In this pair of articles I'll present one of my typical lens "tests", which involves shooting at different apertures in a controlled environment, and then roaming about the neighbourhood to take snapshots. The handling of the lens as well as its image quality will be under review.
The "Olympus G. Zuiko Auto-S 40mm F1.4", to give the lens its full title, was designed for the Olympus PEN F half-frame film camera, introduced in 1963. The innovative work of Yoshihisa Maitani (which involved over 50 patents) created an elegant well-built system that was immediately popular and sold millions. I happen to think it's one of the finest looking cameras you can get (the earlier Olympus Trip cameras are nice as well). Thus it was a pleasant surprise when Olympus tapped into this heritage to introduce their Micro Four Thirds cameras, about which I have been writing a fair amount lately. (Though in some ways technically superior, the Panasonic MFT cameras have the same old uninspiring SLR look.)
Unfortunately Olympus have not been offering lenses with the same flair (I must be sure to spell that correctly!) as their old Zuiko optics. So I have resorted to finding legacy lenses on "the internets", an annoying process that involves out-bidding thousands of other photographers with similar thoughts. But sometimes you find a deal (this being the carrot to the internet mules -- but I digress).
At this point you might want to look back at Choosing An Alternative Mount Lens for an ILM Camera for how I narrowed my lens search.
The G. Zuiko 40/1.4 is one of the most popular choices for lenses to adapt, since it offers an excellent optic in a compact size (43mm in length and 165g) -- and it has a fast maximum aperture. It requires an inexpensive ($20) and tiny 9mm adapter for use on MFT bodies.
First, I set up the Olympus E-P1 on a tripod with the timer function, using natural light on an overcast day when illumination was not varying. Using the close focus distance of 35mm, I focused on an arrangement of seashells, so the effects of depth of field and bokeh could be seen. Here are the results for each stop from f/1.4 to f/4. You'll want to click through to Flickr to see them larger. If you do, check out the adjacent images for the remainder of the stops.
The results are agreeable. The slight softness seen wide open disappears by f/2.8 and the bokeh is at all times pleasant. The lens does not appear overly contrasty and the colours are not as vivid as with my Pentax lenses, but I am quite used to that result. These qualities can be "pumped up" in post-processing, should needs be. Indeed, using my usual RAW conversion profile, the wide open result is as follows:
From this I conclude there is no problem with the lens in this regard. All digital images need appropriate post-processing just as all film stocks need appropriate development.
This aperture test did reveal one problem, however, which can be seen starting with the shot for f/5.6. The image is too dark. Subsequent apertures only get worse and the conclusion is inescapable: the camera is not exposing correctly for the lens. Since I do not have this problem with any of my adapted K-mount lenses I cannot tell if the problem is the camera body, the adapter, or the lens itself. Certainly it appears to stop down properly when I do so manually (lens off camera). This is both perplexing and annoying in general use. By f/16 and exposure compensation of about +1.7 is required -- here are the uncorrected and in-camera corrected exposures:
Now I will present the results of the bookshelf test. learning from the previous exercise I compensated for the exposure so as to get comparable results. In this case I discovered that I needed to begin compensating immediately and consistently on stopping down, adding one-third of an EV positive compensation per stop. In practice this will be annoying and definitely sap some of the joy of using the Zuiko.
As you can see, the white balance was off, so this was not an effective test of colour rendition. In other regards it conforms with the results from the first test.
Finally, here is a strip of 100% crops from the centre of the image. I have uploaded the full-sized image so those of you who are interested can download the entire thing. This image has been colour-corrected, but is free of any other processing. As you can see, even wide open the texture of the spine to the right is visible, though small and medium level detail definitely improves with each stop to f/5.6, after which the effects of diffraction slightly limit detail and contrast. (These empirical results conform with the theoretical value of f/4.5, as presented in Choosing An Optimal Aperture To Avoid Diffraction.)
Join me soon for Part 2, in which I present some real-world shots and my subjective impressions of the lens.