The William Optics RedCat 51 II refractor telescope features a 51mm objective lens in a sleek quadruplet Petzval APO design, using Synthetic Fluoride (FPL53 and FPL51) glass for a full frame flat field image.
The William Optics RedCat 51 II has received updates from the original RedCat 51 including a revamp for finer focus control via the dewshield tension control adjustment. This internal focusing mechanism keeps the dewshield stationary as you change focus (no more snagged or twisted cables or dew heating strips). The helical focuser mechanism has also been improved.
Inspired by luxury watches, the field rotator is fully rotatable by 360 degrees and is laser etched with a degree indicator rotator marked to a precision of one degree. Focusing is similar to a telephoto camera lens with a smooth helical style focuser which has an attractive finish and engraved calibration markings, and it includes a tension adjustment to increase focusing drag or to lock the focuser in place for fast and accurate focusing. To ensure that you will have the most precise framing possible in a small portable system, the camera can be rotated to with accuracy.
Just after the field rotator, is a slot for a 48mm threaded astronomy filter. The back of the telescope also includes M48x0.75 threads to attach a Micro-4/3, Nikon, Canon, Sony, or Pentax camera with a 48mm wide T-ring (sold separately). This is truly a telescope built for imagers.
The RedCat 51 optical tube is held with a single ring that’s sufficiently rigid to hold the tube and a large DSLR without flexure. You can easily rotate the tube with the help of a large locking knob. The tube ring also includes female threads that let you add a red-dot finder, guide camera, microphone rig, or other accessories.
The William Optics RedCat 51 also comes with a range of useful accessories with astronomy imaging in mind. There’s a super-bright Bahtinov mask that makes it a snap to focus the telescope in just a few seconds. Cap the mask with the ‘whiskered cat’ cover, and it serves as a protective cap for the objective lens.
The William Optics RedCat 51 II also comes with a reversible mounting base for Vixen-style astronomy mounts or an Arca-Swiss mount used in photography tripod heads. A sun-shade/dew-shield keeps stray light out of the telescope, and you can invert the shield and slide it over the objective cell to minimize the length of the tube for transport and storage. And all this is packed into a portable size. The tube is just 228mm x 80mm (9″ x 3.1″) with the retracted dew shield, and it weighs just 1.3kg (2.9 lbs) offered in an attractive anodized aluminum alloy premium red/black finish.
Included with the RedCat 51 is a convenient soft carry case, removeable dew shield, M48 camera adapter, and William Optics patented Bahtinov mask cap. The William Optics RedCat 51 Petzval telescope is ideally suited to night sky astrophotography, wide field astroimaging and wildlife photography.
True Fluorite is a rare mineral which create very expensive optical lenses. Being a natural material, consistency and impurities are additional factors which further increases cost as does the cost of mining and the impact on our environment. The synthetic fluorite glass used in the William Optics RedCat 51 II is a highly stable monocrystal completely free of impurities. It does not emit fluorescence in UV light and is an extraordinarily clear lens material. Great care is taken during manufacturing for grinding and polishing this material to ensure that the lens does not chip or scar, and the result is a lens that is completely free of chromatic aberration.
The William Optics RedCat 51 II ideal for ultra-wide-field imaging of the deep sky and for terrestrial imaging of birds, landscapes, and wildlife. The RedCat 51 focal length is 250mm, which many find to be a sweet spot for wide field astrophotography. The Orion Nebula, Andromeda Galaxy, Heart and Soul Nebulae, North America Nebula, and many more popular regions of the sky easily fit into the field of view. With premium apochromatic optics in a Petzval design, the RedCat 51 is sharper and better corrected than many brand-name camera lenses of similar focal length. The superb optical design and a fast focal ratio of f/4.9 make this little scope a powerful imaging tool.
With its high-quality synthetic fluorite FPL53 and FPL51 glass in a 4-element, 3-group classic Petzval design users will receive superb color correction and an exceptionally flat field. No field flattener is needed with this scope. The RedCat is engineered to have a big 43mm image circle compatible with APS-C and full-frame DSLRs, mirrorless, and dedicated astronomy cameras. With a camera with a full-frame (36mm x 24mm) sensor, the telescope offers an expansive field of view nearly 10 degrees across the sensor diagonal.
The RedCat 51 is optimized for use as an imaging instrument, but it also makes a superb little scope for visual use. Just add William Optics’ optional 1.25″ erecting prism diagonal made specifically for this scope (sold separately) and your favorite eyepiece, and you’re ready for a night of observing the Milky Way or for a pleasant day of birdwatching. The helical focuser has an attractive finish and engraved calibration markings, and it includes a tension adjustment to increase focusing drag or to lock the focuser in place.
The lens assembly can be moved within the telescope body over 33mm by rotating the focusing collar in the front. The distance from the base of the M48 male thread on the RedCat to the chip plane should be 59.7mm with the lens cell completely retracted at the 0mm position. With the lens cell fully extended to 33mm, the chip-to-thread distance must at least be 59.7 – 33 = 26.7mm. This means the thread-to-chip distance can be anywhere between 26.7mm and 59.7mm to reach focus. This is easily achieved with DSLRs with standard M48 T-rings. Many astroimaging cameras will also reach focus with a standard 2″ M48 threaded nosepiece or with accessories such as filter wheels.
The William Optics RedCat 51 II specifications include:
– Focal Length: 250mm
– Diameter: 51mm
– Aperture: f/4.9
– Focuser: Helical focuser
– Image Circle: >43mm
– Tube length (fully retracted): 228mm
– Tube length (fully extended): 291mm
– Dew Shield Circumference: 255mm
– Dew Shield Diameter: 80mm
– Weight: 2.9 lbs / 1.3kg (OTA only); 3.9 lbs / 1.76 kg (OTA with ring and dovetail)
– Interchangeable T-mounts (sold separately): Canon EF, Nikon F, Sony E, Pentax, Micro Four Thirds, Fuji.
You can learn more about the William Optics RedCat 51 II here.
And to make it easier for you to get the most extensive news, articles and reviews that are only available in the magazine pages of Astronomy Technology Today, we are offering a 1 year magazine subscription for only $6! Or, for an even better deal, we are offering 2 years for only $9. Click here to get these deals which only will be available for a very limited time. You can also check out a free sample issue here.