William Optics RedCat 51 III WIFD f/4.9 Petzval Refractor Telescope
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Introducing the RedCat 51 Gen III: The Latest Evolution of Best-Selling RedCat Series
The RedCat 51 Gen III is an apochromatic refractor that delivers stunning, crystal-clear images. With anti-reflective lens coatings and high-quality Petzval optics, it offers pinpoint stars across the entire field and reduces chromatic aberration. Chromatic aberration is when colors appear distorted in your images. It happens because different colors of light bend differently through the lenses of a refractor. This causes colors to focus at different points, making bright objects like stars appear with purple or blue halos around them.
The Gen 3 improves on what made the original RedCat great! It has the new William Optics Internal Focus Design (WIFD). This design works perfectly with electronic focusers like the ZWO EAF. By integrating the focuser inside the optical tube, the WIFD eliminates any need for an external drawtube. This reduces the chance of tilt, sag, and mechanical flexure, which means greater stability and sharper images.
The Gen III RedCat 51 has an updated tilt adapter with M54 threads to reduce vignetting on full-frame cameras. It also comes with an M48 x 0.75 adapter for standard setups. With a fast f/4.9 focal ratio and 250mm focal length, the RedCat 51 Gen III is perfect for wide-field shots of deep-space objects. If you're upgrading from a camera lens, new to astrophotography, or looking for a portable telescope, the RedCat 51 WIFD is a fantastic choice!
Key Features of the RedCat 51 WIFD Gen 3
- 4-Element Petzval Optics: The RedCat 51 III features a 4-element Petzval design. This provides ultra-sharp, color-free images with minimal distortion. Stars stay sharp across the entire field, including the edges, so you get stunning images every time!
- Short Focal Length: With a focal length of 250mm and a large image, the RedCat 51 III excels in wide-field astrophotography.
- Fast Focal Ratio: A fast focal ratio of f/4.9 means the RedCat 51 III gathers light quickly. So you can capture bright, detailed images in less time!
- Internal Focus System (WIFD): The internal focus system provides smooth, precise adjustments without the telescope body extending.
- Premium Glass: The RedCat 51 III uses FPL-53 glass, a top-tier material that provides excellent light transmission. It also minimizes chromatic aberration (color fringing).
- Easy Framing: The built-in field rotator with markings makes framing a breeze!
- Built-In Filter Thread: The RedCat’s built-in 48mm filter thread gives you the flexibility to use standard 2" filters without a filter wheel or drawer.
- Full-Frame & APS-C Compatible: Whether you're using a full-frame or APS-C camera, the RedCat 51 III works flawlessly with both thanks to its 45mm image circle.
RedCat 51 Refractor Telescope: Cutting-Edge Design for Stunning Wide-Field Astrophotography
Revolutionary WIFD Focuser: A New Era in Precision Focus
Earlier versions of the RedCat 51 used a helical-style focuser, similar to a camera lens. It had a rubber grip that wasn’t ideal for autofocus systems. With the RedCat 51 Gen III, William Optics took user feedback into account and introduced the William Optics Internal Focus Design (WIFD). One of the most advanced focusing systems available in consumer telescopes today!
Unlike traditional focusers that extend out the back of the telescope, WIFD moves the optical elements inside the tube. This eliminates vignetting, prevents sensor tilt from the telescope itself, and provides rock-solid stability. With no external drawtube, there’s no risk of sag, even when using heavy accessories like a large filter wheel or DSLR camera. To ensure even greater precision, William Optics includes a built-in tilt adapter to correct any misalignment caused by other components in the imaging train.
Premium Optics & Petzval Design for Next-Level Imaging
The RedCat 51 III features four lens elements arranged in a Petzval optical design with high-quality FPL-53 glass, ensuring excellent color correction and a flat field across a 45mm image circle. This design ensures exceptional image sharpness across the entire field of view by addressing issues like field curvature and chromatic aberration. This is a huge benefit for astrophotography, where sharp, clear images help reveal more detail in nebulae and galaxies.
The Petzval design eliminates the need for a separate field flattener, which is required in other refractor telescopes to ensure round stars across the entire image. Removing this component saves on cost, complexity, and total system weight.
