74-inch reflector, Helwan (Kottamia), Egypt, 1963.

In the 1940s it was decided that a larger telescope was necessary and in 1948 the Egyptian Government placed an order with the British firm Grubb-Parsons for a new 74-inch telescope equipped with both Cassegrain and Coudé spectrographs. The telescope and spectrographs were expected in 1955. However, owing to numerous difficulties, delivery was delayed until 1960. First light was achieved in May 1964. Ref: www.saao.ac.za/~wgssa/as2/hassan.html

In order to maintain Egypt's position in the international astronomical community it was considered desirable to make use of recent developments in mirror-making technology to modernize the approximately 35-year old 1.88-metre Kottamia telescope. Supported by one of the major resolutions of the Fourth United Nations/European Space Agency Workshop on Basic Space Science, which was hosted by the Government of Egypt in 1994, the question of modernizing the telescope was raised with the Egyptian Government. After extensive discussions between NRIAG and the Egyptian Government this project was approved and funded. The modernization of this telescope is especially important in view of the fact that it is the largest telescope in North and Central Africa, as well as in the Middle East. The importance of modernizing this facility, which would supply major experimental capabilities for basic space science in the region, is enormous.

The contract to refurbish the Kottamia telescope was awarded to the German company Zeiss in 1995. This involves equipping the telescope with new primary (M1) and secondary (M2) mirrors made of Zerodur glass ceramics. The new optics have already successfully passed acceptance tests at the Schott Glassworks in Mainz. Ref: www.saao.ac.za/~wgssa/as2/hassan.html

Edit (29/0418). It appears that the original mirror (made from the borosilicate glass Hysil) accumulated surface damage as a result of acid cleaning before re-coating. This eventually resulted in the mirror not being able to hold a good coating rendering it unusable. Ref : https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1539299600012521

See also : http://womenslens.blogspot.com/2011/02/helwan-observatory.html

The 74 inch Telescope at Newcastle.

A nice summary from https://www.researchgate.net/figure/Kottamia-74-Telescope_fig1_267037662....

In 1905, Mr. Reynolds, an amateur astronomer at that time and later treasurer of the Royal Astronomical Society in London presented Helwan Observatory with a 30" reflecting telescope. Due to the clear sky of Helwan and the ability of the astronomers in charge of this telescope, a great deal of valuable observations was collected. As of the curiosity of astronomers to achieve more, a large telescope was necessary and a 74" telescope equipped with both Cassegrain and Coude spectrographs had been recommended to the Egyptian authorities. The Egyptian government signed a contract for this purpose with Messers. Grubb Parsons of Newcastle. U.K. in the same year (1948) that the giant 200" telescope of Mount Palomar California was erected. The delivery of the telescope and spectrographs was expected in 1955, but various difficulties arose which resulted in a considerable delay of delivery until 1963 (Samaha, 1964). Kottamia mountain (about 80 Kms. NE of Helwan, 12 km. north of mid-point of El Maady Cairo-Ein Sukhna road, 476 meters above see- level) had been chosen for the location of Kottamia Astronomical observatory (KAO). The latitude of the observatory is 29° 55 ́ 35.24" N; the longitude is 31° 49 ́ 45.85" E. The seeing conditions prevailing at the site is around 2 arc sec. in average (Hassan, 1998). KAO belongs to the National Research Institute of Astronomy and Geophysics; NRIAG (previously, Helwan Observatory). The reflector is of conventional design, having a parabolic mirror with secondaries to give Newtonian, Cassegrain and Coudé foci. The mounting is of English type with north and south piers that support a polar axis with the tube offset on a short declination axis (Issa, 1986). A photo in Figure 1 shows the Kottamia telescope with its Cassegrain and Newtonian foci. The main mirror has an aperture of 74 inches and a paraboloidal surface of 360" focal length (F/4.9). The Cassegrain secondary has an aperture of 19" and a hyperbolic section giving a focal ratio of F/18, with plate scale of 6.1 arcsec/mm. A second hyperbolic mirror similar to the Cassegrain has a focal ratio of F/28.9 and in combination with two flats of 13.5 inches and 9.5 inches apertures give the Coude focus plate scale of 3.8 arcsec/mm. The Newtonian focus has a focal ratio of F/4.9, thus giving a scale of 22.53 arcsec/mm. A review of the values of focal lengths, F/ratios and plate scales at various foci of the telescope is given in Table 1. The dome was constructed by the united Austrian Iron and Steel Works (VOEST) of Linz/Austria. It is 18 m in diameter with an outer shell of galvanized steel plate painted externally with aluminum. The dome is very good insulated from heat and dust which lead to diurnal range of temperature variation to be as minimum as 3 °C. A photo showing the dome is given in Figure 2. The dome can be rotated at a speed of one revolution in six minutes by means of 6 three phase motors driving pinions into a circular rack. The dome runs on 26 traveling wheels and is kept central by means of 15 horizontal guide rollers placed around the circumference to allow for thermal expansion and distributions of wind loading. The dome has two shutters, an upper and a lower capable of moving at 1.5 m/min. Hand operation is possible in case of emergency. The upper shutter is of the “up and over” type whereas the lower shutter is in two parts each opening to the side. A canvas wind screen provide the protective action of the lower shutter. The opening of the dome is 5 meters wide and extends 2.5 meters beyond the Zenith. An observing carriage traveling at 4 m/min is fitted with control buttons for dome rotation, shutter operations and its own motion. It runs on rails attached to the main arches of the dome. Similar control pushbuttons are also provided at various positions around the periphery of the dome. At present there are no electrical control connections between the telescope and the dome. Some few years ago, the dome control has been upgraded by one of us (F. Elnagahy) to an RF handset control. As the telescope tracks the object across the sky, it is necessary to rotate the dome from time to time to allow the light of the object to enter to the telescope. This is being done recently by the RF handset control instead of pushbuttons around the periphery of the dome, which previously necessitated a person to go up the stairs to do such movement action. In order to share astronomical communities their enormous contributions in astronomical research, it was necessary to modernize an approximately 32-years old 74" telescope. The matter was raised to governmental authorities and after some long subjective discussions, it was approved to support Kottamia telescope with the necessary money for upgrading. In 1995, an appropriate agreement was signed with Zeiss company (FRG) to design a new optical system for the telescope. This involved a new primary mirror, secondary Cassegrain mirror both are made of “Zerodur” glass ceramics, and a new supporting system for the primary mirror (Hassan, 2004). Due to some complications and problems in the design of the supporting system, the system was not approved until 2003 when it was being in effect and working properly.