https://takahashi-europe.com/catalog...-flattener-toa
The 67 flattener is an essential accessory for imaging and is a top piece of glass. A 90mm image circle is huge and means it won't contribute to vignetting even with the larger chips. Includes generous back focus (106.2mm).
Works with other triplet refractors out there: eg SW, AP, APMs etc. Some have also used these on RCs.
Includes the standard Tak box and 2x Tak spacers/adapters.
$625 plus shipping or Cbr/Syd pickup.