Review of the Askar 72mm f/5.6 Quintuplet Petzval Flat-Field Astrograph and Askar 0.7x Reducer
1. Overview
Many vendors offer premium small triplet refractors for visual use and astrophotography. An ED or apochromatic objective, a relatively fast focal ratio around f/6, and a rotatable two-speed focuser are standard fare, and an optional field flattener facilitates imaging with larger APS-C and full-frame sensors. The new ASKAR FRA400 72mm f/5.6 astrograph builds on the basic idea of a compact triplet, adding two additional elements to achieve a five-element f/5.6 Petzval configuration with