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Refractor

Why You Should Start with a Refractor Telescope

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If you’re getting started in deep-sky astrophotography, I believe that a compact apochromatic (APO) refractor telescope is the best possible choice.

A compact APO refractor is portable and lightweight, making it a smoother transition from the camera lenses you may be used to. In fact, in many ways, a high-quality apochromat is very much like a telephoto lens. 

If you’re interested in photographing nebulae and large galaxies in the night sky through a telescope, this article should shed some light on the decision-making process ahead of you. 

astrophotography with a refractor telescope

My first refractor telescope was an 80mm Explore Scientific apochromatic triplet. 

Introduction

Throughout the past 8 years of deep-sky astrophotography, I’ve made lots of mistakes. In the beginning stages, I made critical errors in selecting and setting up equipment. 

From the beginning, my goal was to capture deep-sky images of nebulae and galaxies. This type of astrophotography requires the most advanced equipment and demands a careful setup routine. 

The type of telescope you choose early on can have a dramatic impact on the complexity of your deep-sky astrophotography setup. In my experience, a compact, wide-field refractor offers an improved user experience over the other telescope types during the acquisition stages of astrophotography.

For example, I began taking my first deep-space images with a reflector telescope. If I could go back and I do it all over again, I would have chosen a compact, wide-field refractor to start astrophotography with. 

setting up telescope

These days, I use a refractor telescope for 90% of my astrophotography. 

I am not saying that there is anything wrong with starting your astrophotography journey with a Schmidt-Cassegrain Telescope (SCT) or Newtonian Reflector, but I believe you will have some additional challenges to overcome early on. 

No matter what type of photography experience you have going in, deep-sky astrophotography through a telescope will have a number of challenges to overcome early on.

This includes understanding how to polar align an equatorial mount, how to focus your camera on a faint deep-sky object, and how to attach your camera to the telescope. two out of the three challenges become more difficult if you’re not using a wide-field refractor to start.

The statement above is not theoretical, I personally experienced these frustrating moments in my backyard years ago. I should have started with a compact refractor telescope. 

deep-sky astrophotography

A recent photo of NGC 7822 captured using a color camera and a 100mm refractor.

I Should Have Started with a Refractor

I often see newcomers to deep-sky astrophotography starting with a telescope that will make an already-challenging hobby even more difficult. I went through this experience personally, and this is what happened. 

My first astrophotography telescope was a Meade LXD55 6″ Schmidt-Newtonian. I purchased this reflector telescope from a local camera store second-hand, for a great price. 

At the time, I had very little knowledge of telescope-types, optical designs, or astronomy in general. I took the advice of the salesman at the store, and he assured me that “this telescope can be used for astrophotography”.

comparing a reflector to a refractor

The telescope I started taking pictures of space with.

First off, he was right. It could certainly be used for astrophotography, and I even found astrophotography images online taken by others using this particular model.

The problem was, this type of telescope presented some pretty daunting challenges to overcome. My long term love for astrophotography was at stake, as a poor experience could potentially sour me on this new adventure. 

Thankfully, I kept a positive mindset throughout the process despite having limited knowledge (and limited funds). 

This was my First Astrophotography Telescope

astrophotography telescope setup

My first telescope for Astrophotography was NOT a refractor, and it presented some challenges.

I mounted the Meade LXD55 SN6 to a Celestron CG-5 (Advanced Series GT) computerized telescope mount. The GoTo tracking mount was my biggest investment in the hobby early on, and looking back the mount was performed surprisingly well. 

A Schmidt-Newtonian is a promising instrument for astro-imagers. The corrector plate helps you collect images with less coma than a traditional reflector design.

Essentially it’s a catadioptric telescope that combines elements from both the Schmidt camera and the Newtonian reflector. A spherical primary mirror is combined with a Schmidt corrector plate to correct the image. 

It looks capable enough in the picture, so what’s wrong with starting your astrophotography adventure with a Newtonian Reflector, Schmidt-Cassegrain, or a Ritchey–Chrétien? 

Some would argue that there is nothing wrong with any of these choices, but here’s why it wasn’t a good fit for me:

It was Heavy and Difficult to Balance

It wasn’t a bad telescope, and I even managed to collect my first-ever deep-sky image with it. I really had no idea what I was doing at this point, and was absolutely thrilled to finally captured a tracked deep-sky object in the night sky. 

