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Sky-Watcher Evoguide 50ED Vs William Optics Redcat Z51 For Wide Field Astrophotography

This is the second and last part of my detailed hands-on review of the Sky-Watcher Evoguide 50ED.

In part one, I presented this scope and the many ways it can be used.

Now, it is time to answer the questions that keep astrophotographers on a budget like myself awake at night (at least during the cloudy ones :P): is the Evoguide 50ED any good at wide-field astrophotography? Can it be a valid budget alternative to the William Optics Redcat?

Ready? Let’s go!

compare the evoguide 50ed to the redcat 51 for wide-field astro imaging

What Makes A Scope A Good Imaging Scope?

Before going at the heart of this article, let’s try to define what makes a scope a good imaging scope.

One way to answer this question is to go by the numbers: larger apertures are better than smaller ones, and fast scopes are better than slow ones.

But those two considerations aside, there is nothing else we can say that is true and general in absolute. 

You could easily object that it is a fact that apochromatic refractors are much better at astrophotography than achromatic ones. That’s true but, maybe, I don’t want a refractor, thus I don’t care about this.

This brings me to the second way of answering that question: the subjective way. 

While we are all after getting nice images of the many wonders of the Universe, personal choices, opportunities, and personal skills put us on different paths and strategies.

Astrophotography is a game. The goal is set: create nice images, but the path that leads you there is not. You have to decide what works best for you and which road to take. And sometimes, to win, you have to think out of the box.

Astrophotography is like a game
Astrophotography is a wonderful and addicting game and you have to find your way through it. 

The telescope design, its focal length, the available accessories, are more a matter of personal preferences and opportunities than absolute truths.

Say you are a beginner. You have to travel to a distant location to find a decent dark sky. You are on a tight budget. Or, maybe, you are an occasional star shooter. 

In these cases, the best scope for you is probably not going to be the hardcore deep-sky astrophotographer’s dream scope.

And the same is true for the camera, the mount, and almost any other piece of equipment.

Guiding Scope As Imaging Scope: Yay or Nay?

With the idea of finding the absolute best telescope out of the way, we can look at the many good looking and affordable guiding scopes with an aperture and a focal length that are suitable for wide-field astrophotography and ask ourselves:

“can we consider a guiding scope to be a good imaging scope for beginners, astrophotographers on a budget and/or on the move?” 

Orion 60mm Guide Scope

Compared to the Evoguide, the Orion Guide Scope has a larger 60mm aperture and it features a telescopic draw tube combined with a helical focuser for quick and precise focusing.

The general consensus is: no, we cannot; we should not! 

Sadly for us, naysayers seem to be right, but are they?

Their reasoning is sound: why should anyone bother with using high-quality ED glass in a guiding scope?

Why should anyone go through the trouble of correcting a guiding scope’s strong field curvature and adding a precise and easy to operate focuser, when all people need from it are decent enough stars at the center of the frame in order to successfully guide their imaging equipment?

ZWO Miniscope 30-F4 showing strong field curvature and chromatic aberration
The ZWO Miniscope 30 F4 is a great miniscope for guiding, but the strong field curvature, strong chromatic aberration, and clumsy focuser makes it a bad scope for imaging.

Enters Sky-Watcher. 

With the idea of creating, perhaps, the ultimate guiding scope, Sky-Watcher leaped forward and released its Evoguide 50ED

Sky-Watcher Evoguide 50ED
My copy of the Sky-Watcher Evoguide 50ED.

The Evoguide 50ED is a guiding scope that effectively is an apochromatic doublet refractor, featuring a precise helical focuser.

Officially, the added goodies are there to give you tighter stars for superior guiding capabilities. But they also make the Evoguide 50ED a rather expensive guiding scope. 

On the other hand, should the Evoguide perform well for wide-field astrophotography, it would definitely be an affordable and interesting option.

And, maybe, even challenging his Majesty, the William Optics Redacat Z51. 

The mind runs wild, and the game is on!


The Champion: William Optics Redcat / Spacecat Z51

William Optics Redcat is now called Spacecat
The most recent version of the William Optics Redcat is now called Spacecat and is available in Gray. It is a Redcat with a different color, nothing else changes.

