William Optics Adjustable Flat6A III 0.8x Reducer / Flattener
William Optics Adjustable Flat6A III 0.8x Reducer / FlattenerWilliam Optics Adjustable Flat6A III 0.8x Reducer / FlattenerWilliam Optics Adjustable Flat6A III 0.8x Reducer / FlattenerWilliam Optics Adjustable Flat6A III 0.8x Reducer / Flattener

William Optics Adjustable Flat6A III 0.8x Reducer / Flattener

  (8 Reviews)
✓ 2 year warranty


4x in stock shipped 1-2 working days

About this product

Model:  wo_p-flat_6aiii
Part Number:  P-FLAT6AIII

Adjustable Reducer / Flattener for William Optics GT71, GT81, ZS103 Telescopes

This elegantly designed 2" reducer / flattener has been designed to optimise the flat-field imaging performance of William Optics f/6 to f/7.5 refractors.

Provides good illumination and a flat field across 97% of a full frame sensor field of view.

Attaches directly to telescopes with an M63 thread on the end of the focuser. 

Internal thread accepts 2" astronomy filters.

Requires an M48 threaded T-ring if using a DSLR camera.

Large Sensor Illumination 

  • Designed with nearly Full frame chip-size DSLR cameras in mind. 
  • FMC Triplet APO design.
  • Produced entirely with the best Ohara optical glasses. 


  • Reducing factor 0.8x.
  • Adjustable design, for perfect back focus it can be used with other models of refractor
  • 48mm filter ready

Superb Finish

  • William Optics usual high quality fit & finish.
  • All internal surfaces threaded and blackened to prevent reflections.

Easy to Use  

  • Will accept any standard 48mm T-ring for your camera.

Adjustable distance:

  • GT71 - 9.1mm
  • GT81 - 7.1mm
  • Z81 - 5.2mm
  • ZS103 - 2.5mm

Note: Not suitable for use with the William Optics V-power focuser which requires a flattener with 2" nosepiece (i.e FLat6a-II or FLat6a). 



Customer reviews

Average Rating (8 Reviews):  
Write a Review and share your opinions!

Rating (max 5):  
Classy Flattener/Reducer
08 September 2022  | 

I bought one for these for my f/6.8 WO 80mm EDII refractor. Fits perfectly and adjusted to required 5.2mm back focus. This is as usual, a solidly constructed, well designed accessory from WO. Thanks to Alex for the support from FLO.

Rating (max 5):  
William Optics Zenithstar 81 APO
14 May 2022  | 

perfect support from FLO, I originally ordered the wrong flattener, but in the end Chris advised me what would suit my camera, it was not a problem to cancel the order and create a new one. I highly recommend this store

Rating (max 5):  
Solid Item, Does the Job
26 April 2022  | 

The WO Adjustable Flat6A III 0.8x Reducer / Flattener is solidly built and has a graduated scale for accurate back focus adjustment. I use this on my GT71 with a WO Camera Rotator, this enables me to rotate the Camera Rotator, rather than the camera to adjust back focus. Just need to sort out some optical train tilt now but I wholeheartedly recommend this product.

Rating (max 5):  
Nice piece of hardware
23 January 2021  | 

Just got my GT71 with this flattener.
I made couple of shots this the telescope - amazing picture quality even compared with my 200mm reflector (and is not so demanding to the mount and guiding of course).
Didn't fit the flattener yet - I am confused with the numbers above - if one subtracts recommened adjustable distance from the backfocus distance from the table, one gets 53mm, not 55mm.
WO website has the different by this exact 2mm numbers. Probably this should be fixed?
I'm eager to test the whole setup next night anyway.

Rating (max 5):  
Perfect thing
28 October 2020  | 

Only minus - really hard to mount / dismount 2" filter inside

Rating (max 5):  
Excellent flattener
03 October 2020  | 

High quality gear and easily adjustable to get the correct spacing according to the OTA it is used on.

Rating (max 5):  
Space Grey
25 September 2020  | 

Pure quality as always from WO and great service from FLO, also it came in space grey as my scope is how lucky was I.

Rating (max 5):  
William Optics Adjustable Flat6A III 0.8x Reducer / Flattener
22 March 2020  | 

I have finally had the opportunity to try this out in combination with an older - Zenithstar -Williams 110 mm F 7.0 refractor. Connection required the M63 adapter nosepiece. The reducer/ flattener does an excellent job. Nice round stars right to the edge of a field that has increased just as expected for 0.8X reduction. FLO did an excellent job of sorting out the adapter problem (which I hadn't originally appreciated) and chasing it up for me as soon as it came available.


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