Diopters are somewhat of a miracle with anamorphic lenses. My Tokina +0.4 helped cut the minimum focus distance of my Isco down to less than 4ft from 2 meters and helped sharpen it up at fast apertures like F1.4.
Pictured: Unique-in-the-world (factory custom job) Iscorama with aspherical elements from a Leica Sumicron.
More: anamorphic treasure on Flickr
Buy: 72mm Tokina +0.4 Diopter on eBay from a London based cinematographer
Diopters or achromats dramatically improve the sharpness and minimum focus distance of anamorphic lenses.
A Tokina double element diopter has transformed my Isco Centavision anamorphic to the point where it rivals the Iscorama 36 for sharpness. It has halved the minimum focus distance of the lens from 2 metres to 1.