Lens review

Carl Zeiss Distagon T* 35 mm f/2 ZF/ZK/ZS/ZE

25 June 2009
Arkadiusz Olech

9. Ghosting, flares and transmission

In full name of the Zeiss Distagon there is a T* symbol which is well-known to every photo enthusiast. It’s of course a legendary sign of a lens multi-coating and an anti-reflection coating from the Zeiss. The manufacturer assure that this coating guarantees no more than 0.2% reflected light from a single air-glass boundary. Using a spectrophotometer we could prove whether it is true or not. A transmission curve of the tested lens you can find below.

Carl Zeiss Distagon T* 35 mm f/2 ZF/ZK/ZS/ZE - Ghosting, flares and transmission

Well.. also this time we admire a craft and skills Zeiss’s opticians and engineers. The transmission curve is exemplary. In a green, yellow, and red range it gives flat line achieving 96-97%. The lens construction consist of 7 groups so it creates 14 contact spaces air-glass inside which means that Zeiss engineers didn’t lie asserting that the Distagon waste only 0.2% light passing through the lenses and air. The only disadvantage is a low transmission in a blue and violet spectrum where decreases to 80%.

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A very intriguing phenomena is local maxima and minima on the curve. It illustrates how the antireflection coatings function one by one.

Although during the working against bright light the Zeiss is free of extensive flares, on a larger as well as smaller aperture flare patterns are still noticeable. At f/2 and slightly above, towards the source of bright light, we noticed two green artifacts and a reddish glow. It only shows that even the best anti-reflection coatings are not the only way to completely eliminate the flaring.

Carl Zeiss Distagon T* 35 mm f/2 ZF/ZK/ZS/ZE - Ghosting, flares and transmission