The problem with this old Meade telescope was that it was not a great type of telescope to start with. Looking back, a compact refractor telescope would have made my life a lot easier at the time. 

For starters, it was rather heavy and difficult to balance. It was at the maximum payload capacity of my equatorial mount (Celestron CG-5), and I even had to use some “custom” counterweights to achieve balance.

In the astrophotography world, you never want to have your telescope rig reach the weight limits of your telescope mount. This puts extra stress on the equatorial drive system and often results in poor tracking. 

first picture of Andromeda

My first picture of M31 (Andromeda) using the Meade reflector telescope (July 2011).

It Had Too Much Magnification

In my opinion, the telescope had a little too much focal-length as well. Extra magnification can be great for pulling in small targets, but it’s also more demanding on aspects such as pointing accuracy, tracking, and focus. 

Prime-focus astrophotography involves attaching your camera directly to the focuser of the telescope, with no additional eyepieces or lenses between them. That means that the native focal length of the telescope decides the field-of-view (FOV) and scale of the objects you shoot. 

The SC6 had a focal length of approximately 762mm, which could be considered to be a “mid-range” focal length. For comparison, my William Optics Zenithstar 73 refractor has a focal length of 430mm. 

I really shouldn’t complain about the 762mm focal length (FL) of the 6″ Meade, some amateur astrophotographers start out with an 8″ SCT with a demanding 2000mm+ FL. (I think I would have given up!)

The Focuser was Loose and Difficult to Secure

As newcomers will tell you, achieving a tight focus on your deep-sky subject can be challenging early on (Here are some tips).  It’s hard enough to find the optimal focus distance without worrying about the focuser “slipping” out of position on its own. 

Like a traditional Newtonian telescope, the focuser is placed near the front of the optical tube to collect light from the secondary mirror. This creates a challenging situation in terms of balance, especially when using a heavy, full-frame DSLR camera. 

The weight of my camera would put stress on the objective end of the optical tube. Despite using the locking screw, the DSLR would eventually fall downwards into the focuser as the night progressed. I constantly had to re-adjust focus after 4-5 images.

In general, I find reflector telescopes to be more challenging to focus than a refractor, and that was certainly the case with this F/5 Schmidt-Newt.

Start with a Compact, Wide-field Refractor

I’m not saying that a refractor telescope is the only way to go, but I think you’ll find that the astrophotography community generally agrees with me on this one. To be more specific, an apochromatic refractor is best. 

Refracting telescopes use lenses, not a mirror, to deliver crisp views through the eyepiece, and high contrast, well-corrected color images with your camera. 

In late 2011, early 2012, I invested in an Explore Scientific ED80 Triplet APO refractor. The reason I call this an “investment” is that not only did this telescope reward with me with my best images to date, but quality glass hold their value quite well.

ED80

Below, is an old photo of my 80mm refractor telescope on a Celestron CG-5 equatorial telescope mount. The difference between the images I was collecting with the Schmidt-Newt and the APO refractor was night and day. 

The stars were small and well-corrected (all of the colors came to a focus at once), and I no longer dealt with coma, reflections, and dramatic vignetting. 

Explore Scientific ED80

My first refractor telescope was an Explore Scientific ED80. 

Another advantage this telescope had was the field of view. Being a beginner, I had my heart set on capturing some of the most iconic deep-sky objects like the Orion Nebula, Andromeda Galaxy, and the Pleiades star cluster. 

The focal length of this telescope (480mm) was a perfect fit for all of these targets. I didn’t need to worry about creating a mosaic to fit the entire object in the frame. Images like this were the reason I got into astrophotography in the first place.

Finding targets in the night sky became a lot easier thanks to the forgivingly wide field of view. Even if the pointing accuracy of my computerized equatorial telescope mount was off, I could usually find my intended deep-sky target within the field-of-view of my first slew.

best telescopes for astrophotography

See my list of recommended refractors for astrophotography.

The first summer (2012) with my Explore Scientific 80mm refractor telescope was an exciting one. I captured several amazing photos of deep-sky objects with my Canon EOS Rebel Xsi DSLR. 

