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Optics

If you are the type of shooter who likes to brag about your “fully digital camera”, you might want to tone down that boast just a notch. You see, one of the most important parts of any camera system has always been analog and looks to remain that way for the immediate future.

Of course we are talking about the lens. Yes, the mighty digital juggernaut doesn’t seem to stand a chance of beating common, ordinary glass.

OK. So maybe it’s not dime store paperweight type stuff that we are talking about here. No, certainly not when the discussion progresses to high definition camera lenses. Teams of engineers at companies like Fujinon and Canon toil on in an attempt to make sure that their glass is capable of delivering all of the wavelengths of visible light to the camera imagers whether they be ccds, cmos pickups or some new hush-hush type technology. This task is not just daunting; it is impossible according to the laws of physics. They toil on anyway!

Lens techies use the term MTF to try to describe lens performance. MTF stands for Modulation Transfer Function. MTF is a slick way of defining how good any given lens is at doing its job. That job involves delivering the maximum optical bandwidth to the imaging devices no matter what flavor of technology they may be.

That bandwidth is made up of wavelengths of light in the visible spectrum. Those wavelengths cover all of the colors from the warm end to the cool end of the spectrum. MTF is however, a bit of a moving target. MTF of all lenses changes with things like aperture, focal length, object distance, and distance from the center of the imaging plane.

The dynamic interplay of these factors and others can lead to a number of “aberrations”. Aberrations are bad things especially when it comes to camera optics. One family of aberrations that lens manufacturers work hard to avoid is that of chromatic aberrations. A chromatic aberration would occur when the camera sees a particular wavelength of light an a different way than the human eye sees that same wavelength of light (also known as a color!)

Lenses that you might spot on any given eng/efp style camera could range anywhere from a standard definition video style lens to a true, film style prime lens. Video lenses tend to be of the zoom variety where you can alter the focal length, but primes are of a fixed focal length. The only control that you can exercise over those lenses is aperture and focus control. Two categories of lenses that fall between standard definition video lenses and true primes are high definition video (zoom) lenses and cine style primes.

Lens manufacturers have much higher standards for the design and production of high definition video lenses than they do for the design and production of standard definition video lenses. One example of this is that the optical bandwidth requirement of an HDTV lens is 2.7 times that of a standard definition lens! You cannot possibly do justice to a high definition camera by equipping it with a standard definition lens. Happily, the inverse is true. You can make a dramatic improvement in the quality of standard definition video by equipping a standard def camera with a high def lens. Cine style primes are an attempt to bridge the gap between the high definition zooms and the true film primes.

Looking forward, it is fair to assume that the field of “digital cinematography” will blossom.
This will give all of the folks who know about f-stops a chance to learn about t- numbers and vice versa. If you are one of those folks, Broadcast Rentals stands ready to assist you with your creative journey.