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RedCat 51

How I Captured the Boogieman Nebula

|Equipment|3 Comments

In this article, I’ll describe how I photographed the Boogieman Nebula (LDN 1622) in the constellation Orion using my camera and telescope. This was the first time I had ever captured this deep-sky object before, and one of only a handful of dark nebulae I have ever photographed. 

LDN 1622 is a dark molecular cloud that is just shy of 10 light-years across in size. The Boogieman Nebula is surrounded by the intense hydrogen gas of Barnard’s Loop and close by to other fascinating deep-sky objects like Messier 78.

In this article, I’ll cover everything from the astrophotography equipment I used to capture the shot, to the image processing techniques I performed to create the final image you see below. My hope is that you can replicate some of my techniques to produce your own image of the Boogieman Nebula to enjoy.

the boogieman nebula

The Boogieman Nebula in Orion. 32 x 4-minutes (2 Hours 8 minutes total)

As most of you know, I take the majority of my deep-sky photos from my backyard at home, but during the new moon phase, I like to escape the city lights and head to a dark-sky site.

This winter has been terrible for astrophotography – night after night of cloudy skies. But in late February, my astronomy weather app (Astrospheric) indicated an upcoming clear patch of sky appearing within the cloud cover.

I crossed my fingers that this forecast would hold true, and booked a one-night stay in a cabin under Bortle 4 skies. Although it was snowing while I set up my telescope, the clouds parted as darkness fell and I was able to enjoy about 4 hours of clear-sky time in total. 

Related Article: The Best Astronomy and Stargazing Apps for your Smartphone


If you would like to follow along and see what the cabin I stayed in looked like, feel free to watch the video below. If you take your astrophotography images in the city like me, I highly recommend searching for dark-sky rentals on Airbnb during the new moon phase.

The Boogieman Nebula

The Boogieman Nebula is a beautiful dark nebula in Orion. Also known as Lynds Dark Nebula (LDN 1622), it is a dark molecular cloud that sits on top of a faint background of hydrogen.

The reflection nebula known as Messier 78 resides nearby, and you may want to consider including this nebula in your image if your field of view is wide enough. 

  • Cataloged: LDN 1622
  • Common Name: The Boogeyman Nebula
  • Constellation: Orion
  • Object Type: Dark Nebula
  • Distance: 500 light-years away

This rather dim object benefits from a dark sky. The Boogieman Nebula (and all dark nebulae) are likely too faint to successfully capture from my backyard in the city.

Nearby M78 is an attractive reflection nebula that glows brightly above Orion’s Belt. At a distance of about 1,500 light-years, this reflection nebula is lit by nearby hot, young stars. The cool blue look of this reflection nebula plays well off of the warmer red regions of hydrogen gas in terms of photographic composition. 

There is plenty of hydrogen gas nearby as well, this region lies next to the massive Barnard’s Loop, which shines in deep red and magenta when photographed with an astro-modified camera.

The main reason I had never photographed the Boogieman Nebula until now is that there are so many other gorgeous deep-sky objects in this region.

I had to restrain myself from capturing the Horsehead Nebula next door for the 12th time. In the image below, you’ll see that the Boogieman Nebula lives north of the bright star in Orion’s Belt known as Alnitak

Boogieman Location

The location of the Boogieman Nebula in Orion. 

From mid-northern latitudes, the best time of year to photograph the Boogieman Nebula is from November to February. From my latitude in Ontario, Canada, LDN 1622 rises to a maximum apparent altitude of about 45 degrees in the sky. 

Due to its proximity to the 3 bright stars in Orion’s Belt, the Boogieman Nebula and M78 are quite easy to find in binoculars or a telescope. Unlike Messier 78 at magnitude 9.5 (which can be seen in a small telescope), the Boogieman Nebula is much too dim to be seen visually through the eyepiece.

Orion constellation map

The location of the Boogieman Nebula and M78 in Orion. 

My Equipment 

I brought my Sky-Watcher EQ6-R Pro telescope mount on this trip. It’s not the most portable telescope mount in the world, but it allows me to mount a small to medium-sized refractor with autoguiding.

This equatorial telescope mount is capable of precise tracking, even using a telescope with a focal length of 1000mm+. The largest telescope I have mounted to the EQ6-R Pro was a William Optics FLT 132 (750mm). 

It can handle a much heavier load than my star tracker, which I also brought along to capture some wide-field images using my Rokinon 135mm F/2 lens. I have yet to take a look at this data and process the image!

astrophotography telescope

The William Optics RedCat 71 and ZWO ASI2400MC Pro. 

