Olympus Zuiko Digital ED 12-60 mm f/2.8-4.0 SWD
9. Ghosting, flares and transmission
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Olympus ZD 12-60 mm contains 10 groups of lenses, so it means that there are 20 air-glass boundaries to cover with antireflex coatings. These coating have to be really good if we want from the instrument to give a flat transmission profile on a high level. How does it look in case of Olympus ZD 12-60 mm, we can see in the picture below.
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We get the highest transmission at 92% level for the red light. It means that around this wavelength there is 0.4% of light lost on each boundary. It's a very good result, although not the best one. We already know the coatings which reflect only 0.2-0.3% light on one surface. What may concerns a little, is a slow drop of transmission level in the shorter wavelength range. In the middle of the visible spectrum it reaches the level of 90% and in the blue light drops to only 85%. It's not a bad result, but we would expect something more from the lens of such a high class. For example Sigma 24-70 mm f/2.8 HSM lens got 2-3% higher result in this category and in its case there were 4 additional air-glass surfaces to cover.
