Equipment - The William Optics Zenithstar 61ii small refractor scope

 New to this blog, then welcome, and after reading this post why not stop off here and find out more https://undersouthwestskies.blogspot.com/2025/01/welcome-to-my-new-astronomyastrophotogr.html

In today's blog, a 10 minute read, I, 

• review my Zenithstar 61ii refractor scope
• summarise its main features
• identify its advantages
• examine its disadvantages
• discuss who this scope is for 

Equipment: The Zenithstar 61ii small refractor by William Optics

I have owned this small refractor for just over a year and a half now and I thought it was time to review it. If you are considering a ‘beginner scope’ as part of a wide-field imaging set-up, then I hope the following observations will help you weigh up its pro’s and con’s when comparing it against other scopes you may be considering.  

 

My Zenithstar 61ii teamed up with an RVO 32mm Guidescope and the ASIair 120mm mini guide cam.

The mount is the skywatcher EQM-35-PRO; the camera an astro-modded Canon 800D.

Power to the mount and ASIair is supplied by the Celestron Lithium Pro power tank. 

What I like and have found good about the ZenithStar 61 II

1.      Features, Compactness & Portability

a.      Dimensions

                                                  i.      61 mm aperture and a focal length of 360 mm (f/5.9)

                                                ii.      Short 24 cm tube length, (around 315 mm with dew shield extended), 14cm height, (from bottom of mounting plate to top of ‘cat Series’ saddle handle) and 8.5 cm width

My Zenithstar 61ii wide-field rig

b.     Features

                                                  i.      The mounting rings have a ‘Cat Series’ saddle handle bar attached to the top of it which provides a Vixen-style mounting saddle for attaching things like a guidescope.

                                                ii.       The tension-adjustable, dual-speed rack and pinion focuser givers very smooth movement through its 75mm drawtube range and the focuser accepts 1.25- and 2-inch barrels, secured with compression rings

                                              iii.      A micro-focus knob with 1/10th speed adjustment for fine-focusing is so precise and a joy to use and the drawtube is ruled for repeat focus positioning.

                                               iv.      Built in Bahtinov mask which is part of the pull off cap – the lid unscrews to reveal the mask

                                                v.      Pull out dew shield extension which I put a dew band heater around

                                               vi.      I have a ‘love-hate relationship with the thermometer. Useful to monitor temperature for variations that may affect focus; morale sapping when its below freezing!

                                            vii.      Decent mounting dovetail bar

                                           viii.      Optional field flatteners – costing extra but worth the investment – I have the FLAT 61A

Bahtinov mask in-built to the scope cap

Note the rack/pinion control focuser, the dovetail on the clamp rings to hold the guidescope

The field flattener with M48 bayonet/thread adapter just visible in the camera

Also not the scale on the draw tube to help with back spacing. 

My ZS 61ii is really manageable and travel-friendly for astrophotography.  I’ve carried mine in a rucksack along with my star tracker and DSLR. In fact, it’s perfectly teamed with my Skywatcher Star Adventurer 2i tracker (although it did need an extra counterweight) and a perfect fit for my larger EQM-35-PRO mount. Portability – full marks!  I carry some eyepieces with me and a diagonal, so this scope is both my visual and astrophotography one on trips. I leave the field flattener permanently attached, along with the DSLR, so I rarely bother with using this scale.  By the way, I attach my DSLR to the flattener via a M48 screw/bayonet adapter.

 

Out in the field with my Zenithstar 61ii rig

2.      Good optics for its class

An air-spaced doublet with FPL-53 glass (a well-regarded glass type for apochromatic doublets). Various reviews in astronomy magazines such as BBC Sky At Night, report good colour correction. That review said “stars in the middle of the field ‘appeared sharp and bright’ and colour fringing was minimal for the Moon/planet tests”.  So, if you pair it with a camera suited to wide field, you can get pretty decent results without super heavy/expensive gear. Certainly, it works very well with my Canon 800D DSLR. It has an image circle ~ 45mm and I teamed it with a field flattener (FLAT61A) which has improved edge performance.

 

3.      Dedicated astrophotography intent & accessories

a.      Although it doesn’t come with them, I purchased optional dovetail saddles to mount on it – to hold a red dot finder and also my ASIasir mini. My son-in-law also 3 D printed a couple of spare saddles as well for me.

b.      If you want to do wide-field nebulae or star fields, the 360 mm focal length gives you a generous field of view. Stronger user feedback on forums shows people were using the ZS61 II with success for wide-field targets, guided setups, even narrowband imaging. I have used it for taking photos of the moon with some success – some good shots of lunar craters; its small aperture doesn’t collect a lot of blinding lunar light. I’ve used it with success on M45 Pleiades, M42 Orion Nebula, M33 Triangulum Galaxy, M31 Andromeda Galaxy just to name a few examples. Use telescopius.com and enter the scope, your camera and reducer details into the telescope simulator tool and then look at various targets to get an idea of what you will visualise/image with it.

c.      A quick search of Astrobin shows many fantastic images taken by astrophotographers of deep space objects. It has a proven track record. Because it’s used by many hobbyists, there’s a fair amount of discussion about spacing, flatteners, mounts etc on the popular astrophotography forums. That means useful advice is available for users.