The EQ6-R Pro has proven itself to be reliable and work well in my cold Canadian winters, every time. In fact, the temperature dropped to -15 degrees Celsius throughout the night during this imaging session.

The telescope is a William Optics RedCat 71. This has become my go-to travel telescope, as it offers an excellent balance between focal length and portability. This telescope weighs about 7 lbs, making it a great option for those trying to travel light. 

The camera attached to the Cat 71 is a full-frame one-shot-color model, the ZWO ASI2400MC Pro. This allows me to pull in an impressive amount of sky in a single shot at the telescope’s native focal length of 350mm.

I was very excited to test this camera when it first arrived, as I view it as the dedicated astronomy camera equivalent to my Canon EOS Ra mirrorless camera. It offers a massive full-frame, back-illuminated color sensor with TEC (thermoelectric cooling).  

I have enjoyed using this camera on several projects over the past few months, including my best ever image of the Iris Nebula and the Pleiades. This 24-megapixel camera captures huge images with incredible detail when zooming in. 


I use the ZWO ASIAIR Plus to run my imaging session. This device allows me to wireless run the imaging session, controlling everything from autoguiding to setting the sequencing plan. 

The ASIAIR Plus replaces my laptop computer, which means I have less to pack on my astrophotography excursions. I control everything from my smartphone and have precise control over things like the focus and framing of my target.

I did not use a light-pollution filter to capture this scene, hoping that the Bortle 4 skies would be enough to bless me with clean sub-exposures in broad-spectrum light. I keep an empty Starizona filter drawer in front of the camera to achieve the recommended back-focus for my camera. 

location of my telescope

Setting up my telescope on the property at the Airbnb.

The cabin I stayed in was very cozy and warm. I was able to set up and run my telescope outside using a long extension cord (through a window) to power the mount. 

Because I used the ASIAIR wifi controller to run my imaging session, I could monitor the sequence and make adjustments to the camera from inside of the cabin.

My Camera/Telescope Tilt Issues

I think I’ve identified a tilt issue on this system. Tilt just means that the image sensor of my camera isn’t perfectly flush with the image plane of the scope.

A big sensor like the one on the ZWO ASI2400 is very demanding in this regard. When using this combo, I noticed that the stars on one side of the image always start to elongate.

At this point, I am unsure whether the tilt issue is due to the optics of the telescope, or the camera sensor itself. I believe it is the optics, as I did not notice this issue when attaching the ASI2400MC Pro to another telescope (SW Esprit 150).

tilt issues in astrophotography

A diagram of tilt issues in an astrophotography optical train. ZWO ASI Article.

Unfortunately, these rare clear nights don’t allow much room for tweaking and testing, so I’ll have to live with it for now and avoid placing my target in the ‘danger zone’ side of the image.

The viewers of my YouTube channel have offered some helpful suggestions to help me correct the issue. I know that some people swear by the CCD Inspector to fine-tune their optics, but I have not used the tool myself. 

For now, I will continue to work on finding a solution so I can fully utilize the entire field of my telescope with a full-frame camera attached. 

Related Article: The Best Astrophotography Telescope for a Beginner

Image Processing

To create the intermediate file for processing, I stacked 32 x 4-minute exposures (with 20 dark frames) in DeepSkyStacker. This produced a calibrated master file with just over 2 hours of total exposure time. 

The image below represents the ‘before’ image (stacked), with very few image processing techniques applied. As you can see, the image is much duller and less dynamic than the final image I produced.

This should give you a better idea of what to expect ‘out of the camera’, whether you are using a DSLR/Mirrorless, or a dedicated astronomy camera.

the before image

My “before” image of the Boogieman Nebula and M78.

At this stage, all that has been applied to the image is a quick stretch to the linear file and some background extraction. You may notice the blue light on the right-hand side of the frame, which is a stacking artifact of a bright flare emitted by the star, Alnitak.

The Boogieman Nebula and M78 cover a wide area of sky (3 degrees +), and unless you are using a wide-field optical instrument (350mm or wider), you likely won’t capture both objects in the same field of view. Even using the full-frame ASI2400MC Pro and 350mm RedCat 71, the objects were closer to the edges of the frame than I was comfortable with. 

sensor view

When planning your next deep-astrophotography project, make sure to check and see what your field-of-view will look like using your specific camera and telescope combination. For this process, I use the “sensor view” tool in Stellarium to see if my intended target is a good fit for my system. 

