MegaVision’s computer controlled aperture function, AutoStop™, allows the rapid, consistent adjustment of exposure in 1/10 stop increments. Although this might normally be considered an extravagance, this feature has merit for high volume environments. The lenses are also especially convenient for shots that require extensive shades, cutters, or filtration, on or about the lens. Most of you are familiar with craning your neck, flashlight in hand, trying to see the aperture scale on a recessed board, amidst a compendium shade and a cutter on a C-arm... Although this may not be your standard fare, you can easily appreciate the value of an aperture that automatically moves to the optimum aperture you’ve preset without physically touching the lens. The AutoStop™ function is a labor saving device; when you click Focus, it opens to the optimum viewing aperture, and it stops down automatically to the predetermined shooting aperture when you click Capture.
Several lenses are available. Choose from the following list:
28mm f4
60mm f4
80mm f4.5
90mm f4.5
47mm f5.6
80mm Macro f5.6
100mm f5.6
120mm f5.6
120mm Macro f5.6
135mm f5.6
150mm f5.6
Although the lenses advertise one-tenth stop accuracy, in practical use they can achieve finer gradations of exposure. AutoStop™ lenses are really nothing more than electrically operated mechanisms that “automatically” move the same lever you’re used to manipulating for aperture changes. Like any aperture they suffer from hysteresis, the mechanical inability (which translates to inaccuracy) of the lever to make exactly the same scale indicated aperture when set from the wide open side of the scale (f/5.6) as compared with making the same scale indicated aperture when pulled from the f/45 side of the scale. The mechanical tolerance in the lever and aperture blade mechanism is responsible for this inaccuracy and the tolerance (and subsequent inaccuracy) increases with the amount of use, or wear, the aperture mechanism has endured. This is why we’re taught to set our apertures starting from one side of the scale only. Choosing to ignore this imperative will lead to apertures different from the indicated aperture, which is how we can achieve apertures between the indicated one-tenth markings. Take the aperture a tenth or two past the aperture you’re looking to modify and bring it back the “wrong” way to get that intermediate aperture. Use Color Coded Light Metering to verify the proper aperture setting.
One other important thing to remember. So far, all of the AutoStop™ lenses use the Copal (and Compur) number 0 (zero) size. If for some reason the AutoStop™ mechanism, AutoStop™ cable, or Omega board develop a problem, you may unscrew the lens doublet (front & back) from the aperture mechanism and you can then mount the glass into any ordinary number 0 shutter (be very careful; if the AutoStop™ lens has a thin, brass shim between the rear element and the aperture mechanism, be sure to keep track of it). This will allow you to use the AutoStop™ glass even if the aperture mechanism has gone on vacation.
Choose the AutoStop™ focal length as you would any lens. If you are interested in an AutoStop™ lens, compare the focal length you’re interested in with at least 2 other focal lengths, one slightly longer and one slightly wider. Compare sharpness, working distance, and coverage (for swings and tilts). We recommend apochromatic formulas above non-apochromatic formulas. They’re a little more expensive but well worth the extra cost in the long run.
Since the T2 chip is physically close in size to the 35mm format, consider the lens you’d use if you were shooting 35mm. If for instance, you need a moderate wide angle you’ll need something in the 35mm range. True wide angle will need something starting at 28mm and go wider. Telephoto starts around 105mm and gets longer. You know the drill, let your experience be your guide when considering which focal length you’ll need.