The telescopic mast consists of 8 tubes.
Other advantages are those common to all telescopic sights.
The shaft is lined with a cylinder of wrought iron, within which a tubular chamber, provided with doors above and below, known as an P g air-lock, is fitted by a telescopic joint, which is tightly sinkin packed so as to close the top of the shaft air-tight.
This was done in 1612 by Christoph Scheiner, who fully described his method of solar observation in the Rosa Ursina (1630), demonstrating very clearly and practically the advantages and disadvantages of using the camera, without a lens, with a single convex lens, and with a telescopic combination of convex object-glass and concave enlarging lens, the last arrangement being mounted with an adjustable screen or tablet on an equatorial stand.
The smallest and most numerous class are the telescopic meteors invisible to the naked eye.