Today is the third of three parts in this lens comparison. See Part 1 for the evaluation of center sharpness as well as a description of the lenses. Part 2 looks at edge sharpness.
In the previous two parts of this evaluation, I took a look at center and edge sharpness of these twelve lenses. Today I’m going to take a look at bokeh. Bokeh, as you likely know, means the quality of the out of focus portions of an image. It is a highly subjective characteristic, and you’re likely to find a huge disparity of opinions on what makes ‘good bokeh.’ While these lenses ability to blur the background more or less depending on their maximum aperture and focal length, the quality of these areas can still be evaluated. I will be looking at performance wide open as well as with all lenses stopped down to f/5.6.
The test setup is the same as in Part 2. The lenses were focused on a book in the foreground, about 1m away. The background was set up to allow evaluation for the rendering of certain types of background objects. One major aspect of bokeh is the rendering of specular highlights. To evaluate this, I placed a crystal decanter approximately 2.5 feet behind the focus point. Another 4 feet behind that, I placed a book with a diamond pattern on its cover to evaluate how the lenses defocused a repeating line pattern.
The crops below are not 100%, but rather a reduced frame resized to 600 pixels wide. This is large enough to objectively evaluate how these lenses render out of focus areas, but not so large that you can’t effectively move around to compare the lenses against each other. You will notice that the relative size of the objects varies from lens to lens. This is due to the different focal lengths of each lens. While the framing of the shot in focus was adjusted to have the book at the same size, the longer focal length lenses will have a narrower field of view, and therefore they enlarge the background when compared to shorter focal length lenses. This is one main reason why longer focal length lenses with the same aperture will blur the background more than a shorter lens, even with the same subject framing.
You may also notice that the Olympus 45mm and Olympus 40-150mm lens shots have the flower vase in a slightly different position. When I first conducted the test, I offloaded the images, and I noticed some issues with the original photos I took with these two lenses, so they needed to be reshot. The vase, however, had been moved when I cleaned up a bit, and when I replaced the objects, the vase ended up closer and to the left of its original position. The decanter and book, however, remained at the exact same distance relative to the shot, and so the bokeh shots remain valid here…just don’t use the flowers as an evaluation point.
Please click the images below to enlarge to full size. Due to the larger areas for evaluation, the images below are rather large. Please magnify them to full size after clicking and scroll around the screen to view all the crops.
Observations/Conclusion
This is a highly subjective property, so the best bet is for each individual person to decide which look they favor. I will give you my thoughts, however.
Wide open: Again the Olympus 45mm f/1.8 shines. In my opinion, it has the best overall bokeh wide open, with evenly rendered specular highlights and smooth gradation on the book cover. It maintains image contrast without being busy, and is very pleasing to my eye. The Leica 45mm also excels here, having a smooth rendering and a little character, showing a cats eye shape in parts of the specular highlights. Of the legacy lenses, I’m partial to the Hexanon 57mm f/1.2, which of course gives the most blur due to its longer focal length and large aperture. The specular highlights have a bright edge on one side, and there is a little bit of longitudinal chromatic aberration seen, but the blending of colors and contrast is superb to my eye. The FD 50mm f/1.4 also performs well. Specular highlights have a light ring, but the line rendering is the best of all the lenses in my opinion. On the not so good end, the Hexanon 40mm f/1.8 does fine on the specular highlights, but renders the book cover too harshly for my taste. The Rokkor 50mm f/1.4 has the harshest specular highlights to my eye, with obvious bright edge ringing around the highlights and noticeably color fringing as well.
At f/5.6: Stopped down a bit, the character of the bokeh changes for several of these lenses. While the Olympus 45mm doesn’t have too many individual faults, the high image contrast in the background leads to a distracting prominence of the book diagonals. The Leica 45mm handles this much better. This is a good thing, as the Leica 45mm is a macro lens, where stopped down use is common. The Panasonic 14-45mm turns in a rather pleasing performance, now that we see the other lenses at the same aperture. The Hexanon 57 is also rather nice, though the longitudinal CA appears more distracting here than at wide open. The Rokkor 50mm improves quite a lot stopped down, with no major artifacts and a generally pleasing rendering. The surprise winner in my opinion is the Petri 55mm. The aberrations that make it the softest lens in the sharpness category help it a lot in out of focus areas. This lens renders a smooth even look to the book lines, and most of the specular highlights are also well rendered, though the hexagon shape of the aperture is visible. There is also a slight onion effect in the specular highlights, but for the most part they look very nice, especially on the lines of the crystal decanter.
Final conclusion: Looking at all three tests presented here, I think it is safe to say that the Olympus M.Zuiko 45mm f/1.8 is the winner of this challenge. It is right up with the sharpest lenses in the center, both wide open and stopped down (and is easily the sharpest wide open of all the f/2 and faster lenses), and is absolutely head and shoulders above all the other lenses in edge performance. Throw in the nicest bokeh wide open and you’ve got an amazingly good portrait lens that will do wonders stopped down for critical short telephoto work as well. While not tested here, I can assure you that infinity performance of this lens does not suffer either. It’s an amazing optic. I will be doing a full review of the Olympus45mm f/1.8 in the next few weeks.
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