Note: The RedCat was upgraded in late 2019 with exciting new features! In a nutshell:
The new RedCat 51 is the answer for those seeking a very highly corrected lens in the common telephoto focal length range. Today's capable camera sensors don't quite demand the kinds of fast f/ratios in vogue in the past. This permits to design a highly optimized system possessing of high resolving power, well controlled aberrations, a large, flat focal surface, in a light-weight package, all at an attractive price.
The FPL-53 substrate used in its objective has dispersion characteristics not much different from that of the much vaunted fluorite crystal, and so is termed a synthetic fluorite. This permits the employment of a fairly fast f/4.9 while delivering superb chromatic aberration suppression.
Don't let the seemingly small element count of just four lenses put you off. The Petzval configuration contributes to the flat field over the considerable image circle of 44mm. And the uniformity of spot sizes and hence resolving power from on axis out to the edge of that field is remarkable.
The familiar helical focus scheme common to so many camera lenses is adopted. A focus tension adjustment ring permits to set the focus action to the desired degree of 'tightness.' Filter wheels can be accommodated, or 48mm filters can be installed inside the removable 48mm mounting ring.
The field rotator ring allows to orient the camera to any desired angle for framing of your target. A scale graduated in degrees at the rear of the lens body permits precise setting. The mounting dovetail bar is reversible, depending on whether your mount supports the Vixen or Arca-Swiss system.
To aid in setting precise focus, a patented Bhatinov mask is provided. For quick setting based on the instrument configuration, the lens barrel has a printed, calibrated scale in millimeters, with vernier for a more precise initial setting.
The lens body at the rear has an M48 thread. Instrument configurations requiring longer back focus, such as filter wheels, can be attached directly.