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

  (9 Reviews)
✓ 2 year warranty


Out of stock due 10-15 working days

About this product

Model:  wo_zs73_gd
Part Number:  A-Z73IIGD

Latest V III model with CNC carry handle and Bahtinov focus mask (handle and mask 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. 

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

It's fast f/5.9 focal ratio and compact size makes 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 (9 Reviews):  
Write a Review and share your opinions!

Rating (max 5):  
Order and receiving items
Thursday, 18 March 2021  | 

What a pleasure it is to have FLO and staff to available to discuss technical queries and order items with complete confidence. The William Optics Z73 is a quality piece of engineering and along with the field flattener, I'm looking forward to making the next step with the quality of my astrophotography images. Ordered on Thursday morning, received in Switzerland 2:30pm the next day. Amazing Thank you so much

Rating (max 5):  
Awesome scope
Tuesday, 12 January 2021  | 

The first thing you recognise about this scope on opening, is just how well built this piece of kit is. It looks fantastic, I got the gold version, but imagine that any colour would be just as good. I have added this to piggyback on my Celestron C11, an its a great choice, with now having the option of a widefiled scope or high magnification, so feel I have a great mix now.

I have used this with my Atik infinity camera, and it has given great wide field views og M42 and for the first time to be able to get M31 into full frame view.

My only difficulty has been getting focus for visual observation, as I did not purchase the focal reducer, which is primarily for DSLR camera and as I was not using this decided not to purchase. I have been able to focus using the diagonal from my C11, although will still look to resolve this to use a straight through eyepiece longer term, as being piggy-backed on the C11, subject to the angle of an object, its not that easy to get your eye in, but that's my issue nothing to do with the scope.

It will also allow me, when Covid travel restrictions are lifted, to have a great scope to head off to darker sky areas, which I expected, from my experience under Bortle 8 skies the views will be awesome.

This is truly an exceptional scope for the price and very please with this purchase.

As always, great service from FLO, who have been very helpful when selecting items, so thanks guys.

Rating (max 5):  
Excellent quality
Friday, 4 December 2020  | 

I've had a chance to use the scope and the quality is really good. Everything is metal and has a real good feel. With the flattener the stars are good all the way to the edge. What is a little confusing is how you get the flattener on at first. it's not clear if you need to undo any screws or how to remove the optical piece. But I undid the three small screws and then you can unscrew the whole piece, quite simple once you know.

What is also unfortunate is the soft carry case. It's perfect if you only use the scope as delivered but if you want to attach the handle for a finderscope, guidescope or use a flattener the scope will no longer fit in the case. So each night you're out you have to redo and undo everything to use the case.

Just some good practical things to know. I'm very pleased with the scope itself.

Rating (max 5):  
above expectations
Tuesday, 3 November 2020  | 

Bought this scope as my second telescope upgrade. First was the evostar 72ED. The Zenithstars 73 first light subs look very good. Sharp stars and almost no chromatic aberration. A big plus compared to my first semi apo refractor.

Rating (max 5):  
Cracking little scope
Thursday, 29 October 2020  | 

Bought this with a WO adjustable flattener and am not disappointed. I was originally going for a RedCat51 but as they are out of stock worldwide decided to try one of these instead. I am so pleased I did, what a fantastic little scope, beautiful finish and amazing image first night out. I am using it with a ZWO EAF, fits perfectly and I now have a fully portable wide FOV lightweight rig as my big Edge HD rig is just too heavy to carry about. I put in on my old AVX and the payload is fine as it was guiding through my OAG well. I stick my ASI294 Pro image train on it with a Optolong Pro filter. Fantastic results even with a nearly full moon. Well done William Optics for the quality (and FLO for the price and service). As I live in Spain, no clouds came with the package despite the new FLO stickers warning me ha ha!

Rating (max 5):  
Wednesday, 28 October 2020  | 

Stunning scope that is a work of art. Great service from FLO 😁

Rating (max 5):  
Great scope with some points of attention
Tuesday, 14 July 2020  | 

Nice scope to work with. Though there are a few minor points I encountered. The fancy temperature gauge is off by 3 degrees celcius (why?!). When using a dslr, no declination balance can be achieved, because de dovetail cannot move further back because of the focuslock screw (need a secondary dovetailbar or spacerblocks for the scoperings). I added metal washers to the dovetail bolts, since the bolts left impressions in the metal (no overtightening). I like the built-in bahtinov mask. The focuser is precise and smooth, love it! The gold colour tends to be more towards orange (compared to the photos and older WilliamOptics). The WO73flattner I ordered together has a matching colour. Last point since the flattener is screwed into the scope, changing to visual you need to unscrew the flattener, re-attach the original scope part, then you can connect the WO dielectric diagonal, and then you can use your eyepieces. A slide in 2 flattener is easier. I am happy with the scope, despite these points mentioned (okay, the temperature gauge is disappointing)

Rating (max 5):  
Monday, 11 November 2019  | 

First one received was faulty but FLO were great and shipped the replacement before I had even returned the faulty one.

Build quality is superb, this replaced and ED72 and things like the focuser are in a different league. Used in combination with the ZS73 flattener the field is perfect from corner to corner.

Rating (max 5):  
Monday, 24 June 2019  | 

I purchased this from FLO earlier this year to go with my Star Adventurer mount (also FLO) and a Manfrotto photo tripod. Initially I thought it was going to be too heavy especially with a Nikon DSLR (APS) mounted but the mount chugged along nicely. The optics on the ZS 73 APO are really nice just managing to the corners on my D5100 but falling off with the FX chipped 800E. I then purchased it's Flat 73A adjustable flattener (not FLO) and the difference in field flatness was very marked even with the FX sensor. The flattener is x1 so no changes in FoV to contend with. I have been taking mono photos with the D5100 up to about 3 mins which is about the best I can get from the Star Adventurer. It's a great visual scope too. Paired with my ES 68 and 82 eyepieces the views are better than I ever expected. I took the ZS-73 up to the Lake District under some better skies than I usually deal with - what a treat.


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