William Optics Zenithstar 73 III APO
William Optics Zenithstar 73 III APOWilliam Optics Zenithstar 73 III APOWilliam Optics Zenithstar 73 III APO
William Optics Zenithstar 73 III APOWilliam Optics Zenithstar 73 III APOWilliam Optics Zenithstar 73 III APO

William Optics Zenithstar 73 III APO

  (19 Reviews)
✓ 2 year warranty


1x in stock shipped 1-2 working days

About this product

Model:  wo_zs73_gd
Part Number:  A-Z73IIIGD

Latest V III model with CNC carry handle, Bahtinov focus mask & soft case (handle, mask & case not shown in photo). 

The NEW William Optics Zenithstar 73 APO III features an air-spaced doublet lens with fully multi-coated optics and an Ohara FPL-53 ED glass element for sharp, high-contrast images virtually free of false colour. 

It provides high-resolution images for astrophotography or wildlife photography and is a convenient ultra-portable telescope for visual astronomy (think binocular astronomy targets).  

Its fast f/5.9 focal ratio and compact size make it ideal for convenient wide-field astrophotography or piggybacking. 

CNC machined aluminium for a superior fit and finish. 

Dual speed 2.5" 1:10 R&P focuser.

Available in Blue, Red or Gold anodised.  

Supplied with mounting rings, CNC carry handle, Bahtinov mask, Vixen-style dovetail bar and soft case. 

NOTE: Photos show the earlier V2 model, which has a white focuser, the focuser fitted to the VIII model is the same but has a black finish.  

Ohara FPL-53 vs FPL-51 ED Glass

The dispersion properties of ED and SD glass elements are important in determining the overall colour correction. The abbe index is used to quantify the 'partial dispersion' of a particular glass. Pure Fluorite offers the highest partial dispersion at around 94.99 V; Ohara FPL-53 glass is very close to Fluorite at 94.93 V and is often referred to as Synthetic Fluorite.  FPL-53 is also noticeably better than Ohara's lower spec' FPL-51 glass which offers an abbe index of 81.54 V.

Field of View Simulator

What's in the box

  • Telescope OTA
  • Innovative Bahtinov Mask
  • Mounting Rings
  • CNC machined Carry Handle
  • Vixen-Style Dovetail
  • Soft Case


Aperture73 mm
Focal RatioF/5.9
Focal Length430 mm
Imaging Circle43 mm
Objective TypeED Doublet, Air Spaced,
Fully Multi-Coated, SMC coating.
Lens ShadeRetractable
Tube Diameter93mm (3.66")
Tube Length390 mm Fully Retracted
Tube Weight2.83 kg

Customer reviews

Average Rating (19 Reviews):  
Write a Review and share your opinions!

Rating (max 5):  
15 March 2023  | 

Seems like a top quality product. Not yet had the chance to test it however. FLO awesome company, top customer service.

Rating (max 5):  
A wee cracker
01 September 2022  | 

I was looking for a lightweight, optically excellent scope with a good quality focuser for use as a guide scope. This fits the bill on all counts. Nice quality, well presented and a fair price. Top quality advice from FLO regarding a suitable Baader ClickLock to suit it. Very happy with my purchase and my guiding has never been better (it is paired up with a Lodestar Pro)

Rating (max 5):  
WO 73ED 111
15 August 2022  | 

What a lil classy cracker the WO 73ED 111 is with its Superb focuser; havent done much AP with it just quick Planet shots with a DSLR, but visually superb for doubles with big fat Spurious Disks, with no flaring from diffraction rings as is the case with lesser or obstructed optics in average seeing.

GRS and Polar caps on Mars and the Syrtis already sighted at 9" with a barlowed 5mm Starguider EP...Cant wait to try the Tak 3.3 TOE in it!

Lovely contrast and very pinpoint stars compared to my C5 and better optically than my very good Fpl51 80ED..The smaller W.O. showing basically the same detail as the 80mm but a bit sharper and near zero C.A..That FPL53 glass makes a difference, a new kind of Clarity compared at mid/ high powers and exit pupils!
Worth getting for the Clarity on the Moon and Planets visually alone! Can only image what a great imaging OTA it will be.
I Reach for this now in average seeing, not worth bringing out the big guns this handles bad seeing... HIGHLY RECOMMENDED without reservations.

Rating (max 5):  
Quality telescope
18 July 2022  | 

Looks ,feels and performs like the quality product it is.

