnessI use this to refer to the MTF50I use this to refer to the MTF50 graph. This is how contrasty the lens is, and correlates with perceived sharpness. A lens with high MTF50 will have a short transition period between a white and black edge. graph. This is how contrasty the lens is, and correlates with perceived sharpness. A lens with high MTF50I use this to refer to the MTF50 graph. This is how contrasty the lens is, and correlates with perceived sharpness. A lens with high MTF50 will have a short transition period between a white and black edge. will have a short transition period between a white and black edge. depends on if it runs radially or tangent.
Resistance to iris reflections is low, and veiling glareA specific type of flareInternal reflections on the lens elements causes ghost images and other artifacts to appear in the captured image. Most common is internal lens elements and diaphragm shapes will show when a bright light source like the sun is in or near the frame. in contra light where the overall sharpnessI use this to refer to the MTF50I use this to refer to the MTF50 graph. This is how contrasty the lens is, and correlates with perceived sharpness. A lens with high MTF50 will have a short transition period between a white and black edge. graph. This is how contrasty the lens is, and correlates with perceived sharpness. A lens with high MTF50I use this to refer to the MTF50 graph. This is how contrasty the lens is, and correlates with perceived sharpness. A lens with high MTF50 will have a short transition period between a white and black edge. will have a short transition period between a white and black edge. of the image is reduced but resolutionI use the term resolution to refer to the MTF20I use the term resolution to refer to the MTF20 graph. This is how well the lens can resolve fine detail, but the contrast is low at this point. graph. This is how well the lens can resolve fine detail, but the contrast is low at this point. remains. Large glass elements, scratches, fungus, and poor/no optical coatings can lead to veiling glare. A lens hood can reduce this type of flareInternal reflections on the lens elements causes ghost images and other artifacts to appear in the captured image. Most common is internal lens elements and diaphragm shapes will show when a bright light source like the sun is in or near the frame. dramatically. is high. Not resistant to flareInternal reflections on the lens elements causes ghost images and other artifacts to appear in the captured image. Most common is internal lens elements and diaphragm shapes will show when a bright light source like the sun is in or near the frame..
Measured focal length is 21mm at 1:53 magnificationHow large an image appears on the image sensor compared to how big it is in real life. Life size magnification means the image is the same size as the real object. My charts are photographed at 1:53 magnification, so if I photograph an area 53" wide it would appear as 1" wide on the sensor..
Pros and Cons
- Similar performance to similar vintage SLR 20 mm
- Compact and well made
- FlareInternal reflections on the lens elements causes ghost images and other artifacts to appear in the captured image. Most common is internal lens elements and diaphragm shapes will show when a bright light source like the sun is in or near the frame.
- ComaPoints of light are distorted near the edges of the frame. A circular point of light might be more comet shaped. and AstigmatismDifferent angle edges have different focal points. A picture of an X might have one / of the X sharper than the other \. Has the appearance of slight motion blur or softness, and tends to be worst at the edges of the frame.
Bottom Line
I am split between yellow and green for this lens, but its performance is the same as the
Nikkor 20 mm f/3.5 and it sells for a similar price used and is a much smaller lens. About the only main weakness relative to the Nikkor is it has corner shading and color shifting typical of wide old short flange distance lenses on the NEX. I would give it a green rating, but for the color shifting. It has excellent center
resolutionI use the term resolution to refer to the MTF20I use the term resolution to refer to the MTF20 graph. This is how well the lens can resolve fine detail, but the contrast is low at this point. graph. This is how well the lens can resolve fine detail, but the contrast is low at this point., better than the Sigma 19 mm f/2.8, but it just isn’t as flexible of a lens overall, and field curvature requires you to be careful with your focus point or shoot at f/11. Typically, for non centered subjects focusing away from the center point and edges is best for a lens with field curvature, as it will average the
resolutionI use the term resolution to refer to the MTF20I use the term resolution to refer to the MTF20 graph. This is how well the lens can resolve fine detail, but the contrast is low at this point. graph. This is how well the lens can resolve fine detail, but the contrast is low at this point. between the center and the edges a bit. Buy this lens if you want a fun older lens to use, where you want
flareInternal reflections on the lens elements causes ghost images and other artifacts to appear in the captured image. Most common is internal lens elements and diaphragm shapes will show when a bright light source like the sun is in or near the frame. showing for character, etc.
Gallery
The gallery images are © 2012 Eric Tastad, and may only be used for personal evaluation of the lenses. Click the play button and click “visit gallery” in the upper right to download full size images.
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I had that exact same combination (20mm 3.5 on NEX 3) and also found that this nice little lens unfortunately did not perform to modern standards.
I found the Pen F 40mm f/4.0 to be much more usable for portraits.
An advantage Pen F lenses have, Pen F cameras being SLRs offering TTL focusing, is the much closer minimal focusing distance than other compact lenses (Contax G, Leica screw or M mount) designed for rangefinder cameras.