This is the latest II-U (MK2.5) version.

Designed to be the best, affordable, small, lightweight and fast Apochromatic refactor for astrophotography. The unique optical design includes the highest quality glass for the best possible color correction and flat large image circle suitable for full frame sensors. The result is a 51 mm objective lens, in a sleek Petzval design, delivering outstanding images with unbeaten portability.

Australian Authorised dealer

Mount a ZWO EAF Electronic focuser & an ASIAIR PRO to the RedCat 51 using the Black Cat Mount. 

The William Optics RedCat 51 APO II is a 51mm f/4.9 Petzval refractor that features synthetic fluoride (FPL53 and FPL51) glass elements for a full frame, flat field image.

Provides high resolution images when used for astrophotography or wildlife photography.

It's fast f/4.9 focal ratio and compact size makes it ideal for convenient wide field astrophotography or piggybacking. 

Incorporates a smooth helical focuser, a field rotator graduated by degree, a slot for 48mm filters and a reversible dovetail for either Vixen style or Arca-Swiss mounting.