High-quality quintuplet air-spaced ED glass Petzval Astrograph The 70mm aperture f/4.8 quintuplet air-spaced lens design offers a focal length of 336mm. The objective lens includes two elements of ED glass. The central star point has an RMS radius of less than 1.84 μm, and the star point at the corner is less than 2.4 μm. It also has excellent full-field illumination and MTF data. The integrated self-flattening Petzval design supports a 44mm full-frame image circle so there is no need for additional flatteners and no need to calculate back focus.