20-inch (500mm, 25 mm FLOAT GLASS) F/4.5

The 'Primary Mirror' is the principal light-gathering surface of a reflecting telescope. The Primary Mirror is also known as the Objective and is the heart of a good telescope. The performance of a telescope is mainly dependant on the quality of its Primary Mirror.

The main considerations for purchasing a Primary Mirror are as follows:

1. Diameter of the Primary,
2. Thickness of the glass substrate,
3. Glass substrate material,
4. Quality of reflecting surface, accurately parabolised, smoothness of micro surface,
5. Reflectivity and quality of aluminisation and protective coating.

At Aperture Telescopes, we offer Parabolic Primary Mirrors in diameters of:

1. 200 mm (8-inch),
2. 250 mm (10-inch),
3. 300 mm (12-inch),
4. 400 mm (16-inch),
5. 500 mm (20-inch).

All proudly Made in India, right here at our optics shop at Manesar, Gurgaon. We have a complete in-house production facility. All our primary mirrors are precision made and finished with hand figuring to a perfect parabola. The mirrors are frequently tested for accuracy of overall figure as well as for the smoothness of the surface.

All our Primary Mirrors are guaranteed to a Strehl Ratio of 0.90 or better. The best opticians now use the Strehl ratio for specifying the quality of primary mirrors. A Strehl ratio of 0.8 is good, 0.9 is excellent, 0.95 or better is outstanding. Apart from the Strehl ratio, we endeavour to produce an excellent smooth surface with no micro ripple or roughness. A smooth surface provides a much better contrast at the eyepiece, and is especially beneficial for revealing fine detail on planetary surfaces.

We offer Primary Mirrors made from Float Glass, thickness 25 mm. In the near future we will be in a position to offer fused glass primary mirrors of 38 mm thickness. Float glass is a softer than other glass materials and consequently it can be polished to a great degree of accuracy and smoothness. Thin glass blanks of float glass achieve thermal stability quickly. Please go through this essay on Float Glass Mirrors.

We coat our mirrors with aluminium in a vacuum coating chamber and finish with protected coating of SiO2 which guarantees the highest longevity and efficiency of 93% reflectivity.

All our mirrors have serial numbers as well as a complete report of its testing. Our mirrors are centre marked for ease of collimation.