Free Shipping On Many Items

The Telescope Authority
Since 1947

View Shopping Cart

Your Cart is Empty

William Optics FLAT6AIII Adjustable Field Flattener


- Read
  • Free Shipping

  • More on the Way in 14 - 28 Days

Add to Wishlist

Got questions? Click for live chat

  • Refine your flat-field performance.
  • Fully multi-coated Ohara glass optics.
  • Reducing factor: 0.8X.

Product Details

  • The William Optics Adjustable Field Flattener improves the flat-field imaging performance of William Optics GT71, GT81, Z81, and Z103 refractors. 

    Features of the William Optics Adjustable Field Flattener

    • APO triplet optics made with Ohara glass. 
    • Fully multi-coated to provide bright and flat field across 97% of full-frame sensors.
    • Built with M63 threads on the telescope side.


    The following telescope models can be used with the William Optics FLAT6AIII Adjustable Field Flattener

    • Amount of Adjustment:
    • GT71 - 9.1mm
    • GT71 - 9.1mm
    • GT81 - 7.1mm
    • Z103 - 2.5mm
    • Z81 - 5.2mm
    • Back Focus:
    • GT71 - 64.1mm
    • GT71 - 9.1mm
    • GT81 - 62.1mm
    • Z103 - 57.5mm
    • Z81 - 60.2mm
    • Image Circle:
    • GT71 - 44mm
    • GT71 - 9.1mm
    • GT81 - 44mm
    • Z103 - 43mm
    • Z81 - 44mm
  • specifications

    Free ShippingYes
  • included items

    • Refine your flat-field performance.
    • Fully multi-coated Ohara glass optics.
    • Reducing factor: 0.8X.

Product Reviews

Customer Reviews
4.5 Based on 4 Reviews
5 ★
4 ★
3 ★
2 ★
1 ★
Customer Photos
Write a Review Ask a Question

Thank you for submitting a review!

Your input is very much appreciated. Share it with your friends so they can enjoy it too!

Filter Reviews:
  • flattener
  • edges
  • William
  • frames
  • deal
  • difference
  • view
  • field of view
  • Glass
  • weight
Gregory T.
United States United States


Love this little device so much I've bought it for 3 telescopes, GT71, Z81, and Z103. I also bought the FLAT61R flattener which includes a rotator.

Chris W.
United States United States

William Optics Flat6Alll adjustable field flattener

I bought this flattener for my GT71 because it is recommended by William optics for that scope to reduce elongated stars around the edges of the field of view. I tried using the scope without it but that just was no good. The flattener arrived quickly, thanks to OPT’s excellent shipping department, and it was no problem at all to mount to the scope. I was up and running in no time and man what a difference it made. The entire field of view is nice and flat all the way to the very edges of the frames with zero elongated stars. It did add quite a bit of weight to the scope though, because it has legit glass in it. I had to change the total balance of the scope so it would work, which really wasn’t that big of a deal. Overall, excellent product, excellent service, and excellent quality from OPT and William Optics.

OPT Telescopes William Optics FLAT6AIII Adjustable Field Flattener ReviewOPT Telescopes William Optics FLAT6AIII Adjustable Field Flattener Review
Natalie A.
United States United States

High Quality, low quality for the user’s knowledge

I’m posting a review after getting an email. Fast shipping, I appreciate receiving this, but I’m a complete newbie at all this! I still can’t see anything as everything looks like the bokeh effect, everything looks like colored circles. It would be nice if the brand could include a user guide, even a tiny card that can direct us to an online user guide. I’m using my DSLR’s viewfinder and taking photos as my view piece. I even tried using another DSLR to see if my view changes. I may buy the diagonal in the future because it’s a little disappointing I couldn’t see anything despite looking at all the telescope’s contents. Perhaps when it’s warmer I’ll try to figure it out better.

Stephen T.
United States United States

Field Flattener

Works great with my zenith star 81