The most exhilarating photo came in July of 2012 when I attempted to photograph the Andromeda Galaxy with my 80mm refractor and stock Canon DSLR. The image was a monumental improvement over my attempt the previous summer. I was especially thrilled at the clarity of the image and natural star colors recorded. 

astrobackyard first andromeda

My first successful image of the Andromeda Galaxy (July, 2012). 

The Perfect Astrophotography Telescope

A high-quality doublet or triplet apochromatic refractor is capable of producing sharp, flat, well-corrected images. Almost all types of telescopes are capable of impressive astrophotography images, but some make you work a lot harder for it. 

For example, a Newtonian Reflector presents an advantageous light-gathering ability and an affordable price-per-aperture. However, Newtonians require regular collimation and adjustments to avoid coma and perform at their best.

An apochromatic refractor will perform much better in terms of photography than its less expensive achromat counterpart. 

The objective lens (consisting of 2 or more pieces of glass) of an apochromatic refractor is designed to focus light to the same point, and correct chromatic aberration. As you can see in the diagram below, an apochromatic objective focuses different wavelengths of light closer to the same point than an achromat does.

apochromatic vs achromatic

“The strict definition of apochromatism is having three wavelengths of light focusing to the same point.  This normally requires a third lens element in the objective.  The normal configuration is a positive, low-dispersion crown, combined with two high-dispersion flints, one negative and one positive.  The lenses can be cemented, air-spaced, or a combination thereof.” Starizona.

For a technical description of how a refractor telescope works, and the refractive index of certain mediums, check out this informative article

Pros and Cons of a Compact APO Refractor Telescope

There are some pros and cons to using a compact refractor telescope for astrophotography, and here they are:

Pros:

  • You can mount them to modest, entry-level equatorial mounts
  • Refractors are compact and lightweight compared to other telescope designs
  • The focusers are solid and easy to focus
  • They offer a similar experience to a high-end telephoto camera lens
  • The image quality potential for astrophotography is exceptional
  • Refractors do not require regular collimation or optical adjustments
  • They offer a forgiving, wide field-of-view

Sky-Watcher Star Adventurer Pro Review

You can mount a small refractor on a portable tracking mount like the Sky-Watcher Star Adventurer.

Minus:

  • They are the most expensive telescope type (price per aperture)
  • They are not well-suited for high-magnification planetary imaging
  • The apertures are often too small to observe faint deep sky objects
  • Galaxies and smaller DSO’s need 1000mm+ for an up-close view

My favorite astrophotos of all time were all taken using a refractor telescope. From my first experiences with the Explore Scientific ED80 to the massive Sky-Watcher Esprit 150 Super APO, refractors are my number one choice for astrophotography. 

The image below shows a William Optics Zenithstar 73 refractor mounted to a modest Sky-Watcher HEQ5 GoTo telescope mount. My DSLR camera is attached to the focuser of the telescope for deep-sky imaging at 430mm.

This entire ensemble can be lifted up and moved around the yard on a moment’s notice, so I usually keep the entire imaging system ready to go in the garage.

A setup like this is also refreshingly easy to travel with. It does not take up very much space in my vehicle and can be re-assembled quickly. 

telescope equipment

A portable deep-sky imaging setup with a 73mm refractor telescope. 

This versatile and reliable rig does not come at the expense of performance either. A small setup like this is capable of producing incredible astrophotography images using a DSLR/Mirrorless camera or a dedicated astronomy camera.

The photo below shows the image captured using the telescope setup pictured above in my video titled “Taking a Picture of the Andromeda Galaxy“.

This image includes 67 x 120-second exposures using a Canon EOS 60Da. 

Andromeda Galaxy

My latest version of the Andromeda Galaxy using a DSLR and a small refractor telescope. 

My Newtonian Reflector Collects Dust

In 2014, I decided to purchase an 8″ Newtonian Reflection, the Orion 8″ F/3.9 Astrograph Reflector. The idea was to add some light gathering power and a little more focal length at an affordable price. 

However, I had become used to the quick and setup time of my 80mm refractor, and balancing the big optical tube on my Sky-Watcher HEQ5 mount was time-consuming.

Also, I had to regularly collimate the tube before each and every imaging session. Perhaps the telescope was perfectly collimated before I attached my camera, but I always had to make sure before spending a night collecting images. 