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Tech Specs

Lens diameter: 51mm | Focal length: 250mm | Aperture Ratio: f/4.9 | Max useful magnification: 102x | Optical Design: Petzval Quadruplet | Glass types: Ohara FPL53 and FPL51 | Field Corrector: Integrated | Illuminated and corrected field: 44mm (diameter) | Backfocus: 59.5mm | Camera connection: M48x0.75 thread | Additional thread: M56x0.75 | Filter size: 2” | Focuser: Helical | Camera 360º Rotation: Yes | Base plate: Vixen and Arca-Swiss compatible | Tube length: 225mm | Tube weight: 1.5kg | Tube material: Aluminium | Included accessories: bahtinov mask, carry case.

Being a high-quality quadruplet with a petzval design, lightweight, compact, and compatible with a wide range of accessories, it is not surprising the William Optics Redcat is so popular and, arguably, the scope of reference for wide-field astrophotography.

All these goodies, though, comes at a price… and a rather steep one too.


The Challenger:  SkyWatcher Evoguide 50ED

The latest Sky-Watcher Evoguide 50ED comes with also a green dovetail for easy mounting.

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Tech Specs

Lens diameter: 50mm | Focal length: 242mm | Aperture Ratio: f/4.8 | Max useful magnification: 100x | Optical Design: Doublet | Glass types: Ohara S-FPL53 | Field Corrector: Available as accessory | Backfocus: 60mm | Camera connection: M48x0.75 thread or 1.25” nosepiece | Filter size: 1.25” | Focuser: Helical | Camera 360º Rotation: Yes, (nosepiece only) | Base plate: Vixen compatible | Connection to telescope: Bracket for standard finder shoe | Tube length: 220mm (260mm with extender) | Tube weight: 865gr | Tube material: Aluminium | Included accessories: 40mm extender, stop ring for 1.25” eyepiece, collimation rings.

The Evoguide 50ED is a guiding scope on steroids: it features two (some says one) Ohara S-FPL53 ED lenses to remove chromatic aberrations, has a precise helical focuser, it can take 1.25” eyepieces, and can also be used as a grab ‘n’ go wide-field telescope. 

With the standard T2 thread, you can easily mount on it your DSLR or mirrorless camera.


Features Face-To-Face

William Optics Redcat Z51 compared to the Sky-Watcher Evoguide 50ED
The William Optics Redcat Z51 (left) compared to the Sky-Watcher Evoguide 50ED (right).

Price

For a little more than ⅓ the price of the Redcat, the Evoguide 50ED looks like a real bargain, even when adding the cost of the much needed field flattener.

The Evoguide wins hands down here.

Standout Features

The Evoguide stands out because of the Ohara glass lenses it uses. The focuser is smooth and nice, but there are other guiding scopes out there offering a helical focuser.

For the Redcat, the optical scheme is what makes this scope the reference in the world of wide-field telescopes. Being a quadruplet with a petzval design, it naturally removes not only the chromatic aberrations but also the field curvature of the instrument.

At first, many telescopes seem to be much more affordable than the Redcat, but they need a costly dedicated field flattener to be usable for deep sky astrophotography. 

With the Redcat, you don’t need anything else.

Redcat clearly wins this one.

Build Quality

Both scopes are very well made, with the body in aluminum and smooth focuser.

Personally, I don’t like to mount a scope for imaging with the classic collimation rings used for guiding scopes, as I feel the ensemble is not that sturdy. I prefer the Redcat solution here.

The Redcat rubberized focusing ring is a nice touch over the metallic one of the Evoguide. I also like the possibility offered by the Redcat of precisely rotating the camera for better framing and composition (particularly for mosaics).

Build quality is a close call, but I give a slight advantage to the Redcat.

Image Quality

In absolute terms, when it comes to image quality, the Redcat should be the clear winner: it is a quadruplet Vs a doublet, and it also corrects the field curvature without the need for extra gear.

I don’t have the Redcat, but from what I can see on astrobin, this scope delivers very nice images. Not being myself addicted to pixel peeping, the feeling I get is that image quality is up with expectations.

astrophotography images taken with the William Optics Redcat
Some astrophotography images taken with the William Optics Redcat. (Image Source: Astrobin)

Yet, on the internet, there are some complaints about the quality of the field curvature corrections, but I would hardly consider this to be a deal breaker for most of us.

So, where does the Evoguide stand on this? Can this guiding scope deliver astrophotography images of high enough quality?

What Sort Of Images Can I Expect From The Evoguide 50ED?

To answer those questions, let’s discuss the different types of astrophotography you can do with the Evoguide 50ED and its results.

Lunar, Solar, And Planetary Astrophotography

Field curvature is not a real problem in this type of photography, and the Evoguide performs really well. 

