Pentax smc D FA 100 mm f/2.8 Macro WR
9. Ghosting, flares and transmission
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As you see the graph is very flat and even in a wide range of wavelengths - from about 450 to almost 700 nm. It means the Pentax’s optics renders colours well and doesn’t feature any unwanted casts. The maximum transmission reaches 91-92% which is a good, but only good, result. Taking into account the fact that we deal here with sixteen air-to-glass surfaces we can easily calculate that about 0.5% of light is lost on one surface. Pentax has already shown in other tests that it can produce coatings which lose only 0.2-0.3% of light. If those coatings were used here the average transmission would amount to about 95-96%.
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Perhaps just because of that thriftiness on coatings the Pentax smc D FA 100 mm f/2.8 Macro WR doesn’t work against bright light very well. At the maximum relative aperture as well as on stopping down you can notice a distinct green-yellow light artifact – the colour which, on the transmission curve presented above, featured a slight dip.
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