With this design, you also remove the need for specific backfocus calculations. With a traditional refractor and field flattener, there is often a fixed back-focus distance, typically 55 millimeters. But with the RedCat 51 WIFD, you can achieve focus using any imaging system that is 68.2 millimeters or less from the M54 threads on the back of the scope. This means you can easily add accessories like cameras, rotators, or filter wheels, and seamlessly adjust focus without worrying about rigid back-focus standards.
The William Optics RedCat 51 Gen III WIFD includes everything needed for high-quality results, making it both simpler to use and more cost-effective!
Designed for Wide-Field Astrophotography
The 250mm focal length and f/4.9 focal ratio of the RedCat 51 make it an ideal choice for wide-field astrophotography, allowing you to capture expansive views of nebulae, galaxy clusters, and large open star fields.
The RedCat is great for beginners who may be using portable tracking mounts like the Sky-Watcher Star Adventurer GTi, Star Adventurer 2i Pro, or iOptron SkyGuider. Because of its wide field of view, minor imperfections and distortions in star shape are less noticeable. This means you don’t need to track the night sky as precisely as you would if you were using longer focal lengths.
The combination of a fast f/4.9 aperture and short focal length allows the telescope to gather light quickly! For instance, an image that would take 4 hours at f/8 can be captured in just 2 hours at f/4.9. This is a significant time-saver when photographing faint objects. It’s especially valuable when you're working with limited clear skies or light pollution, allowing you to capture detailed images faster.
The RedCat 51 Gen III WIFD accommodates high-resolution cameras and heavier, cooled setups with ease, offering a versatile imaging experience with a design that ensures minimal vignetting on full-frame sensors.
Explore More Key Advantages for Stellar Astrophotography
Seamless Compatibility: Works with ZWO EAF Right Out of the Box
The RedCat 51 WIFD arrives fully compatible with the ZWO EAF (electronic automatic focuser). Unlike previous models that required third-party adapters, this version makes it easier than ever to achieve perfect focus.
Best of all, installation is quick and hassle-free, saving you time, effort, and frustration. Here’s how:
- Remove the lock and tension screw from the focuser.
- On the focus knob without the fine adjustment, use a 2mm Allen key to remove the top screw.
Rotate the knob to locate two inner shaft screws inside the hole. Loosen these, but do not remove them completely. - Remove the focus knob.
- Align the EAF’s mounting bracket with the exposed screw hole and the nearby 2mm hole on the fine-tuning knob end, near where the lock and tension screw was removed.
- Align the EAF’s mounting bracket with the exposed screw hole and the 2mm hole on the fine-tune knob end (near where the lock and tension screw was).
- Use the two inner shaft screws to secure the EAF to the focuser shaft.
- Tighten both bracket screws to finish the installation.
Download instructions for installing the EAF onto the RedCat 51 III.
Easy Filter Integration: Built-In Filter Thread
Just like earlier RedCat 51 models, the RedCat 51 WIFD keeps things simple by including a built-in 2" filter thread. This means you don’t need any extra accessories or adapters to start using your favorite filters.
This is especially handy for DSLR or mirrorless users—no need for clip-in filters. Just use any standard 2" filter across all your cameras, whether it's a dedicated astronomy camera or a regular digital camera.
Installing your filter is easy! Unscrew the included M48 adapter, thread in any standard M48 light pollution or specialty filter, and you’re ready to go.
This is especially helpful if you're shooting from a city or suburban area where city lights can wash out faint deep-sky targets. Using filters helps improve contrast and bring out more detail in your images, even under light-polluted skies.
Take it Anywhere: Lightweight & Travel-Friendly
Weighing just 3.9 lbs (1.77 kg), the RedCat 51 is easy to carry, easy to mount, and quick to set up.
Its compact size also makes it ideal for beginners who don’t want to deal with bulky gear, and it’s just as appreciated by seasoned imagers looking for a grab-and-go telescope that delivers serious results.
Less weight also means less strain on your mount, which helps improve stability and tracking accuracy for sharper images.