Sure, the aperture is small and there are photographic lenses with longer focal length and larger lens diameter, so: why bother with the Evoguide at all? 

The reason is that because of its smooth helical focusing, it is extremely easy to nail the focus and obtain sharp images. With in-camera image stabilization, it is not difficult to snap good moon shots handheld with the Evoguide.

Single shot of Moon taken with Olympus E-PL6 micro four thirds mirrorless camera
The Moon. Single shot with Olympus E-PL6 micro four-thirds mirrorless camera, handheld.

Finally, with less glass than a typical photographic lens, the Evoguide is lighter and faster than most equivalent telephoto lenses and it often delivers images of better quality. 

Thanks to the Ohara glass lenses, it is difficult to have color fringing around the Moon.

The scope is so easy to use and quick to set up that it is not a problem to experiment with it and the Moon.

Moon composite to show the Earthshine
My first composite to show the Earthshine. Evoguide with  Olympus E-PL6 micro four-thirds mirrorless camera.

With a white light solar filter, you can also use the Evoguide for solar photography with some interesting results, particularly on cloudy days.

solar filter used to capture sun and clouds
Sun’ n’ Clouds. Single shot, Evoguide 50ED with Olympus OM-D EM-5 Mk ii and solar filter.

A few days ago, I was even able to use my Evoguide to photograph the sunspot 2776, one of the first in this new Solar Cycle. While being as large as the Earth, with the Evoguide this sunspot is little more than a speck, but is still nice to see.

Sunspot 2776 taken with the evoguide 50ed
The Sunspot 2776 on October 19th, 2020. Single shot Evoguide 50ED and Olympus OM-D EM-5 Mk ii with solar filter, handheld.

Thanks to the maximum usable magnification of about 100x, by pairing a planetary camera with a 2x barlow lens, you can get some decent images of Jupiter and Saturn.

Jupiter with two of its 4 major moons and Saturn
Jupiter with two of its 4 major moons (left) and Saturn. Evoguide 50ED with ASI224MC and Celestron X-Cel LX 2X barlow lens on Sky-Watcher Az-GTI mount.

All in all, this scope is great for casual lunar and solar astrophotography with your DSLR or mirrorless camera. I anticipate the Evoguide will be a great scope to photograph lunar and solar eclipses, as well as the transit of Mercury or Venus in front of the Sun.

Jupiter and Saturn are also within the reach of the Evoguide 50ED, both for photography and visual observation.

Deep Sky Astrophotography

NOTE: To be as objective as I can (particularly since I still suck at the editing), I have only stacked, calibrated, and auto-stretched in Astro Pixels Processor my deep sky images. I didn’t go further with editing the images and have not cropped them.

The Evoguide is, well, a guiding scope. 

While the Ohara glass lenses do a pretty good job in suppressing halos and purple fringing around the stars, field curvature is extreme.

The first target I tested the Evoguide with was Andromeda, using my Olympus E-PL6 micro four-thirds mirrorless camera. 

Since the camera has a micro four-thirds sensor, which is smaller than an APS-C one, I thought I could get rid of the negative effects of the field curvature by cropping out a little bit the borders of the frame.

No big deal. But I was wrong…

Andromeda taken with Evoguide 50ED with Olympus E-PL6
Andromeda. Evoguide 50ED with Olympus E-PL6 and filter Optolong L-PRO on Sky-Watcher Star Adventurer PRO, unguided.

The field curvature is visible as elongated stars and a steep drop in sharpness in the entire frame but the very center.

Even with my ZWO ASI183MC camera and its small 1”-sensor, I was not immune to field curvature. 

Sadr’s Region in Cygnus
The Sadr’s Region, in Cygnus. ASI183MC on Evoguide 50ED, filter Optolong L-PRO, on Sky-Watcher Star Adventurer PRO, guided. 

At this point, I must be honest here: it seems thatout of the box, the Evoguide is only good for snap Moon and Sun images with your DSLR or mirrorless.

Bummer, because the images look very promising to me. If only we could flatten the field …

Luckily, at the time of this article, there are two field flatteners we can use with the Evoguide for improving the image quality of the scope for deep sky astrophotography: the Starizona EVO-FF and the Sky-Watcher Evoguide 50ED Field Flattener.


Starizona EVO-FF Field Flattener For Short Focal Refractors

With the Starizona EVO-FF field flattener, developed specifically for being used with short focal refractors, the Evoguide begins to shine!