I did manage to capture some impressive images with this setup, but surprisingly, the added aperture did not add the extra “punch” to my images I was looking for. In the end, this telescope was a lot more effort, for very little (if any) benefit to my astrophotography.

reflector vs. refractor for astrophotography

I do not use my 8″ Newtonian Reflector very much these days.

What Size and Brand Should You Buy?

I’ve used refractor telescopes with an aperture of 51mm, all the way up to 150mm. Smaller, compact APO’s are much more practical and affordable, yet do not sacrifice as much performance as you may think.

For example, the image of the Lagoon Nebula and Trifid Nebula region of Sagittarius was captured with a miniature (51mm aperture) William Optics RedCat APO and a DSLR camera. This quadruplet refractor weighs just 3.2 pounds and can fit in your carry-on bag

wide field deep sky astrophotography

Nebulae in Sagittarius using a William Optics RedCat 51 APO. 

Nearly every telescope manufacturer builds refractor telescopes, and I’ve had the opportunity to try many of them. I’ve had wonderful experiences using apochromatic refractors from Explore Scientific, William Optics, Meade, and Sky-Watcher.

William Optics compact doublets are very popular and rather affordable considering the optics used in their designs. The Zenithstar 73 APO is one such example, and a telescope I have personally taken a lot of beautiful images with.

The Sky-Watcher Esprit line of refractors is a step up, with the Esprit 100 Super APO (Triplet) being my most used refractor of all time. These telescopes are expensive and quickly grow in price as aperture is added. 

sky-watcher telescope

Setting up the Sky-Watcher Esprit 100 refractor telescope in the backyard. 

When choosing a refractor telescope for astrophotography, ensure that it is an apochromatic optical design, not an achromat. Also, ensure that the optical tube includes a robust, 10-1 speed focuser that can lock into position when needed. 

You’ll also need to confirm that the mounting hardware will allow you to mount the telescope to your equatorial mount, and add additional accessories such as a guide scope and camera for autoguiding. 

Make sure you invest in the appropriate field flattener for your refractor, as this extra glass lens will help flatten the field of view to the very edges of your picture.

Final Thoughts

If your astrophotography interests lie in taking images of nebulae and large galaxies, an apochromatic refractor should be your number one choice of telescope.

This category of deep-sky objects includes some of the most iconic wonders in space, and you could spend a lifetime capturing them.

Not only is an APO refractor a perfect fit in terms of focal length (native magnification), but the images with your DSLR/Mirrorless or dedicated astronomy camera will be extremely sharp and well-corrected.

If your looking to photograph the planets, a compact refractor is not for you. Smaller targets such as planets and many galaxies are not a good fit for a wide-field refractor.

But if you’re a fan of quick set up time, consistent results, and wide-field nebulae like the ones below, you simply cannot beat an APO refractor.

soul nebula

The Soul Nebula in Cassiopeia using a William Optics Zenithstar 73 APO. 

Pleiades

The Soul Nebula in Cassiopeia using a William Optics RedCat 51 APO. 

Recommended Refractors for Astrophotography

The following list of apochromatic refractor telescopes have all produced exceptional results for me personally, so I feel comfortable recommending them. They are all compact, wide-field instruments capable of producing images like the ones shared in this post. 

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William Optics RedCat 51 Review

|Telescopes|24 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.

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.

telescope

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, Bahtinov 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. This 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.

Autofocus

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.

Accessories

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. 

This telescope will be available in early March 2019. You can order the William Optics RedCat 51 at High Point Scientific

High Point Scientific

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

 

Related Posts:

William Optics RedCat 51 Official Product Page

William Optics Zenithstar 73 APO Review

Astrophotography in Costa Rica (Carina Nebula)

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The Explore Scientific ED140 Apo Refractor

|Telescopes|6 Comments

I am thrilled to tell you that I recently got my hands on a brand new Explore Scientific ED140 CF APO Triplet Refractor. If you’ve been following AstroBackyard for some time now, you’ll know how I feel about APO refractors in terms of astrophotography performance.

The refractor telescope design has many unique advantages when it comes to deep sky astrophotography. Specifically, an air-spaced triplet apochromatic optical design will share many of the same characteristics you’ll find on a high-end telephoto camera lens. The biggest difference is – they usually reach much further. (The ED140 has a focal length of 910mm)

The Explore Scientific ED140 CF

I won’t tell you that you need a 140mm refractor to enjoy deep sky imaging, because that’s simply not true. Instead, look at my experiences with this telescope as a window into the possibilities that await you in the future. By the time you have outgrown your little astrophotography telescope, maybe you’ll consider stepping up to the stunning Explore Scientific ED140 triplet apochromatic refractor.