During the final stages of setting up my imaging session, I had to precisely rotate the camera to match the framing shown above. The bright star, Alnitak, made this process much easier. Bright stars in the field give you a near-real-time reference point to aid in the framing process. 

image processing guide

Related: My Astrophotography Image Processing Guide

One of the key aspects to processing the Boogieman Nebula was to carefully preserve the natural, diverse mix of colors in the area. Barnard’s Loop is vibrant red, while the LDN 1622 and the Messier 78 region include several blue and yellow stars.

Star reduction was critical to draw more attention to the nebulae structures, without going overboard and destroying the natural beauty of a filterless, broad-spectrum image. In the end, I would have preferred to have had double the amount of exposure time, but I think the dark skies helped me produce high-quality data in such a short period of time. 

My Final Image

I ended up with 32 x 4-minute sub-exposures on the Boogieman Nebula and M78 (2 Hours, 8 Minutes total exposure). My camera tilt issue meant that I needed to crop the image down from about 80% of the original frame.

I am thrilled to have finally photographed the Boogieman Nebula, especially during a cloudy winter like the one we’ve had this year. Click the image for a larger view:

Boogieman and M78

The Boogieman Nebula, Barnard’s Loop, and Messier 78 in Orion. 

Final Thoughts

As brief as the experience was, it felt so good to be under a sky full of stars again. I know my videos have been a little staggered lately, but it’s just because I need to feel the energy of this hobby firsthand to really get into it.

I don’t want to force the creative process, as much as it pains me to watch 2 weeks go by without posting a video. I want to share exciting moments and experiences that inspire you to get out and photograph the night sky yourself.

That’s what excites me, and hopefully, you appreciate them too.

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William Optics RedCat 51 Review

|Telescopes|35 Comments

William Optics is a company known for creating high-performance apochromatic refractors and constantly updating and refining their designs. The RedCat 51 Petzval APO is the latest creation from the company that can’t sit still, and it is bound to shake up the industry once more.

I am fortunate enough to have been granted early access to this exciting Petzval apochromat that debuts in early March 2019.

William Optics RedCat 51

What makes the William Optics Redcat 51 so special? The 4-element Petzval design, unique focal length, and helical focuser. The sleek red finish of the RedCat 51 signals its individuality and charm. It is unlike any other astrophotography telescope on the market and one that I have been waiting to get my hands on since reviewing the early concept designs last year.

While shooting the unboxing video for the RedCat, I came to the conclusion that this is hands down the most beautiful looking telescope I have ever seen in terms of style and design. This is a signature quality of the William Optics brand and they continue to push the envelope with new and dramatic concepts.

Update 2020

In early 2020, William Optics announced a “Nightcat” version of their popular imaging refractor exclusive to OPT. The RedCat 51 and SpaceCat have become difficult to find, so the NightCat version that debut’s in June might be a good option. 

It’s essentially the same telescope, but includes the new guide scope mounting hardware, a longer dovetail, and a slick new color scheme. If you are having trouble finding a RedCat in stock, you may also want to consider the Radian Raptor 61

The William Optics RedCat 51

The design goals for the RedCat included creating an affordable refractor that uses the highest quality glass and delivers a flat imaging field with unmatched color correction. In this post, I’ll break down the specifications of the RedCat and explain why I think this little quadruplet will be one of the most sought after products in 2019.

Have you ever seen a more dramatic video for an astronomy product in your life?

The RedCat bridges the gap between an astrophotography telescope and a telephoto lens.

prime lenses

The 250mm focal length and F/4.9 focal ratio mean that the RedCat can be enjoyed as much by wildlife photographers as it is by amateur astrophotographers. The helical focuser makes focusing fast-moving targets such as birds much easier than ever before.

For those of you that don’t know, I am also an avid bird photographer. Once I discovered the clarity and sharpness provided by an apochromatic refractor telescope, I began using my astrophotography telescopes for bird photography. These telescopes were too heavy to use handheld and were challenging to focus on moving subjects.

Roughly 8 years later, William Optics releases a high-end apochromatic refractor that targets the wildlife photography market. The RedCat encapsulates two of my greatest passions (astrophotography and bird photography) in a single product.

Andromeda Galaxy RedCat 51

The Andromeda Galaxy captured using the RedCat 51.

The RedCat 51 is small, beautifully designed, and versatile. The early astrophotography image examples shared by William Optics are breathtaking. Aside from looking good, and some promising looking results in terms of performance, the RedCat 51 has some handy features to improve the user experience.

