Why are uncoated lenses a thing now? Well, it may be due to the attractive nature of older lenses that are now in high demand, such as anamorphic lenses from the sixties. These uncoated lenses provide softer images with options for less contrast, internal flares and reflections. Janusz Kaminsky stripped the lens coating off his Panavision Ultraspeed primes to achieve the kind of combat photographer feel for Saving Private Ryan, and Hoyte Van Hoytema used uncoated lenses on Her to achieve that kind of uncoated and naked aesthetic.
Originally featured on the Mini S4i line, the new uncoated S4/i lenses are designed to give maximum performance at full aperture with superior control of flare, distortion and spherical aberration. They will be available for prime lenses ranging from 12-300 mm.
In addition, Cooke says that shooters will be able to organise their front elements individually for even more options, essentially creating two lens choices in one depending on the overall look a cinematographer is trying to achieve.
Cooke also says that existing owners and rental houses that offer S4/i primes in their kits can bring their lenses in to have the front elements changed out for uncoated options by trained Cooke lens technicians. The lenses may also need to be re-shimmed and the focus scales re-calibrated to correct for what amounts to a slight loss of light of about 10%, depending on the lens being changed. A lens with a maximum T-stop of T2.0 with an uncoated front element will become a T2.2 lens due to less light streaming in. But the results will be a more vintage look due to natural aberrations that can provide a more dramatic and artistic feel. Not a bad trade off.
Cook also warned that the front element may end up stained or discoloured over time since it will be uncoated. caveat emptor.
Have a look at the video below illustrating the difference between coated and uncoated on a Cooke MiniS4.