Starizona EVO-FF Field Flattener
The Starizona EVO-FF Field Flattener for short focal refractors.

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Pros

  • Compact
  • Lightweight
  • Uses 2 elements optics, fully multicoated
  • Has a 34mm backfocus on the Evoguide with a 2mm tolerance
  • Suitable for mirrorless cameras and cooled/uncooled astro cameras
  • Flat field up to APS-C sensor size (Image circle 27mm)
  • Can take some filter wheel when used with monochrome astro cameras
  • Can work with different scopes

Cons

  • Expensive
  • Not enough backfocus for using with a DSLR camera
  • No T2 thread for rigid connection to the scope
Images taken with the Evoguide 50ED and the Starizona EVO-FF field flattener
Images taken with the Evoguide 50ED and the Starizona EVO-FF field flattener. (Image Source: Starizona).

The EVO-FF is not specific to the Evoguide, but it is suitable for refractors with focal lengths from 250mm to 450mm, with a backfocus ranging from 34mm to 21mm.

For using the EVO-FF on the Evoguide, simply remove the 40mm extender and insert the flattener via its 1.25” nosepiece. Lock it well in position with the thumbscrews. The nosepiece is threaded for easy use of 1.25” filters.


Evoguide 50ED Field Flattener

Very recently, Sky-Watcher decided to produce its own field flattener for this scope: the Evoguide 50ED Field Flattener, and this is what I personally use.

Sky-Watcher Evoguide 50ED Field Flattener
The new Sky-Watcher Evoguide 50ED Field Flattener.

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Pros

  • Compact and Lightweight
  • Affordable
  • Can be threaded on the T2 back of the Evoguide
  • Can be used with a 1.25” nosepiece (not included)
  • Comes with aluminum front and rear caps
  • Uses 2 elements optics, fully multicoated
  • Flat field up to APS-C sensor size

Cons

  • Short backfocus of 17.5mm
  • Can’t be used with DSLR, nor mirrorless cameras
  • Cannot take a filter wheel
  • It is unclear if it can perform well on different scopes

Please note that both the Starizona EVO-FF and the Sky-Watcher Evoguide 50 ED Field Flattener do not reduce the focal length of the Evoguide.

Living in Belgium, October is not the best month for astrophotography, as it is often cloudy. Still, I did have the chance to use my Evoguide with the Evoguide 50ED Field Flattener, and personally, I found the image quality to be very promising, particularly for the money.

Pacman Nebula taken with Evoguide 50ED + Evoguide 50ED Field Flattener
The Pacman Nebula. Evoguide 50ED + Evoguide 50ED Field Flattener with ASI183MC and filter Optolong L-Enhance on Sky-Watcher Star Adventurer PRO, guided.

Let’s see this image in a bit more detail, by considering 100% crops of a region near a corner of the frame and near the center.

Stars are nicely round (for what 4 minutes long exposures on the star adventurer allows), and the little residual chromatic aberration can probably be further reduced with a more accurate focus.

close up details of image taken with evoguide 50ed
100% crops from the previous image taken with the Evoguide 50ED Field Flattener.

The Evoguide 50ED: A Great Little Imaging Scope For Some, But Not For All

If you are looking for a compact and portable scope for wide-field astrophotography, maybe to pair to your Sky-Watcher Star Adventurer Pro or other star trackers, by now you may be sold.

With a dedicated field flattener, the Evoguide looks like it is capable of delivering very good deep-sky images, but this scope is NOT for everyone.

I live in an apartment in Brussels: I lack the space to store and set up a large scope and a heavy-duty equatorial mount. And I can’t see enough sky to justify the cost for such a setup. 

For my astrophotography, I need to move away from the city and this is why I decided to settle with my Star Adventurer. 

But, wanting to improve my deep-sky astrophotography, I gambled that for the money it was better to go with the Evoguide plus flattener and uncooled ZWO ASI183MC camera, rather than buy the Redcat and be stuck with my stock Olympus camera.

All in all, I think I made the right call for my needs. 

What Camera Can I Use With The Evoguide?

While the scope can be used with a DSLR camera, once you put the field flattener in, you don’t have enough backfocus left to achieve focus with your DSLR.

At the time of this article, of the two available field flatteners, only the Starizona EVO-FF allows you to focus with a mirrorless camera, thanks to its backfocus of 34mm.

The Sky-Watcher Evoguide 50ED Field Flattener, instead, has only 17.5mm of backfocus, barely enough to reach focus with cooled and uncooled astro cameras.

