The Optimo 15-40 shows a soft fall off that might work pretty well in 1.85 but would need to be tested with actual images to determine if you like the effect.

Optimo 15-40 at 15mm on Alexa XT Open gate

Optimo 15-40 at 15mm on Alexa XT Open gate

Optimo 15-40 at 15mm on Alexa XT Open Gate with 1.85 crop

Optimo 15-40 at 15mm on Alexa XT Open Gate with 1.85 crop

Optimo 15-40 at 40mm on Alexa XT Open Gate

Optimo 15-40 at 40mm on Alexa XT Open Gate

Optimo 15-40 at 15mm on Alexa XT Open Gate with 1.85 crop

Optimo 15-40 at 15mm on Alexa XT Open Gate with 1.85 crop