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

  (11 Reviews)
✓ 2 year warranty


6x 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. 

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 (11 Reviews):  
Write a Review and share your opinions!

Rating (max 5):  
Excellent service
Thursday, 1 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
Thursday, 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

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 2Ē 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.

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