One of such instruments was 13" reflector, fully engineered and completed in the end of October 1932, and intended for mounting at the Institute's Mountain Astronomical Observatory in Abastuman.
13" reflector was mounted on similar scheme like the 60" Mount Wilson telescope. It's mount was designed to install instrument at the latitude 42°30'. It works in the following 4 optical schemes, each of them has special splinted demountable part.
Main mirror of the telescope had diameter 33 sm and focal length 1655mm light-gathering power 1:5. Preliminary grinding was done with the coarse abrasive till curvature was reached. Final grinding was done with the smaller abrasive fractions and levigationed in the water (1,5,10 and 30 minutes) fractions. Polishing had been done with special polishing pad made of wood pitch and using rouge as the polishing material. During polishing was started to inspect optical quality of the main mirror by using Fuco method of measuring longitudinal aberrations. For this object star simulator device with fine adjustment screw was manufactured in Institute's mechanical workroom. Main mirror was examined from the center of curvature and by the shadows seen on the mirror surface and measuring it's longitudinal aberrations it could be estimated about quality. After main mirror was examined in the autocillimation scheme with a big flat mirror with light source in the focus of paraboloid. In the final tests founded aberrations not exceeds 0,1 mm. Thus quality of the main mirror was quite good. Theoretical quality is 0.05 of qreenwave, i.e 1:40000 mm. The last phase was silver coating and mounting mirror in the tube.
Ocular unit consists of rack mechanism and mounting plate on which can be mounted eyepiece or photographic plate (6x6 sm) covered 30 sq. min of the sky.
Worm gear. Right accession movement of the reflector does by means of series worm gears. By this it is difficulty to make worm teeth pitch constant, i.e. to do periodical error minimal. Fabrication of the parts of the worm gear was done by following procedures: on the screw-cutting lathe (Boley&Leylen) worm had been toothed with the tooth step 1.5 mm, diameter 20 mm and length 80mm. Checking of step persistence done by All-Union Intitut of Metrology and Standardization, at last Chamber of Measurements and Weighting) on the Carl Zeiss comparator with accuracy 0.1 mkm. Checking results that worm has step persistence 0.2 mkm. As calculations shown to reduce whole reduction ratio needs to insert additional worm gear with the triple spiral worm of 9 mm step and diameter 22 mm. Checking of step persistence also done by checking results that worm has step persistence +3 mkm. It's twice over needed for this worm gear.
Gear had been toothed in Russia for the first time. It had diameter 480mm and 960 toothes, i.e. during each 90 sec. gear rotated on 1 tooth and it corresponds to one worm revolution with 1.5 mm step. With the help of additional worm gears main gear does one revolution per sideral day. Gear had been toothed on the milling machine (Schuchsrdt&Schutte). Ball bearing mounted gear was preliminary grooved and after toothed gear-milled cutter with modulus 0.5. Final toothing done with precision hobbing cutter (made by Sestroretsky toolmaker factory) basing breaking-in technique.
Usually process of manufacturing of worm gear is as follows: the screw is preparing with the precisely same step, diameter and length, what are necessary for worm hob. After that on miller machine longitudinal grooves are slotting for formation cutting edges and the worm hobl is ready. Now it is only necessary to do thermal processing in the special bake oven. These operations are most dangerous, since the hob exposed by its internal tension able to cause of a crack and buckling. To avoid it and achieve of the maximal accuracy Sestroretsky toolmaker factory made a worm hob not on the screw-cutting lathe but on grinding machine, i.e. spiral groove and longtitudal groove were milled on the hardened surface with the special flute-grinding wheel. Only such way of manufacturing of a worm hob has enabled to achieve step quality nearly 1 micron. After hob the wheel was attached on the top part of a polar axis and matched with worm gear located on an arm. The hour wheel together with worm gear was very precisely adjusted and by means of especially mounted from the motor belt transmission was started and regrinded with levegated from ribber brick abrasive dust. The operation of regrinding proceeded about two weeks, i.e. before reception of a regular and smooth movement.
Limbs. Rather serious and crucial work was a division of the right ascension and declination limbs. The difficulties were increased because the workshop of Institute had no special machine to do these work and consequently all work should be executed on universal — milling machine with a special tool. Limb was made for RA axis had a diameter of 350 mm and accuracy within 1 minute, i.e. was divided on 1440 partitions. Limb for declination axis had the diameter of 300 mm and also was divided to achieve accuracy within 15' arc min, i.e. was divided on 1440 partitions.
Clock drive and guide. The clock drive mechanism is an unique and only one serious part received for reflector from Carl Zeiss in 1930. The guide was acquired from private hands and is a 2.5" small viewfinder given the quite good images. Micrometer was also adapted to the guide.
Tests. The first attempts to perform star tests of the reflector were made on 3 September, 1933. But then still nothing could be told about quality of the instrument since the mirror was not alignment yet. It was only possible to ascertain of the reflector quality on September 14, during a lunar eclipse. This evening it was possible practically to define resolution appeared equal about 0.7". The theoretically required power for the instrument is equal 0.5". The definition of the resolution power was made by observing of double stars. In particular were observed double е1 and е2 Lira, which were very precisely resolved into pairs. Star clusters located and globular ones in Hercules, Andromeda Galaxy, various objects of a lunar surface etc. very well were visible also.
Through photo-electric photometer the regular study of change of brightnesses variable stars such as Algol and also definition of their colour was supposed; study of change of brightnesses of the companions of planets and asteroids, on advantage of objects with weak amplitude in change of brightnesses. With the help of the chinkless spectrographic quartz camera the study UV- part of spectrum and study of a physical structure of comets was supposed. Reflector was also been intended for use at various researches of a Solar surface. Moreover the task of an establishment of homogeneous system of photographic and visual magnitudes, study of a nature of a dark nebulaes were done by study of their colour, and also there distribution in space. Tasks of spectrographic research of separate stars with the quartz spectrographic camera & photo-electric photometer, study of brightness of spectral-double systems also were put.
Article is prepared by Oleg Sankin on basis of the materials of Russian Astronomical Calendar (XXXVI, 1933)