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Camera Lens News No. 13
Spring 2001 |
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Do you Lose or Gain with the CLA 35 HD by Angénieux and Zeiss?
In the eyes of many cameramen and salespeople the Cine Lens Adapter CLA 35 HD by Angénieux and Zeiss resembles a ”converter”. This concept, and this term, remind them of ”teleconverter” and they then begin thinking, ”These devices give a magnified image, but at the cost of reduced lens speed and often, significantly reduced image quality.” With these thoughts in mind, they might be reluctant to try or to promote the CLA 35 HD. How will the CLA 35 HD do in these respects. Is it worth their effort?
So let us add some factual information from Zeiss to expand on what the CLA 35 HD leaflet from Angénieux and Zeiss already states:
The primary job of the CLA 35 HD is to allow the use of high quality cine lenses like the Zeiss/ARRI ULTRA PRIME set used in 35 mm motion picture production alongside the new Angénieux zoom lenses, with the latest 2/3" high definition electronic cameras.
This is not an easy task and goes far beyond mere mechanical or simple optical adaptation. Cine lenses are designed to send their picture direct to film – without any optical detour – whilst lenses for electronic cameras send their images through a beam splitter first, in order to allow generation of color in the electronic image. To meet these requirements, Angénieux and Zeiss had to incorporate 12 lens elements, some made of extremely challenging optical materials, assembled and aligned with utmost precision in 10 groups. The result, however, is quite rewarding.
The image dimensions in a 2/3" electronic camera are 2.5 times smaller than a frame on 35 mm film. So the CLA 35 HD has to compress the image dimensions by a factor of 1:2.5, (0.4x) and, at the same time, take care of the optical properties of the beam splitter device in the camera.
Since the CLA 35 HD does not expand the image like a teleconverter would, but rather compresses it, the effect on light transmission is the opposite. The CLA 35 actually enhances brightness. The explanation is simple. All the energy which would be distributed over a larger 35 mm film frame by the prime cine lens is concentrated onto the much smaller frame of a 2/3" CCD chip. The resulting effective gain is 2.5 stops! Thus an f/4 cine lens is converted by the CLA 35 HD into a f/1.6 video lens. (with inevitable slight losses due to the greater complexity of optical system.)
And how about resolution? On the optical test bench, Zeiss/ARRI ULTRA PRIME lenses typically produce resolutions of 200 lp/mm (linepairs per millimeter) and beyond. (Don't be misled by the fact that Zeiss data sheets plot MTF graphs only for up to 40 lp/mm!) This is much more than the highest resolving film stock currently available can process (around 160 lp/mm). So the performance of these lenses has ample reserves. Transferred through the CLA 35 HD with the compression factor of 2.5x we climb toward the stratospheric (theoretical) resolution of a stunning 500 lp/mm!
We do not claim that such extreme resolution is required in digital imaging in the foreseeable future. But we do know for sure that microstructures on semiconductors are made today using Zeiss lenses that resolve 5.000 lp/mm (although in monochromatic deep UV light. See CLN No. 12!
Publishing these figures here serves just one purpose: To make clear that the CLA 35 HD is not likely to create a bottleneck when it comes to sharpness. First independent tests in the lab of a renowned film camera manufacturer showed results which clearly support our point.
In short: Since the CLA 35 HD focuses the optical quality of an already excellent 35 mm cine lens by a factor of 2.5x onto a much smaller frame on a 2/3" CCD chip, the image quality parameters of the resulting picture are extremely good. | |
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