Before I cover items such as the filter slot and modular mounting options, let’s dive into the core specifications of the RedCat 51.

RedCat 51 Specifications:

  • Optical Design: Petzval Apochromatic Refractor (4 elements in 3 groups)
  • Lens Type: Prime
  • Diameter: 51mm
  • Focal Length: 250mm
  • F-Ratio: F/4.9
  • Weight: 3.2 lbs
  • Focuser: Calibrated Helical
  • Mounting Style: Vixen/Arca-Swiss

RedCat 51 mounted to an iOptron SkyGuider Pro

The RedCat 51 mounted to an iOptron SkyGuider Pro.

Focal Length: 250mm

First off, the RedCat 51 has a focal length of 250mm. What does this mean for astrophotography? It means extremely wide-field deep sky images. If you consider a 480mm refractor to be a wide-field ‘scope, the RedCat is nearly twice as wide!

Massive deep sky objects such as the Carina Nebula will fit into the image frame in their entirety. Large nebulae that traditionally fill the frame in a typical wide-field setup are captured with plenty of surrounding space and additional star clusters and nebulae in the frame.

Until the RedCat came along, 250mm was a focal length reserved for those that employ a prime camera lens for astrophotography. Now amateur astrophotographers have the option of using a flat-field APO that easily mounts to their existing equatorial mount for deep sky imaging at this magnification range.

For wildlife photography, this focal length is also quite useful, especially when you consider the all-important f-ratio of this lens. 250mm is enough reach for many larger birds such as hawks and owls, but will require a steady hand and gimbal head for the best chance of a sharp shot. 

For nature and wildlife photography, the RedCat 51 has a minimum focus distance of 3.7 meters. This can be improved to under 3 meters with the use of the 2″ extension nose piece from the diagonal. By adding even more extension tubes, the RedCat can even be used for macro photography of small insects. 

William Optics RedCat 51 APO

The FPL-53 Objective lens of the RedCat 51 Petzval APO.

Focal Ratio: F/4.9

When it comes to photography (of filming) birds, it’s all about light. Fast shutter speeds are required to capture a bird in motion, and this demands a fast lens to adequately expose the shot. F/4.9 isn’t incredibly fast in the world of camera lenses, but when you consider that this is essentially a refractor telescope – it’s about as much light-gathering power as you’ll find on the market.

For comparison, the RedCat is almost a stop faster than the extremely popular Canon EF 400mm F/5.6L lens. William Optics has released some incredible wildlife footage shot using the RedCat, a testament to this quality. Low light situations such as a cloudy day, made wildlife photography tough with my old F/6 William Optics Z72. The speedy RedCat is a completely different animal.

51mm Lens Diameter

As the name eludes to, the RedCat has a 51mm objective lens. In the world of astrophotography telescopes, this is absolutely tiny! If you thought the adorable little Zenithstar 61 was cute, wait until you see the RedCat. But this kitten has claws (I couldn’t resist).

The 51mm objective lens on the RedCat is made from top quality FPL-53 and FPL-51 glass (synthetic fluorite) which creates a flat frame image from corner to corner, even when utilizing the entire image circle with a full-frame camera.

The small size of the RedCat means keeping the overall weight to a minimum, despite the extra glass. The RedCat 51 weighs only 3.2 pounds even through the design requires 4 elements in 3 groups. For owners looking for a high-end telescope to mount on the iOptron SkyGuider Pro, the RedCat is an ideal candidate.

Lens Structure: Petzval

A Petzval lens design involves a low-dispersion doublet in combination with two elements farther down the optical path to both speed up the f-ratio of the telescope, and flatten the image field. There is no need to use a field flattener with the RedCat, adding to its simplicity and practicality in the field.

Petzval Lens Design

The Petzval quadruplet lens design is well corrected and incredibly sharp. You can expect pinpoint stars to edges of your image. If you don’t believe me, have a look at this image of the Witch Head Nebula taken using the RedCat 51 by Mehmet Ergün.

These traits will surely make the RedCat a popular choice for high-resolution deep sky astrophotography imaging. Portability and design aside, the RedCat is an affordable option for those looking to own a top-of-the-line astrophotography telescope. A comparable refractor on a much larger scale is the Takahashi FSQ106.

RedCat 51 example images

Example images taken using the William Optics RedCat 51 on Flickr.

In mid-February 2019, Wei-Hao Wang shared an incredible image of the Running Chicken Nebula using the RedCat 51 with a modified Nikon D800 on Astrobin. The full-size image really showcases the color correction and flat-field qualities of the optics. 