Included Tilt Adapter for Better Imaging
The new RedCat 51 features an upgraded tilt adapter with M54 threads, offering improved performance for full-frame sensors and potentially reducing vignetting.
This is a significant upgrade over the previous version. Plus, a standard M48 x 0.75 adapter is included, making it compatible with common imaging trains for even more flexibility.
Durable Construction for All-Night Sessions
The RedCat 51 is built to last. It features a solid aluminum housing that’s engineered to withstand the rigors of outdoor use. Whether you’re braving chilly nights or dealing with humidity, this telescope can perform in the toughest conditions. Its rugged build ensures that it holds up against the elements, giving you peace of mind during long nights of astrophotography.
Ready for Visual Use: Compatible with 1.25” Eyepieces
William Optics offers a 1.25" 90-degree diagonal (sold separately), allowing you to use the RedCat 51 with eyepieces for visual observing as well.
Keep in mind that, depending on the back-focus requirements of your eyepiece, not all 1.25" eyepieces may reach focus. Also, this scope is not compatible with 2" diagonals or eyepieces.
Easily Connect Your Camera
The RedCat 51 Gen III WIFD works with a wide range of cameras, so you can build the setup that fits you best. It includes M54 x 0.75 and M48 x 0.75 threads for direct connection to most astronomy cameras and accessories.
If you’re using a DSLR or mirrorless camera, just add a T-ring or T-mount for your camera brand, and you’re ready to go. Whether you shoot with a full-frame, APS-C, or dedicated astro camera, the RedCat 51 gives you the flexibility to start imaging right away.
All the Essentials Included
The William Optics RedCat 51 Gen III comes fully equipped, so you can start imaging right away!
You’ll get a Bahtinov mask for quick and accurate focusing. The dual Vixen/Arca-Swiss mounting plate makes it easy to attach the telescope to your mount or many standard photo tripods. Plus, it includes a soft carry case, handlebar, lens cap, and a full Allen key set for quick adjustments.
This saves you both time and money. You won’t need to hunt down extra parts. Just add your camera and mount, and you’re ready to capture the night sky!
RedCat 51 III Component Diagram
A. Rear Dust Cap (M48)
B. Saddle Handle Bar
C. WIFD Focuser
D. Dew Shield
E. Lens Cover with Bahtinov Mask
F. Front Bahtinov Mask Cover
G. Mounting Ring / Knob
H. Camera Angle Rotator
I. 210mm Dovetail Bar
J. Dual Speed 10:1 Ratio Focus Knob with Fine Focus Control
K. M4 Screw Holes for Finder Bracket
L. M4 Locking Screws on Saddle Handle Bar
M. Camera Angle Rotation Locking Screw
N. M4 Screw Holes for Finder Bracket
O. Focuser Adjusting Knob with Thermometer
P. M48 Adapter (for Camera Mount)
Specifications
- Optical Design: Petzval (4-element)
- Glass Type: FPL-53
- Focal Length: 250mm
- Aperture: 51mm
- Focal Ratio: f/4.9
- Image Circle: 48mm (full frame)
- Focuser: William Optics Internal Focus Design (WIFD)
- Focuser Compatibility: ZWO EAF
- Focus Travel: 0 - 23mm (Ruler to 30mm)
- Adapter Included: Tilt adjuster, Rotator, M54 to M48 adapter
- Optional Flattener: No flattener required
- Camera Format: Full frame, APS-C, M4/3
- Tube Length: 346mm - 298mm
- Dew Shield Circumference: 265mm
- Dew Shield Diameter: 84mm
- Weight of OTA only: 3.90 lbs (1.77 kg)
- Weight of OTA with tube rings, dovetail, & saddle: 5.25 lbs (2.38 kg)
- Soft Carrying Case External Dimensions: 39cm x 25cm x 27cm
| Free Shipping Graphic | Free Contiguous US Shipping |
|---|---|
| Telescope Focal Length | Up to 300mm |
| Hide Found a better Shipped Price on Frontend? | No |
- RedCat 51 WIFD
- Soft Carry Case
- Duel Mounting Plate
- Tube rings & Handlebar
- Bahtinov Mask Cap
- Allen Key Set
- Lens Cap
Introducing the RedCat 51 Gen III: The Latest Evolution of Best-Selling RedCat Series
The RedCat 51 Gen III is an apochromatic refractor that delivers stunning, crystal-clear images. With anti-reflective lens coatings and high-quality Petzval optics, it offers pinpoint stars across the entire field and reduces chromatic aberration. Chromatic aberration is when colors appear distorted in your images. It happens because different colors of light bend differently through the lenses of a refractor. This causes colors to focus at different points, making bright objects like stars appear with purple or blue halos around them.
