Manufacturer: William Optics
Price: $1598
William Optics RedCat 61 Apochromatic Petzval Refractor
William Optics has done it again. Following up its wildly popular RedCat 51 and RedCat 71, the company has released its new RedCat 61. The latest version comes with some new enhancements including its novel patented internal focusing mechanism.
This scope features a new focus design that solves the loss of focus issue common with many of the heavier state-of-the-art imaging gear setups. By migrating the focuser movement into the inside of the optical tube, a great deal of stability is achieved, making the loss of focus due to camera weight much less likely. If you study the optical tube during active focusing, you will not see movement of the focuser portion of the tube. As with most high-quality refractors, the RedCat 61 features a two-speed focuser which makes perfect focus easily achievable.
Key Features:
Optics: An apochromatic quadruplet objective lens system is designed to minimize chromatic aberration. Most importantly for astrophotographers, the Petzval design results in a full-frame flat field without the need for an additional field flattener. Those who have used optional field flatteners know that getting the back focus precisely right is necessary to achieve the best flat field. This is easier said than done!
Focal Ratio: The telescope has a 61mm (2.4 inches) aperture and a focal length of 300mm, providing a fast focal ratio of f/4.9. The focal length sits right between that of the RedCat 51 and the RedCat 71, resulting in a nice wide field compromise between these two scopes. This wide field of view is great for imaging large nebula, galaxies and even portions of the Milky Way.
Portability: The RedCat 61 is perfect for photographers who like to travel to dark sites to do their imaging. Its compact size makes it compatible with many modern imaging set-ups. The unique focusing mechanism makes it possible to have heavier imaging equipment attached than its closest competitors.
Focuser: The dual-speed rack and pinion focuser is smooth and has no shift of the image while focusing. Of course, the fine adjustment knob is great for getting perfect focus and is compatible with several of the common auto-focusers on the market including the ZWO EAF (see my review).
Vixen-style dovetail: Many modern mounts allow this connection.
Accessories: The integrated handle makes carrying the scope easy, and the lens cap has an integrated Bahtinov mask.
Construction: Like all William Optics gear, The RedCat 61 is not only high-quality, it is also attractive. The red anodized construction is both sturdy and lightweight.
RedCat specs comparison
| Redcat 51 | Redcat 61 | Redcat 71 | |
| Focal Length | 250mm | 300mm | 348mm |
| Aperture | 51mm | 61mm | 71mm |
| Focal Ratio | f/4.9 | f/4.9 | f/4.9 |
| Optical Design | Petzval | Petzval | Petzval |
| Image Circle | >43 | 46mm | >43mm |
| Tube Length | 291mm | 365mm | 435mm |
| OTA Weight | 2.9 lbs / 1.3kg | 5.43lbs / 2.465kg | 6.2lbs / 2.8kg |
| Total Weight | 3.9 lbs / 1.76 kg (OTA with ring and dovetail) | 7.47lbs / 3.390kg (OTA with ring, dovetail and saddle) | 8.2lbs / 3.7kg (OTA with ring, dovetail and saddle) |
| Price | $865 | $1598 | $1698 |
Verdict
The apochromatic Petzval optical design is perfect for creating round stars across the entire full-frame image circle without chromatic aberration. The brand-new internal focusing design makes the RedCat 61 a great pick for anyone wanting a high-quality refractor, and it opens the door to an even wider selection of imaging accessories without the worry about excessive weight bending the image path.