I had a chance to test the RedCat 51 on the night of the full moon. This is not an ideal time to capture deep sky objects in broadband true color,  so I used an Optolong 7nm Ha filter inside of the RedCat. The image below was captured using a modified Canon EOS Rebel T3i (600D) through the RedCat 51 APO.

I stacked 33 sub-exposures of 4-minutes @ ISO 1600 each to create a total integrated exposure of 2 hours and 12 minutes. The 4-minute sub-exposures were accomplished thanks to the accurate tracking of the iOptron SkyGuider Pro. 

rosette nebula redcat 51

The Rosette Nebula in Ha – RedCat 51 + Canon DSLR

Helical Focuser

Yes, a helical focuser! This design aspect completely changes the user experience of the RedCat, whether you use it to photograph the night sky or a Black-crowned night heron. I have used a number of apochromatic refractors for daytime photography in the past, but none of them felt natural because of the rack and pinion focuser.

Aside from the impressive lens design, the helical focuser is the single biggest differentiating factor between the RedCat and a typical imaging APO. The focuser drawtube is calibrated and features printed mm spacing marks for precise adjustments. The black textured focuser ring is made out of soft rubber for a comfortable grip.

Adjusting focus during frantic wildlife photography moments is now much more fluid and responsive, while the precision and rigidity needed for deep sky astrophotography are retained. The focuser tension ring allows you to precisely control the level of friction desired, and also can also lock the tube in place when needed.

astrophotography examples

Some of the deep sky images I have captured using the William Optics RedCat 51 and a DSLR camera.

Field Rotator

The field rotator resembles the face of a luxury brand watch, which is exactly the inspiration William Optics used when designing the rotator markings on the RedCat. Every degree of the field rotator is marked to help aid in the process of creating a mosaic. There is a small white arrow on the M48 adapter to use as a reference point when setting your camera orientation.

This level of attention to detail is noteworthy, as this subtle feature indicates input from actual amateur astrophotographer needs.

You’ll find that many of the hidden “extras” on the RedCat 51 follow this mindset as well, including the small white Teflon rings inside of the mounting ring. This small, yet thoughtful detail allows the user to smoothly rotate your imaging train. 

M48 fied rotator

The field rotator includes markings for each degree of rotation.

M48 Thread

The M48 thread adapter allows you to fasten your DSLR or dedicated astronomy camera to the RedCat for astrophotography or daytime photography. The imaging circle completely covers a full-frame camera sensor for edge to edge illumination with a flat-field.

Speaking of covering your camera sensor, the M48 adapter includes an internal thread for 48mm (2-inch) threaded filters. This is a convenient location to place your favorite light pollution or narrowband astrophotography filter.

Owners of Canon, Nikon, Sony or Pentax cameras will be happy to know that their camera bodies are a perfect fit for the RedCat with the necessary t-mount and adapter hardware. The M48 end adapter must be removed to apply the matching red William Optics erecting diagonal.


Mounting Base and Lens Collar

The base of the RedCat 51 was specially designed to avoid adding extra weight to the telescope, yet provides a reliable platform for the demanding positions of astronomical imaging. The matching red low profile dovetail bar can be used with either a standard Vixen mount saddle or the photography-based Arca-Swiss style mounting bracket.

The dovetail plate includes standard ¼ inch threads and simply needs to be flipped over to accommodate your desired mounting configuration. Deciding on the configuration of this aspect of the telescope will depend on your primary use of the RedCat.

The optical tube itself can also rotate easily thanks to the lens collar and release knob. This is similar to the design you’ll find on high-end telephoto camera lenses, but with 2 extras. There are modular mounting options on the lens collar. Here, you can fasten accessories such as a shotgun microphone or red dot finder scope.

Integrated Bahtinov Focusing Mask

To top things off, William Optics has included their signature diffraction spikes Bahtinov mask in the lens cap. This feature is handy for DSLR astrophotography imaging sessions when you need to quickly and accurately confirm the focus of your target. You simply need to aim the telescope towards a bright star to create the diffraction spike pattern.

The elongated star patterns displayed when pointed at a bright star create an obvious and distinct guideline to reference when using adjusting the helical focuser. The clear acrylic design of these masks makes them much easier to use than the traditional opaque black Bahtinov masks. 

star spikes bahtinov mask

You may have also noticed the color-matched steel William Optics Vixen-style base attached to the iOptron SkyGuider Pro. This base mount also fits the Sky-Watcher Star Adventurer Pro and adds some serious stability to and improved aesthetics over the original base. The package also includes a 4.5″ red extension bar for the counterweight, that I regretfully forgot to install before filming the video.