The Gen 3 improves on what made the original RedCat great! It has the new William Optics Internal Focus Design (WIFD). This design works perfectly with electronic focusers like the ZWO EAF. By integrating the focuser inside the optical tube, the WIFD eliminates any need for an external drawtube. This reduces the chance of tilt, sag, and mechanical flexure, which means greater stability and sharper images.
The Gen III RedCat 51 has an updated tilt adapter with M54 threads to reduce vignetting on full-frame cameras. It also comes with an M48 x 0.75 adapter for standard setups. With a fast f/4.9 focal ratio and 250mm focal length, the RedCat 51 Gen III is perfect for wide-field shots of deep-space objects. If you're upgrading from a camera lens, new to astrophotography, or looking for a portable telescope, the RedCat 51 WIFD is a fantastic choice!
Key Features of the RedCat 51 WIFD Gen 3
- 4-Element Petzval Optics: The RedCat 51 III features a 4-element Petzval design. This provides ultra-sharp, color-free images with minimal distortion. Stars stay sharp across the entire field, including the edges, so you get stunning images every time!
- Short Focal Length: With a focal length of 250mm and a large image, the RedCat 51 III excels in wide-field astrophotography.
- Fast Focal Ratio: A fast focal ratio of f/4.9 means the RedCat 51 III gathers light quickly. So you can capture bright, detailed images in less time!
- Internal Focus System (WIFD): The internal focus system provides smooth, precise adjustments without the telescope body extending.
- Premium Glass: The RedCat 51 III uses FPL-53 glass, a top-tier material that provides excellent light transmission. It also minimizes chromatic aberration (color fringing).
- Easy Framing: The built-in field rotator with markings makes framing a breeze!
- Built-In Filter Thread: The RedCat’s built-in 48mm filter thread gives you the flexibility to use standard 2" filters without a filter wheel or drawer.
- Full-Frame & APS-C Compatible: Whether you're using a full-frame or APS-C camera, the RedCat 51 III works flawlessly with both thanks to its 45mm image circle.
RedCat 51 Refractor Telescope: Cutting-Edge Design for Stunning Wide-Field Astrophotography
Revolutionary WIFD Focuser: A New Era in Precision Focus
Earlier versions of the RedCat 51 used a helical-style focuser, similar to a camera lens. It had a rubber grip that wasn’t ideal for autofocus systems. With the RedCat 51 Gen III, William Optics took user feedback into account and introduced the William Optics Internal Focus Design (WIFD). One of the most advanced focusing systems available in consumer telescopes today!
Unlike traditional focusers that extend out the back of the telescope, WIFD moves the optical elements inside the tube. This eliminates vignetting, prevents sensor tilt from the telescope itself, and provides rock-solid stability. With no external drawtube, there’s no risk of sag, even when using heavy accessories like a large filter wheel or DSLR camera. To ensure even greater precision, William Optics includes a built-in tilt adapter to correct any misalignment caused by other components in the imaging train.
Premium Optics & Petzval Design for Next-Level Imaging
The RedCat 51 III features four lens elements arranged in a Petzval optical design with high-quality FPL-53 glass, ensuring excellent color correction and a flat field across a 45mm image circle. This design ensures exceptional image sharpness across the entire field of view by addressing issues like field curvature and chromatic aberration. This is a huge benefit for astrophotography, where sharp, clear images help reveal more detail in nebulae and galaxies.
The Petzval design eliminates the need for a separate field flattener, which is required in other refractor telescopes to ensure round stars across the entire image. Removing this component saves on cost, complexity, and total system weight.
