This is a "proper" 4" f/7 ED.

This is a used, minty, Pentax SDHF-105. D=105mm; F=700mm. The design consists of an SD doublet and a single field flatener mounted rearward in the OTA. The coatings are Pentax's legendary SMC. Though the design requires longer than a simple doublet to cool down, once at equilibrium it provides sharp, totally flat fields edge to edge with excellent contrast (no matter where Luna is near the edge of the FOV!).

Regards,

Jim