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why are CCTV lenses for 2/3" CCD cameras not Super 16 safe?


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#1 Sir Alvin Ekarma

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Posted 13 July 2006 - 09:28 PM

Does anyone know why this is exactly?
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#2 Chris Keth

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Posted 13 July 2006 - 09:49 PM

Does anyone know why this is exactly?



Video and film lenses have historically been separate markets. Only recently have the two crossed in any large sense. Another reason could be that lenses made for 2/3 inch SD video don't need anywhere near the quality that lenses would need to record to super 16. Yet a third reason could be that lens mounts for the two media have generally been completely different and incompatible, so it didn't matter if they were compatible.
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#3 David Mullen ASC

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Posted 13 July 2006 - 09:53 PM

The 2/3" CCD is smaller than the Super-16 frame, so it may not cover the film frame without any vignetting. Beyond that, most video lenses are designed to focus light onto a prism block where the light is split three ways onto filtered sensors.
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#4 James Erd

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Posted 14 July 2006 - 02:06 AM

This is a bit off topic in a way but, I just went to a seminar on the Sony XDCam and they made the point that SD lenses are not up to HD quality. They showed some images shot on HD with SD lenses and you could see some chromatic aberration and the image was definitely softer. So even if you account for the coverage and the prism your probably not getting the performance you would with the correct lens. My take away lesson was that there is more to lenses than coverage, speed, and focal length, and if I'm going to spend the money for the film stock I'm going to get the best lens I can. Buy it, rent it, steal it what ever...
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#5 Jim Murdoch

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Posted 14 July 2006 - 05:22 AM

Does anyone know why this is exactly?

The term "2/3 inch" originally referred to the physical diameter of a vidicon or Saticon etc thermionic camera tube, not the diagonal of the actual scanned photosensitive surface. Because with electromagnetic scanning you can easily vary the size of the scanned image, there was no specific size this scanned area had to be, but generally, the recommended diagonal for 4:3 scanning was 11mm (0.44").

A "2/3 inch" CCD means one whose photosensitve area has a diagonal of 11mm, (which obviously can't be altered) and what that originally implied was that a lens designed to work with a "2/3 inch" camera tube could be fitted to a 2/3" CCD model and deliver the same sized image. This is particularly important in the CCTV industry because the cameras usually wear out long before the lenses do! All it really means is that a 2/3" lens is guaranteed to maintain focus at least over the 11mm diagonal area.

There are two answers to your question. The first, as others have pointed out, is that the image area of Super-16 is considerably wider than that of a 2/3" CCD, and so may suffer from vignetting, and the other is simply that most CCTV lenses just plain aren't good enough. Apart from the inherently low resolution of most NTSC or PAL CCTV cameras, all CCD cameras are fitted with a optical low-pass filter (AKA a "Spatial filter") to prevent aliasing artifacts, and because of that, making and using a lens past a certain sharpness level is pretty much a waste of money.

However, the inherently higher resolution of film (and HD cameras for that matter) soon shows up their deficiencies.

Another problem is that most 3-chip CCD cameras use ultra-precision dichroic filter layers on the prism surfaces to separate the light into its red, green and blue components. Video lenses have to specially optimized to avoid weird phase effects that can compromize colour quality, and this tends to impact on their resolution capability. Generally, TV lenses don't make terribly good film lenses and vice versa. (Unless you're talking about single-chip cameras, which is what the Genesis etc are all about)
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#6 Sir Alvin Ekarma

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Posted 15 July 2006 - 10:46 AM

Thanks for the info!
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