Rating (max 5):  
Great Quality
11 July 2022  | 

Thank you to FLO for going the extra mile to ensure I received the telescope while I was in the UK..really appreciate the fantastic service!
The telescope just screams quality! I would give the telescope 5 stars but I am struggling with the Z73R flattener/reducer which is still causing a lot of coma around the edges of my APS C sensor..I have followed the instructions but still facing issues so unfortunately, its dampening my experience with the telescope.

Rating (max 5):  
Beautifully manufactured!
15 March 2022  | 

Before I review the Williams Optics Zenithstar 73 III APO telescope, I want to provide a brief overview of my experience in purchasing from FLO. I received my first ever telescope and mount (an 8Ē Skywatcher Newtonian on an HEQ5 mount) almost twenty years ago. Over the years, as my knowledge and equipment has grown, I have, in the main, turned to FLO the majority of the time. Staff have always been prompt in answering any questions I may have and I really canít fault their service. Their staff are clearly knowledgeable, friendly and helpful.

Firstly, the Zenithstar 73 has been beautifully manufactured. The carry handle incorporates a finder-scope shoe which is very convenient- I have piggybacked my evoguide 50ED guidescope onto it very securely. The evoguideís green livery actually works well with the gold accents of the Zenithstar. I did not wish to damage the finish on the gold dovetail bar so I attached it to an ADM saddle, fixed to an eleven-inch dovetail bar. This helped with balancing since, with a DSLR camera attached, the telescope needs to sit forward, making the focuser lock screw otherwise difficult to access. Of course, the telescope can always be rotated 180 degrees so itís not a problem.

The coarse and fine focus adjustments are very smooth and the focus lock does its job well. My first views through the eyepiece really were very impressive. With such a wide field of view, the Pleiades (M45) filled a 15mm EP. Since my main interest is in astrophotography, I also purchased the 73A adjustable field flattener and DSLR-M48 ring adapter. Using a cropped sensor camera, the stars were pin-sharp across the entire frame; I could not be more pleased! This will be a great telescope for imaging large nebula DSOís and Andromeda. There is even a Bahtinov focusing mask built into the endcap and a thermometer in the focusing knob. It really is a well-designed instrument.

Rating (max 5):  
FLO recommended for solar
21 February 2022  | 

Bought to go with daystar quark & ZWO 174MM. I'm only new but & have limited skills but can see the image quality is superb. FLO recommended & im more than happy with the purchase

Rating (max 5):  
Superb optics
10 December 2021  | 

I was after a small portable scope for visual and occasional snaps. Previously I owned a Takahashi fs85q and a WO123 with LZOS glass. This diminutive refractor (weighs next to nothing) isnít far behind my other far more expensive scopes. Only managed visuals of the moon so far, but the detail is exquisite. Great optics.

Rating (max 5):  
Excellent service
01 July 2021  | 

Just purchased and had fast replys for advice beforehand ,arrived less than 48 hours later ,packaged safely and cannot fault Flo,any problems I know they will help out ,wont be the last time I use them,thanks

Rating (max 5):  
Great scope
17 June 2021  | 

This was my first step up from camera lenses. I did a lot of review reading and opted for WO because of optical properties for Astrophotography, built quality and yes, looks. The scope didnít disappoint. Itís a pleasure to assemble and very satisfying to hold and use. The CNC carry handle is particularly helpful and provides confidence that you wonít drop the thing. It is quite heavy and my Star Adventurer just about manages. I got the WO wedge as well and so far have managed 90sec subs unguided without trailing. My next upgrade will be here towards a more substantial mount.
One quirk: The built-in Bahtinov mask works a treat in combination with the solid focusser and, once fixed, appears to hold focus for ever. I just check every time between sessions and itís still spot on. Such a difference from the fumbling micro-turns with my Nikon lens. However, unscrewing the mask cover from the nicely machined lens cap takes about fifty turns and is surprisingly noisy so all your neighbours and local foxes will be aware that you are at it againÖ The cap itself attaches like silk to the dew shield.

The scope out of the box is not set up for photography. You either need the flattener or other spacers and extra adapter if using DSLR. I chose the recommended bundle and, as FLO stated, the Zenithstar was available in stock (I think the last one in the UK at the time!) but the flattener would take a few weeks due to the Suez crisis and manufacturing delays. I bought a simple 40mm spacer to bridge that time and I wouldnít bother buying this scope without field flattener. This comes at a hefty price but without it chromatic aberration anywhere from dead centre is atrocious and stars near the edge look like smeared out flies on a windscreen. However, FLO clearly state this in the description so no points deducted. Because the flattener is WO with the same built quality it just completes the whole assembly and WO should probably sell it like that from the start
So far I canít say anything negative and yes, it did arrive with three weeks of cloud cover

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