On the one hand a construction consisting of 19 elements positioned in 14 groups is very impressive, making us think with respect about the task before the engineers and optics specialists working for Olympus. On the other hands, though, you cannot cheat laws of physics. With an optical system that features as many as 28 air-to-glass surfaces you can be practically sure there will be problems even if you assume that the producer employed anti-reflective coatings of the best quality so those which lose only about 0.3% of light on one surface. It means that overall loses will be still almost 10% or higher. You should remember that those 0.3% concern only rays falling straight and the center of the visible spectrum. For bigger angles and other wavelengths that value should be increased 2-3 times. Additional percent or two will be also lost due to the light absorption of glass. Even though we didn’t manage to measure the transmission of this lens with our spectrophotometer I would be actually surprised if its complete transmission reached 85% in the center of the visible spectrum.
What happens to that lost light? Photos below show it very well. We took two shots, one after another, using two Olympus lenses: the 1.2/25 model, tested here, and the Olympus 3.5/30 Macro, much simpler when it comes to the optical construction (just 6 groups of elements). In both cases the photos were taken at the maximum relative aperture. The difference in contrast is evident and when the overall contrast of a photo decreases, so do the MTF50 values which are, after all, a result of the measurement of the contrast gradient across an edge. It is also one of the reasons why the tested lens, despite excellent parameters, didn’t manage to break any resolution records.
Photos below show that, apart from contrast loss, you can catch a lot of flares and ghosting - the more you stop down the aperture, the more pronounced the problem becomes. When the sun is situated inside the frame or close to its corner the number of artifacts is the biggest. After you move the sun outside the frame the problems become less acute but they don’t disappear completely.
