OWC Drive Dock for backup drives or extra storage.
USB-C about $119
USB 3.1 about $75
Thunderbolt 2 + USB about $180
Zeiss 15/2.8 Distagon Q&A — Distortion
Related: distortion, Hubert Nasse, optics, wide angle, Zeiss, Zeiss 15mm f/2.8 Distagon, Zeiss Distagon, Zeiss DSLR Lenses
This is one of several pages resulting from the March 13, 2012 discussion with Staff Scientist Dr. Hubert Nasse. See the original list of questions.
These pages are a summary of the discussion based on notes taken, and as reviewed by Dr. Nasse. Bracketed comments [ ] are editorial in nature.
Low distortion was a design goal for the 15/2.8 Distagon. In particular, a distortion goal of 2% was desirable, and also to avoid a wave-type distortion as found with the 21/2.8 Distagon (one of its few faults).
The 15/2.8 Distagon succeeds with only 2% barrel distortion, which is usually undetectable by the eye. For critical uses, barrel distortion is straightforward to correct in post processing.
For very close work near to 1:9, the distortion rises, but with such close focusing, the perspective is often the dominating factor. Note that a 1:9 reproduction ratio involves a sensor to subject distance of only 25cm (10 inches), and that affords only 9cm / 3.54" of clearance to the front lens element! Users working at such close range might consider using a filter to protect the front lens element from mishaps.