 

Above: close up of the focuser, dovetail base bar, rings and handle

Below: side view showing guidescope (RVO 32mm F/4) and guidecam(ASIair 120mm mini); also ASIair mini on saddle screwed to optical tube assembly. Also visible is thermometer

4.      Looks quality built
What I am really impressed with is the build quality. Nothing feels compromised on it. It is a precision piece of engineering, well designed and well built. Truly functional and fit for its purpose. It just works straight off without any fiddling about.

Proof - it can be successfully used on a skywatcher star adventurer 2i tracker

So, lets turn to the dark side for a moment.

 What are the limitations (and what to watch out for)

Small aperture & moderate light-gathering

• With only 61 mm of aperture, you’re inherently limited in how much light can be captured compared with larger scopes (e.g., 100-120mm, 150mm or more). I struggle to do justice to faint deep-sky targets sometimes; an issue probably exacerbated by modest mounts and light-polluted skies). Let’s be realistic, it is optimized for wide-field, moderately bright targets (nebulae, clusters) more than very faint galaxies or ultra-deep exposures. I knew that when I purchased it

Edge performance / need for flattener

• While the optics in the centre are strong, without the optional field flattener, I read reviews and forum threads where people noted vignetting and distortion towards the edge of frame. On a full-frame camera set-up – you will need the optional field flattener if you want sharp stars right across the frame. I got it even for my APS-C crop camera. It did take a little bit of working out with my camera on ensuring that the spacing and back-focus spacing was correct but William Optics supplied a helpful leaflet explaining how to do this.

Mount & guiding requirements

• I’ll be frank here. On my tracker, the most I could get without guiding as an exposure was around 60” using this scope. 90” on a very good night. Anything over that and I was getting trailing. Polar alignment has to be extraordinarily accurate; your tripod very stable and you’re balancing really good! Team it with ASIair autoguiding and its awesome.

Potential for awkward positioning 

• In some setups, the focuser can be positioned awkwardly due to the dovetail bracket, requiring the telescope to be mounted upside down. I find it tricky when mounting it to my EQM-35-Pro mount – the focuser knob only just clears the mount side clamp by around a millimetre or so. You can see how close the focuser is to the ground in this image

when in my EQM-35-PRO mount, the mount clamp wall comes up to within a millimetre of the base of the silver focuser knob. Its a tight fit 

Less suitable for high magnification / planets / small targets

• With 360mm focal length and f/5.9, this isn’t designed for high magnification work (planets, lunar close‐ups) or very small targets requiring high resolution. So, not so good for planetary imaging or the really small deep sky objects.

Cost relative to aperture

• You pay for build quality and brand (William Optics). You could get larger apertures for similar money from other brands (though with different trade-offs). I often wonder if some William Optics products are overpriced – so when thinking about the Zenithstar – is the premium worth it for a small refractor or would it be better to get something else a little larger? I wouldn’t by the way always say that about all William Optics products – the RedCat series for example, are as far as I can ascertain, always very highly regarded as value for money by many astrophotographers.

Bottom line then, who this scope is really good for

• Someone like me, who wants a lightweight wide-field imaging setup (star tracker/ small mount) and wants decent results without hauling big gear. This is me – portability and compactness are key as I often take my astrophotography rigs with me on my travels in a small motorhome where payload considerations are at the forefront of my mind; and I walk out to some wild dark sky sites, having to carry all the gear in a big backpack.

• Someone, like me, who is happy to learn the craft and skills by focusing on nebulae, star-fields, Milky Way, large scale deep-sky rather than tiny galaxies or extremely faint fuzzies. In saying that I have managed to image several galaxies with some success.

• Someone who appreciates built‐in features like dual‐speed focuser, Bahtinov mask cap, good build quality, and is willing to spend a little extra (for flattener) for better performance.

 

Who should probably look elsewhere (or treat this as a secondary tool)

• If your goal is serious deep‐sky faint object work, very long subs, or large sensor full-frame with perfect corner stars and minimal aberrations without flattener. In that case, a larger aperture refractor/triplet or a dedicated astrograph might be more effective.

• If you plan planetary/high magnification work (Moon/planets) as your main focus — you’d benefit from a longer focal length or higher resolution optics.

• If budget is tight and you’re prioritizing aperture per £, you might consider alternatives that give you more light grabbing for same price (but maybe trade off portability/build/brand).

• If you prefer “plug and play” and don’t want to worry about flatteners, back-focus spacing, or corner distortion— then a bigger system might still require those, but the relative impact could be less.

 

Despite the rising moon, I take my chances when I get clear skies - here in the Sennen area of Cornwall 

The William Optics ZenithStar 61 II is a fascinating little wide-field refractor for astrophotography. I value its excellent portability, good optics for its size, and its wide field-of-view - perfect for nebulae and star clusters. It is a great ‘grab and go’ scope which I can set it up within minutes; for both visual and wide-field viewing and astrophotography. Compact and light is why it accompanies me on all my motorhome trips; it weighs 2.15kg. Just add a camera and you have a quality, easy-access imaging setup. It’s supplied with a padded carry-case, which is large enough to accommodate optional extras, such as the recommended field-flattener, but not a guide scope – which is a minor irritation.

Useful resources:

William Optics manual pages for zenithstar at https://support.williamoptics.com/products/zenithstar-61-ii

The videos below are ones that I found useful. I take no responsibility for their associated links etc.