So, no DSLRs with the Evoguide and at the moment, there is no way around this. At best, you can use a cropped sensor, mirrorless camera.

Because of their short focal length, both the Evoguide and the Redcat work best with cameras having a relatively small pixel size, such as the ASI183MM/MC. 

You can calculate the optical resolution for your setup with this Astronomy Tools calculator. 

What Filters Can I Use With The Evoguide?

You can only use 1.25” filters, either screwed on a nosepiece or with a low profile T2-1.25” adapter like those provided by ZWO for their cameras.

If you already have a set of 2” filters and don’t want to buy smaller ones, then the Evoguide is not for you.

If you shoot narrowband, you need a filter wheel. The Starizona EVO-FF has enough backfocus to let you use some combinations of filter wheel and cooled/uncooled monochrome astro cameras.

With the Sky-Watcher Evoguide 50ED Field Flattener, I’m pretty sure you cannot use a filter wheel.

What Mount Do I Need For Imaging With The Evoguide?

Telescopes like the Sky-Watcher Evostar 72ED can be used on a tracker, but they really are better suited for larger mounts.

Instead, the Evoguide 50ED weighing only 865gm can comfortably sit on a tracker like the Sky-Watcher Star Adventurer PRO, with room to spare for more equipment.

ultimate deep sky astrophotography setup with star adventurer pro
My ultimate deep sky astrophotography setup, built around my Sky-Watcher Star Adventurer PRO.

With The Evoguide, Do I Need To Guide My Mount?

If the weight of the scope is not a problem even for a star tracker, with a focal length of 242mm, you may want to guide your mount for best performances.

I guide my Star Adventurer Pro with the ZWO MiniScope 30 F4 and a ZWO ASI224MC and the whole setup weighs less than 2kg, well within the acceptable limits for doing astrophotography.

While mounting a guiding scope over the William Optics Redcat is a no brainer, with the Evoguide you need something different than the collimation rings it comes with. One does not usually guide a guiding scope…

These 3D printed brackets from Astrokraken are specifically made for using the Evoguide as an imaging scope. By providing a standard finding shoe mount, it is now easy to add a mini guiding scope on top of your Evoguide. 

Olympus OM-D EM-5 Mk ii connected to the Evoguide
My Evoguide is mounted on the Astrokraken Brackets. Note the classic shoe mount for guiding scope at the top of the assembly, as well the attachment for a classic red dot star finder.

Other solutions may be found as well, you just need to be creative. 

A Video Recap

Here is a video I made about using the Evoguide 50ED for astrophotography. Showing the different types of setups for doing eyepiece projection, prime focus with a DSLR or Mirrorless camera, use of a planetary camera, and finally, the use of the Evoguide 50ED Field Flattener with astro camera for deep sky astrophotography.

Conclusion

The Sky-Watcher Evoguide 50ED is an amazing guiding scope that can double as a daylight telephoto lens for your DSLR or mirrorless camera, as a spotting scope, as a finder scope and as a portable wide-field telescope.

Observing the Moon in Brussels
Observing the Moon and Jupiter grazing the Brussels’ rooftops in a hazed night. iPhone over a Celestron OMNI 32mm Plöss eyepiece.

You can photograph the Moon, the Sun, and the Planet with it. And, with a dedicated flattener, the Evoguide 50ED is capable of delivering great deep-sky images.

All this for a fraction of the cost of the William Optics Redcat Z51. But …

To take full advantage of the Evoguide, you need to accept its limits:

  1. You cannot use a DSLR for deep sky astrophotography.
  2. If you have a mirrorless, you have to buy the more expensive Starizona EvoFF flattener instead of the more affordable one from Sky-Watcher.
  3. You cannot use 2” filters.

If you cannot work around its limits, then the Evoguide is not the right instrument for you, and you should look elsewhere.

But if you can deal with those limits, then the Evoguide is a valid, budget alternative to the William Optics Redcat Z51 and other short focal refractors. 

Particularly so if you are already planning to move away from your DSLR and get a dedicated astro camera.

To conclude, let me show you what I think is hands-down my best DSO image so far. Can you guess what scope I was using? 😉

The Pac-Man Nebula in Ha and OIII
The Pac-Man Nebula in Ha and OIII.
About Andrea Minoia

Andrea Minoia works as a researcher in a Belgian university by day and is a keen amateur astrophotographer by night.

He is most interested in deep sky photography with low budget equipment and in helping beginners along their journey under the stars.