The telescope manufacturer William Optics offers very high-quality apochromatic and achromatic refractors which are very well suited to visual observation, and especially to astrophotography.
William Optics
Adapter M63 Adaptors for Flattener Flat6AIII
$ 69.00
ready for shipping in 3-7
days
William Optics
Adapter Flat4 Draw Tube
$ 81.00
ready for shipping in 24
h