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HD-EC Anamorphic Converter ACV-235
The ACV-235 is an innovative new cine accessory offered by Canon. It is an optical converter that connects between any 2/3-inch cine lens and any 2/3-inch digital motion picture camera to allow a wide 2.35:1 aspect ratio image to be captured with the presently standardized 16:9 high definition imagers. It is the world's first anamorphic converter specifically developed for the 2/3-inch HD format.
This converter is intended for directors and cinematographers who use digital motion picture systems and standard 2/3-inch cine lenses for production of widescreen feature movies.
ABOUT THIS CONVERTER
The ACV-235 offers an important new alternative to managing very widescreen images for motion picture feature release. Typically the 16:9 image format 24P digital motion picture systems have dealt with cinemascope TM 2.35:1 aspect ratios by appropriate protection during principal photography and then by subsequent digital cropping (during postproduction) to produce the desired 2.35:1 imagery from the original 1.78:1 capture. This entails a penalty in vertical resolution (there being approximately 800 scanning lines of active picture remaining as a consequence of the cropping process instead of the original 1080-line capture). With the 720-line HD format this would reduce the final image to about 550 lines vertically.
Canon responded to the exhortations of some directors of photography who wanted to freely use a wide range of standard 2/3-inch cine lenses but achieve a 2.35:1 filmout with maximum overall picture sharpness. The ACV-235 is an optimum solution to this challenge.
The ACV-235 converter is premised on the desire to retain all of the vertical resolution of the lens-camera system. It applies a horizontal optical compression of 1.33 times and thus produces at its output a 16:9 image having a squeezed horizontal dimension that is effectively 2.35 times that of the vertical dimension (1.78 x 1.33 = 2.35). While this compression does entail its own modest loss of horizontal resolution, the overall image sharpness (especially when viewed on a large screen) is approximately 1.3 sharper than the cropped image approach. This is because there are 1920 horizontal samples versus the 1080 vertical samples within the 1080-line format - and there are 1280 horizontal samples versus the 720 vertical samples within the 720-line format.
Anamorphic optical converters are not new. The motion picture film industry has regularly used anamorphic lenses (often termed "front" anamorphic) to achieve a variety of wide screen formats. Technically this is a more simple design in making a large field of view more attainable and it allows classic cylindrical lens design. The great advantage of the "rear" converter is that it can be used with any standard cine lens - prime or zoom. The design is, however, more challenging than the anamorphic lens.
The converter design has achieved a very high MTF that is optimally distributed across the image plane. Combined with the superb contrast performance and a remarkably well-controlled relative light distribution characteristic, the resultant picture sharpness contributes to imagery of extraordinary clarity.
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