With this design, you also remove the need for specific backfocus calculations. With a traditional refractor and field flattener, there is often a fixed back-focus distance, typically 55 millimeters. But with the RedCat 51 WIFD, you can achieve focus using any imaging system that is 68.2 millimeters or less from the M54 threads on the back of the scope. This means you can easily add accessories like cameras, rotators, or filter wheels, and seamlessly adjust focus without worrying about rigid back-focus standards.
The William Optics RedCat 51 Gen III WIFD includes everything needed for high-quality results, making it both simpler to use and more cost-effective!
Designed for Wide-Field Astrophotography
The 250mm focal length and f/4.9 focal ratio of the RedCat 51 make it an ideal choice for wide-field astrophotography, allowing you to capture expansive views of nebulae, galaxy clusters, and large open star fields.
The RedCat is great for beginners who may be using portable tracking mounts like the Sky-Watcher Star Adventurer GTi, Star Adventurer 2i Pro, or iOptron SkyGuider. Because of its wide field of view, minor imperfections and distortions in star shape are less noticeable. This means you don’t need to track the night sky as precisely as you would if you were using longer focal lengths.
The combination of a fast f/4.9 aperture and short focal length allows the telescope to gather light quickly! For instance, an image that would take 4 hours at f/8 can be captured in just 2 hours at f/4.9. This is a significant time-saver when photographing faint objects. It’s especially valuable when you're working with limited clear skies or light pollution, allowing you to capture detailed images faster.
The RedCat 51 Gen III WIFD accommodates high-resolution cameras and heavier, cooled setups with ease, offering a versatile imaging experience with a design that ensures minimal vignetting on full-frame sensors.
Explore More Key Advantages for Stellar Astrophotography
Seamless Compatibility: Works with ZWO EAF Right Out of the Box
The RedCat 51 WIFD arrives fully compatible with the ZWO EAF (electronic automatic focuser). Unlike previous models that required third-party adapters, this version makes it easier than ever to achieve perfect focus.
Best of all, installation is quick and hassle-free, saving you time, effort, and frustration. Here’s how:
- Remove the lock and tension screw from the focuser.
- On the focus knob without the fine adjustment, use a 2mm Allen key to remove the top screw.
Rotate the knob to locate two inner shaft screws inside the hole. Loosen these, but do not remove them completely. - Remove the focus knob.
- Align the EAF’s mounting bracket with the exposed screw hole and the nearby 2mm hole on the fine-tuning knob end, near where the lock and tension screw was removed.
- Align the EAF’s mounting bracket with the exposed screw hole and the 2mm hole on the fine-tune knob end (near where the lock and tension screw was).
- Use the two inner shaft screws to secure the EAF to the focuser shaft.
- Tighten both bracket screws to finish the installation.
Download instructions for installing the EAF onto the RedCat 51 III.
Easy Filter Integration: Built-In Filter Thread
Just like earlier RedCat 51 models, the RedCat 51 WIFD keeps things simple by including a built-in 2" filter thread. This means you don’t need any extra accessories or adapters to start using your favorite filters.
This is especially handy for DSLR or mirrorless users—no need for clip-in filters. Just use any standard 2" filter across all your cameras, whether it's a dedicated astronomy camera or a regular digital camera.
Installing your filter is easy! Unscrew the included M48 adapter, thread in any standard M48 light pollution or specialty filter, and you’re ready to go.
This is especially helpful if you're shooting from a city or suburban area where city lights can wash out faint deep-sky targets. Using filters helps improve contrast and bring out more detail in your images, even under light-polluted skies.
Take it Anywhere: Lightweight & Travel-Friendly
Weighing just 3.9 lbs (1.77 kg), the RedCat 51 is easy to carry, easy to mount, and quick to set up.
Its compact size also makes it ideal for beginners who don’t want to deal with bulky gear, and it’s just as appreciated by seasoned imagers looking for a grab-and-go telescope that delivers serious results.
Less weight also means less strain on your mount, which helps improve stability and tracking accuracy for sharper images.
Included Tilt Adapter for Better Imaging
The new RedCat 51 features an upgraded tilt adapter with M54 threads, offering improved performance for full-frame sensors and potentially reducing vignetting.
