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Apochromatic refractors (APO´s) for astrophotography

The refractor follows the classic telescope design - a long, thinner tube pointing into the sky and an eyepiece at the bottom. The incident light is collected by the objective, consisting of one or more lenses. Apochromats are refractors (APO´s) whose lens design is designed to combine at least three colors (red, green, blue) into one focal point. This corrects the chromatic aberration (a shift in colors, fig. A) typical of refracting telescopes.

fig. A: Example of chromatic aberration

fig. B. Stars without shift in colors

Coronado SolarMax III 70 mm H-Alpha Solar Telescope with BF15 Blocking Filter

Technical details:

Diameter of the objective: 70mm
Diameter of the etalon filter: 60mm (Band width: <0.7 Ångström)
Clear aperture blocking filter: 15mm
Focal length 400mm
Aperture ratio (f / 5,7)

Baader Fluorit Flatfield Converter 3x bis 8x Barlow Linse

The FFC allows the focal length to be significantly extended without affecting the sharpness of the image.

A Barlow lens is an optical component that is inserted between the eyepiece and the focuser. Inside there is a negative lens that extends the focal length of the telescope.