I met up with the team at Explore Scientific last month at NEAF – and they asked if would try out their new ED140. Would you turn an opportunity like that down?

I didn’t.

In the video above, you’ll see me use the ED140 to capture a deep sky astrophotography image from my backyard. I decided to choose a target that could be completed in one night, using a one-shot-color camera. The great globular cluster in Hercules (M13) is a fitting choice for an incredible telescope like this, and the first globular cluster I’ve ever shot on my YouTube channel.

The Apochromatic Refractor Advantage

Before I get into the details of this giant APO, I’ll provide a little bit of backstory.

Back in 2011, I started using an Explore Scientific ED80 F/6 refractor.  For many years, I was thrilled with the images I was taking using the ED80 and a DSLR camera. If you like shooting wide-field targets such as the North America Nebula, the Andromeda Galaxy or the Pleiades, a small apochromatic refractor telescope like this is a superb choice.

using a refractor telescope for astrophotography

My early deep sky images using an Explore Scientific ED80 Triplet APO.

The only thing you’ll be missing out on with a small telescope of this size is the visual observing power and increased magnification that comes with an instrument with a larger aperture. A refractor in the 60-100mm range generally offers an extremely wide field of view, which is great most of the time.

If your primary interests lie in objects that require high magnification and light-gathering ability such as planets, you may want to think about a larger telescope. Photographing small galaxies, globular star clusters and solar system targets are not a small APO’s strong points.

The lack of chromatic aberration, coma or need for constant collimation make the refractor design my absolute favorite type of telescope design when it comes to deep sky astrophotography. However, to get the extra light gathering power found in larger telescopes, expect to pay a lot more per inch of aperture.

An F/6.5 Carbon Fiber Monster

A large refractor like the Explore Scientific ED140 not only offers the image quality and performance APO owners expect but also the reach and resolving power needed to capture planets and smaller deep sky objects. 5.5″ inches of aperture gives you the light-gathering power needed to soak in the delicate fine details of objects in space.

carbon fiber telescope

The carbon fiber tube of the ED140 is lightweight and strong

In my opinion, you can’t fully appreciate the additional aperture from a telescope like this without gradually working your way up in size. As I mentioned, I’ve had the pleasure of taking astrophotography images with many sizes of refractor telescopes – everything from a 61mm telescope to a 132mm. This has given me with some practical perspective about the difference extra aperture makes when it comes to astrophotography.

The Explore Scientific ED140 CF Triplet APO now holds the title of the absolute biggest refractor telescope I have ever used for astrophotography.

Core Specs:

  • Focal Length: 910mm
  • Focal Ratio: f/6.5
  • Tube Length w/ Dew Shield: 991mm
  • Diameter: 140mm
  • Weight: 21 lbs
  • Dovetail: Vixen

Explore Scientific ED140 CF Triplet APO refractor telescope

First Impressions

The first thing I noticed when I picked up the box, was how light it was. The Explore Scientific ED140 is noticeably light for its size, no doubt due to its carbon fiber construction. Despite being 8mm wider in aperture, this telescope is roughly the same weight as the William Optics FLT 132. The Carbon fiber tube doesn’t sacrifice strength for a lighter payload either. This versatile material is extremely strong and is also said to compensate for temperature fluctuations better than a steel tube.

Explore Scientific logo

With my gear staying outside in a non-insulated garage – I’ve never really had any issues waiting for my telescopes to cool down/warm up. However, I understand that this is something to consider for many amateur astrophotographers. I’m a big fan of the way this telescope looks, and not just because it matches my ED102. For those that appreciate aesthetics, the finish on this instrument is a real head-turner at star parties.

What’s Included?

As I have mentioned in the past, the accessories included with astrophotography telescope packages vary widely. Some will include everything from a dedicated field flattener to the guide scope, while others may not even include the mounting hardware and sell the optical tube on its own.

The Explore Scientific ED140 F/6.5 APO Triplet includes some impressive extras in their standard package.

