Olympus PEN F 25mm f/4 Half-Frame
Here is a compact wide angle lens for the Olympus half-frame SLR camera. So how is it with the modest f/4 aperture?
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 42mm 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 38mm f/1.8 lens. This makes it a nice fairly compact wide angle. 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.
The lens has 5 elements in 5 groups, and has only a 5 bladed diaphragm, which is mostly circular at large f/stops and mostly pentagon at smaller f/stops. The minimum focus distance is a short 0.25 m (9.8 in), and is fairly dense at 120 g (4.2 oz). Filter threads are standard 43 mm. Some of the slotted 43mm rangefinder hoods for the wide standard lenses (like Cosina Voigtländer 40mm f/1.4) will work on this lens.
Optical Characteristics
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Comments on the Results
Center 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. is very good wide open, but does drop off towards the corners. 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. is relatively good across the frame at all apertures. One thing I notice in my test images is the very extreme corners are soft at f/4, better by f/5.6, and very good by f/8. This is the very tip of the corner, slightly out side of the region measured by my chart.
Distortion is a modest -1.1% barrel (numeric average for all apertures).
Lateral CADifferent wavelengths (colors) of light have different magnifications and produce colored halos around high contrast objects near the frame edges. is fair, pretty typical for a wider 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 visible on a chart, but fairly negligible due to the small aperture.
ComaPoints of light are distorted near the edges of the frame. A circular point of light might be more comet shaped. is fairly minor. It is pretty much gone at f/8. There is some 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. too, which improves on stopping down.
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. is negligible.
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., as expected for this vintage lens, is very noticeable. If the sun is in the frame it will mostly likely produce reflections. 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. isn’t bad, contrast remains fairly decent with contra lightA term for a strong back light that can lead to 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. or 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.. An example is placing the sun behind a subject..
Measured focal length 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.: 26.5 mm and at infinity it was 25.9 mm.
Bokeh, please see the samples as this is personal taste. There are some bright rings on some of the specular highlights wide open.
I notice a slight 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. on the sides of the frame on my NEX 3. If I get a NEX 5n, I will test it on there to see if it goes away.
Pros and Cons
- Performance across most of the frame
- Small Size
- Easy to Focus
- Small Aperture
- Extreme Corners wide open
- Slight 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.
Bottom Line
Let me preface this by saying I really like the images from the lens. However, it doesn’t offer that much over a kit lens. The aperture is relatively small, and the lens is susceptible 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.. However, it is a joy to use. The focus with the peaking function works very well at this aperture, focus is smooth, and the lens is very easy to use. The images are nice straight from the camera. In terms of 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. and 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. it performs a bit better than the SEL 30mm f/3.5 macro, but has similar characteristics. If you like old manual focus lenses, this one is a lot of fun. The reason to buy this over an SLR lens is the shorter adapter length and smaller diameter.
Gallery
The gallery images are © 2011 Eric Tastad, and may only be used for personal evaluation of the lenses. You can visit the
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