Airy Disk 0.75x Flat-field Adapter

3 element – 0.75x-Flat Field for sharper stars all to way to the edge. Specifically made for the 106mm APO. Screws on to the M63x1-Thread. 0.75x factor – reduces the focal length to 525mm while giving f/4.95. 55 mm to 60 mm back distance – fine tune in 0.05 mm Increments – from the M48x0.75-thread.