Heavy Duty Carry Case

The first thing you’ll notice when you take this giant telescope out of the box is that it comes with a heavy-duty hard carry case. This looks identical to the case that came with my Explore Scientific ED102 CF – which has come in very handy when traveling with the scope. This case was rugged enough to get packed into my trunk with lots of heavy camping gear on top.

The carry case comes with a thick padded-foam insert that holds the ED140 securely. For those planning on traveling with the ED140 – this case is TSA approved.

hard carry case

The hard carry case is heavy duty and TSA approved

2″ Diagonal for your eyepieces

The ED140 telescope includes an Explore Scientific branded 2″ diagonal in the hard carry case. A diagonal reflects the image through the telescope on a 90-degree angle to provide a more comfortable experience using an eyepiece. This is an essential accessory for anyone who plans on using this telescope for visual use.

I have only ever used one diagonal before this one, and it was also an Explore Scientific “99% reflective” model. I must admit, I have not taken the diagonal out of the case yet, nor have I used the Ed140 for any visual observations yet.

In terms of visual performance, the large aperture and fast focal ratio (F/6.5) of this telescope mean that impressive views of both deep-sky objects and solar system objects are possible under the right sky conditions.

It’s not clear how long I’ll have this telescope for, but I’d love to test it out under the dark skies of Cherry Springs State Park next month.

Heavy-duty 3″ Hexagonal focuser

The 3″ hexagonal focuser is big and rigid, which is what you’d expect on a telescope of this size and price point. No doubt, most will use the ED140 will primarily be used for astrophotography, so it’s reassuring to know that Explore Scientific rates this focuser at a 10-lb payload. My camera gear is nowhere near that weight, but owners of large CCD cameras and filter wheels will appreciate this payload rating.

With the ZWO ASI294MC-Pro camera attached, I was easily able to find focus using this ultra smooth 10:1 dual speed focuser. Once locked, there is no “play” in this focuser. Meaning, no surprises while imaging due to the focuser shifting or jarring the camera.

3 inch hexagonal focuser

The 3-inch dual-speed hexagonal focuser on the ED140 is solid

Cradle Ring with Handle and Dovetail

Mounting the ED140 is easy due to the included cradle rings and Vixen-style dovetail plate. I really like this design, and it’s the same mounting style used on the 102mm version. Aside from making the telescope easier to manage, the handle portion is a great spot to mount an additional finder scope, center the guide scope, or attach a ball head and camera lens.

In the past, I’ve mounted a DSLR camera and heavy 300mm F/4L lens to the handle of the cradle rings. The 1/4″ channel running through the middle makes it easy to fasten additional gear to it.

cradle rings

The included cradle rings for the Explore Scientific ED140

Integrated Dew Shield

The integrated dew shield is large and stays secure. It’s quite stiff and tight, which I like. I can be confident that the dew shield will not slowly slip down the tube when the telescope is pointed upward.

Essential Astrophotography Accessories

Recommended Field Flatenner/Reducer

Currently, there is no dedicated field flattener for the ED140 APO. The team at Explore Scientific has assured me that a dedicated flattener/reducer will be available for this telescope soon. I plan to try out my 2″ StarField 0.8X flattener/reducer on this telescope to see if it’s a good fit.

Adding a Guide Scope

Upon opening the locking case, you may notice a lack of finder/guide scope with this package. I feel that most folks looking to upgrade to the ED140 CF will already have an existing guide scope, so it wouldn’t make sense to pay for another one as a part of this package.

Thankfully for me, the ED140 came with a pre-installed base (saddle) for a finder/guide scope. This means I don’t have to look for any additional mounting rings or add any extra hardware to the scope.

I’ve been able to use the Explore Scientific finder scope mount from my ED102 on this telescope. If you don’t already own this specific style of mount, you’ll need to order one. It’s a bit different than a traditional Synta-style saddle that you’ll find on the Orion branded products.

50mm Starfield Guidescope

The 50mm Starfield Guidescope is a great match with the ED140

Inside this mount, I’ve installed a 50mm Starfield guide scope. This is a compact, lightweight and wide field guide scope that pulls in numerous guide stars for autoguiding purposes. Ontario Telescope sells this guide scope as a package with the Altair GPCAM2 camera, making for a very convenient and complete autoguiding combo.

