Canon EF 70-200 mm f/4L IS USM
7. Coma and astigmatism
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The lens corrects the coma very well. It is very hard to notice the coma’s influence on the diode picture at 135-200 mm. It is visible at 70 mm but the effect is very modest. The usage of the converter doesn’t result in any defect boom.
The average astigmatism value for the 70-200 f/4L IS reached 5.7%.
The defect was less noticeable as the focal length increased from 9%
at 70 mm to 3.2% at 200 mm. When we add other optical combinations
using the converter, the astigmatism increased to 5%. The overall
outcome in this category is very good with a slight weakness at the
70 mm focal length.