This is a significant upgrade over the previous version. Plus, a standard M48 x 0.75 adapter is included, making it compatible with common imaging trains for even more flexibility.
Durable Construction for All-Night Sessions
The RedCat 51 is built to last. It features a solid aluminum housing that’s engineered to withstand the rigors of outdoor use. Whether you’re braving chilly nights or dealing with humidity, this telescope can perform in the toughest conditions. Its rugged build ensures that it holds up against the elements, giving you peace of mind during long nights of astrophotography.
Ready for Visual Use: Compatible with 1.25” Eyepieces
William Optics offers a 1.25" 90-degree diagonal (sold separately), allowing you to use the RedCat 51 with eyepieces for visual observing as well.
Keep in mind that, depending on the back-focus requirements of your eyepiece, not all 1.25" eyepieces may reach focus. Also, this scope is not compatible with 2" diagonals or eyepieces.
Easily Connect Your Camera
The RedCat 51 Gen III WIFD works with a wide range of cameras, so you can build the setup that fits you best. It includes M54 x 0.75 and M48 x 0.75 threads for direct connection to most astronomy cameras and accessories.
If you’re using a DSLR or mirrorless camera, just add a T-ring or T-mount for your camera brand, and you’re ready to go. Whether you shoot with a full-frame, APS-C, or dedicated astro camera, the RedCat 51 gives you the flexibility to start imaging right away.
All the Essentials Included
The William Optics RedCat 51 Gen III comes fully equipped, so you can start imaging right away!
You’ll get a Bahtinov mask for quick and accurate focusing. The dual Vixen/Arca-Swiss mounting plate makes it easy to attach the telescope to your mount or many standard photo tripods. Plus, it includes a soft carry case, handlebar, lens cap, and a full Allen key set for quick adjustments.
This saves you both time and money. You won’t need to hunt down extra parts. Just add your camera and mount, and you’re ready to capture the night sky!
RedCat 51 III Component Diagram
A. Rear Dust Cap (M48)
B. Saddle Handle Bar
C. WIFD Focuser
D. Dew Shield
E. Lens Cover with Bahtinov Mask
F. Front Bahtinov Mask Cover
G. Mounting Ring / Knob
H. Camera Angle Rotator
I. 210mm Dovetail Bar
J. Dual Speed 10:1 Ratio Focus Knob with Fine Focus Control
K. M4 Screw Holes for Finder Bracket
L. M4 Locking Screws on Saddle Handle Bar
M. Camera Angle Rotation Locking Screw
N. M4 Screw Holes for Finder Bracket
O. Focuser Adjusting Knob with Thermometer
P. M48 Adapter (for Camera Mount)
Specifications
- Optical Design: Petzval (4-element)
- Glass Type: FPL-53
- Focal Length: 250mm
- Aperture: 51mm
- Focal Ratio: f/4.9
- Image Circle: 48mm (full frame)
- Focuser: William Optics Internal Focus Design (WIFD)
- Focuser Compatibility: ZWO EAF
- Focus Travel: 0 - 23mm (Ruler to 30mm)
- Adapter Included: Tilt adjuster, Rotator, M54 to M48 adapter
- Optional Flattener: No flattener required
- Camera Format: Full frame, APS-C, M4/3
- Tube Length: 346mm - 298mm
- Dew Shield Circumference: 265mm
- Dew Shield Diameter: 84mm
- Weight of OTA only: 3.90 lbs (1.77 kg)
- Weight of OTA with tube rings, dovetail, & saddle: 5.25 lbs (2.38 kg)
- Soft Carrying Case External Dimensions: 39cm x 25cm x 27cm
| Free Shipping Graphic | Free Contiguous US Shipping |
|---|---|
| Telescope Focal Length | Up to 300mm |
| Hide Found a better Shipped Price on Frontend? | No |
- RedCat 51 WIFD
- Soft Carry Case
- Duel Mounting Plate
- Tube rings & Handlebar
- Bahtinov Mask Cap
- Allen Key Set
- Lens Cap
William Optics RedCat 51 III WIFD f/4.9 Petzval Refractor Telescope # L-RC51RDIII