50mm Starfield Guidescope Complete Autoguiding Package

I haven’t talked about the StarField guide scope I’ve been using a lot lately, but I will in the near future. I will say that I’ve got 50 and 60mm versions that both do an excellent job of autoguiding when used with the Altair GPCAM2 mono guide camera.

 About the Ohara FPL-53 Glass

The most impressive feature of this refractor has to be the Ohara FPL-53 extra-low dispersion ED glass used in its triplet optical design. This is a top of line material and considered the best glass ever produced by Ohara.

FPL-53 Glass

The company mentions that the FPL-53 glass used in the Explore Scientific ED140 is very similar in characteristics as Hoya FCD-100. I’ve received numerous questions about the differences between the FCD-100 versions of the Explore Scientific telescopes and the original Hoya extra-low dispersion glass versions.

My ED80 and ED102 both used the original Hoya glass, and making a defined difference in image quality between these telescopes and FPL-53 is difficult. A refractive index comparison is needed to tell the subtle differences in these materials.

The bottom line is, the glass used in the Explore Scientific Triplet series APO’s have always produced incredible astrophotography images, and now they’re better than ever. FPL-53 is perhaps the finest glass you’ll find in a refractor telescope with characteristics closely related to pure fluorite.

The Meade 70mm Quadruplet APO and the William Optics Z61, Z73 and FLT 132 all use FPL-53 as well. This is a true diffraction-limited optical design that virtually eliminates chromatic aberrations and produces high-contrast images. This Explore Scientific telescope also utilizes proprietary EMD enhanced multi-layer coatings on all optical surfaces.

A versatile astrophotography workhorse

The focal length of the ED140 is 910mm. So, a great mid-range magnification at prime focus, perfect for most nebulae and the larger galaxies. My favorite emission nebula targets such as the Omega Nebula and Lagoon Nebula are the perfect size for this focal length.

The lack of a dedicated field flattener/reducer at this time means that I am forced to find a workaround if I want sharp stars to the edge of the field. My crop-sensor (APS-C) sized DSLR and astronomy cameras (ZWO ASI294MC-Pro, Altair Hypercam 183M) have relatively small sensors, so this is less of an issue. Full-frame camera owners looking to utilize the full imaging sensor size will definitely need a solution from Explore Scientific to fully enjoy this telescope.

backyard telescope

Mounting and Autoguiding

The ED140 is about 20 lbs, so a robust equatorial mount such as the iOptron CEM60 is needed to use a refractor of this size for deep sky astrophotography. During my first imaging run, I had tremendous success using the Starfield 50mm guide scope package for autoguiding.

Those looking for a plug-and-play autoguiding solution should certainly give the Starfield / GPCAM2 combo a look. Just remember that you’ll need an Explore Scientific style finder mount to attach it to the base.Deep sky astrophotography telescope

Final Thoughts

My “first light” with the Explore Scientific ED140 was a huge success, and that’s not always the case with a brand new telescope. This speaks to the reliable and painless experience a refractor telescope like this provides to amateur astrophotographers.  The ZWO ASI294MC-Pro turned out to be a great fit with the ED140 – with only the very edges of my image frame showing elongated stars (even without the use of a field flattener).

The broadband RGB image of M13 I captured was a pleasure to process, and clearly showed the difference the added aperture makes when it comes to astrophotography. The combination of longer focal length and extra light-gathering power resulted in my best version of the Hercules globular cluster to date.

Great Globular Cluster in Hercules

The Great Hercules Globular Cluster (M13) using the Explore Scientific ED140 CF 

This image uses 2 Hours and 9 minutes (129 frames) worth of total integrated exposure time using a ZWO ASI294MC-Pro Camera.

On June 15th, I captured the following image of the Trifid Nebula using the 140 under dark skies. For a behind-the-scenes look at the complete setup used for this photo, watch my video from the 2018 Cherry Springs Star Party

The Trifid Nebula

The Trifid Nebula using the Explore Scientific ED140 CF 

This image uses 3 Hours and 3 minutes (61 frames) worth of total integrated exposure time using a ZWO ASI294MC-Pro Camera.

 

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Cocoon Nebula with an 80mm Telescope

|Nebulae|0 Comments

IC 5164 – The Cocoon Nebula

Imaged with an 80mm Refractor

We have had a stretch of clear nights this summer, and I have been taking full advantage! This year I decided to spend some time in the sweet spot of the sky, Cygnus the Swan. This area of the night sky rises high overhead throughout the night, free from the Earths atmosphere.