Comparable Telescopes

You may be asking yourself if there are alternatives to the RedCat to consider, with a comparable optical design and size. Although the Vixen FL55 does not share a Petzval design, it is an ultra-wide field fluorite refactor with a 55mm lens diameter. The focal length of the Vixen FL55 is 239mm, with a focal ratio of F/4.3 (with the optional reducer used). The Vixen model does not include a carry case orBahtinov mask in the price, and requires an additional reducer for maximum usefulness.

The Takahashi FS-60 CB is also a direct competitor of the RedCat, although its design mirrors the WO Z61 more so than the RedCat 51. This is another compact fluorite refractor, and features a focal length of 335mm, at F/5.9.  The Takahashi name carries with it a  premium price. The optical performance of this 60mm refractor is indeed impressive, yet it does not have the unique features of design of the RedCat in a complete package.   

RedCat alternatives

RedCat 51 Alternatives, the Vixen FL55 and Takahashi FS-60CB.

The Radian Raptor 61 has comparable specs to the William Optics RedCat, at a 275mm focal length at F/4.5. The Raptor 61 uses a 10:1 rack and pinion focuser in place of a helical focuser and includes high-quality hex rings to mount the telescope. You can watch my video explaining my involvement with this project here: I Designed My Ultimate Telescope

Radian Raptor 61 Review

The Radian Raptor 61 with the optional electronic focuser.


When I mentioned that the RedCat 51 can be used as a  daytime wildlife photography lens, you may have wondered whether the RedCat will work with the autofocus function of your DSLR. I have some good news. Yes, the RedCat 51 can be used with autofocus!

But there is a catch (two actually). You will need to use the TechArt Pro adapter that includes a built in motor for manual lenses. This system only works with certain Sony DSLR cameras, which means for Canon or Nikon shooters, you’ll have to make due with manual focusing of the RedCat 51.

The system relies on the phase-detect autofocus system found on modern Sony cameras such as the Sony a6300, a6500, A7ii, and A7Rii.

autofocus with RedCat

The RedCat mounted to a Sony a7R and the TechArt Pro adapter.


The package William Optics sent to me included a number of extras, including the Canon EOS T-Mount adapter, and the dedicated erect image diagonal. The diagonal will hold a 1.25″ eyepiece for visual observing, or spotting scope purposes. The Canon EOS T-ring included with the RedCat is the most stylish looking camera adapter I have experienced to date.

The diagonal is of little importance to those that will use the RedCat 51 exclusively for deep sky astrophotography, but it is a nice option for those that like the choice of using this telescope for visual use. This is of particular interest to anyone who purchases the RedCat with plans on using the telescope as a spotting scope for wildlife photography.

The RedCat can be mounted to a traditional photography tripod for crisp views at 250mm. 

Erect image diagonal

The dedicated RedCat erect image diagonal fastened to the telescope.

Removing the M48 Adapter

To install the dedicated erect image diagonal on the RedCat 51, you need to remove the 48mm adapter. Use a small Allan key (0.7mm) to unscrew the three grub screws just enough so that you can turn the M48 adapter counter-clockwise with the field rotator locked. You should eventually feel the thread release so you can unscrew the adapter.

48mm filter for RedCat

Remove the M48 Adapter on the RedCat to fasten the diagonal or install a 2-inch filter.

The diagonal can then be threaded directly to the base of the field rotator for visual observing or spotting scope purposes.

The 48mm filter threads are also located between the M48 adapter and the field rotator. This is a discreet location in the imaging train to thread a light pollution filter inside of the RedCat 51.

The Bottom Line

The price tag of the William Optics RedCat 51 may seem a bit steep at first, but considering the pedigree of this refractor, it’s right on the mark. Creating an affordable option for those looking for a premium imaging APO in a small package was the overall goal of the RedCat design. I believe the RedCat is poised to have a big year, and look forward to the official unveiling at NEAF. 

If you have interests in both wildlife photography and deep-sky astrophotography as I do, you might feel like the RedCat was designed specifically for you. William Optics is a brand that continues to innovate and create original products. In a world full of copycats, this little APO stands in a category of its own. 

The RedCat 51 can be very difficult to find. In 2020, William Optics introduced the “Nightcat”, a special edition version of the telescope that is the successor to the newer “Spacecat” version (see below). 

nightcat 51

See the RedCat 51 in action on YouTube: Deep Sky Astrophotography with the RedCat 51


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