Let’s start with a transmission graph which we measured using a spectrophotometer.
As you can notice, the maximum transmission, amounting to about 85%, is reached for red light. In the centre of the visible spectrum and for blue light we get values near 80-82%. These results are hardly impressive. To assess them in the right way we must find out how the coatings of the tested lens work on one air-to-glass surface. There are 22 of such surfaces in the tested Sigma which means the lens loses on one of them on average 0.7-0.9% of light. It is not a result you can boast about. The best producers can reach the value of 0.2% and even Sigma itself showed many times that they can produce better coatings.
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Taking into account average transmission results, can we count on a good performance against bright light? Unfortunately the answer is no. The result is even more surprising because Sigma proved time and again it can produce lenses working perfectly well against bright light. Here we deal with a total failure and it can be seen in the photos below very clearly.