My first target was IC 5164, The Cocoon Nebula. I have never attempted this object before because I heard it was quite difficult to image, and to be honest, I just didn’t like the look of it!

Cocoon Nebula 80mm

The Cocoon Nebula – Imaged with an 80mm Refractor Telescope

That all changed once I stacked my first night’s worth of images into DeepSkyStacker and saw the beautiful pink nebulosity and dust lanes start to appear. I became obsessed with adding as much time to this deep sky object as possible. I imaged the Cocoon Nebula for 3 consecutive nights, June 30, July 1 and July 2.

Photography Details

Total Exposure Time: 5 Hours (60 x 5 Minute Subs)

Telescope Mount: Skywatcher HEQ-5 Pro Synscan
Camera and Telescope: Canon Xsi (stock) Explore Scientific ED80 Triplet Apo
Guided with PHD Guiding
Stacked in Deep Sky Stacker
Processed in Adobe Photoshop CC

NGC 6960 – The Western Veil Nebula

Western Veil Nebula

NGC 6960 – Western Veil Nebula

Next up is the gorgeous “Witch’s Broom” Nebula, or more specifically, NGC 6960 – The Western Veil Nebula in the constellation Cynus.  I haven’t shot this object since 2012, with lackluster results back then.  This time however,  I photographed it under darker skies, with better guiding and focus.

Photography Details:

Total Exposure Time: 4 Hours, 41 Minutes (61 Frames)
Camera and Telescope: Canon Xsi (stock) – Explore Scientific ED80 Triplet Apo
Telescope Mount: Skywatcher HEQ-5 Pro Synscan
Guided with PHD Guiding
Stacked in Deep Sky Stacker
Processed in Adobe Photoshop CC

Canon Rebel Xsi: Now Modified

Now with a “Naked-Sensor” for better Astrophotography

I have some exciting news about the advancements in my astrophotography!  My next post will talk about my recent modification to my Canon Xsi to remove the IR Cut Filter. Stay tuned for a full post and description of this process!  I’ll give you a hint, I used the How to modify your Canon DSLR for Astrophotography tutorial video.

80mm Refractor Telescope

My astrophotography rig at dawn

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Rosette Nebula – Stock Canon DSLR

|Nebulae|4 Comments

How the Rosette Nebula looks with a Stock DSLR

Will an unmodified Canon DSLR pick up the red nebulosity?

Happy New Year! I was finally graced with some clear skies that showcased the beautiful winter milky way on Monday. The moon was about 19% lit, and didn’t set until about 10:30pm, so about half of data in the photo above was captured with the moon still out. The sky conditions were so fantastic on Monday, it was a shame I had to leave early to get a good night’s sleep for work the next morning.

The Rosette Nebula (Caldwell 49) is a large circular HII region. The open cluster NGC 2244 (Caldwell 50) is closely associated with the nebulosity, the stars of the cluster having been formed from the nebula’s matter.

Rosette Nebula Stock

 

Caldwell 49 – The Rosette Nebula
Imaged Monday, February 3, 2014

38 subs, 3.5 Minutes Each totaling 2 Hours 13 Minutes

I used the Explore Scientific 80ED telescope for this photo because the size of this object is quite large. I am quite happy with my end result, although I plan on processing the photo several more times to try and pull out as much detail as possible.

I highly recommend Noel Caboni’s “Astronomy Tools” action set for Photoshop. I found it very helpful when processing this image, and every other image I have taken. For the price of a cheap filter, you can drastically improve your astrophotos. Well worth it!

Complete Astrophoto Details

Telescope: Explore Scientific ED80 with WO Flat III 0.8x FR/FF
Tracking Mount: Skywatcher HEQ5 Pro Synscan
Guiding: Meade DSI Pro II and PHD Guiding
Guide Scope: Orion Mini 50mm
Camera: Canon EOS 450D (Stock)
ISO: 1600
Exposure: 2 hours 13 Minutes (38 x 210s)
Processing Software: Calibration and Stacking in Deep Sky Stacker, Levels/Curves/Enhancements in Photoshop CC
Support Files: 12 darks

 

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