ABOUT STF TELESCOPES
STF Telescopes specializes in manufacturing of Maksutov-Cassegrain telescopes. There are currently two models manufactured: a 7-inch telescope Mirage -7 and an 8-inch telescope Mirage-8, both with different modifications. The production of these scopes is controlled at all stages with the help of an interferometer that results in superior quality of the wave front ( /6, /8, /10 and better) and a high resolution. The telescopes have precise mechanics preventing image shift when reversing the focusing. Collimation is not affected during transportation. Anti-reflective paint and thread on the inside surface of the telescope allow to make high-contrast pictures of the night sky. All these qualities along with compactness, small weight and reasonable price earned these telescope high regard among astronomy enthusiasts.
Mirage telescopes are of the Maksutov-Cassegrain type. The optical schematic diagram is shown in Picture 1. It consists of two mirrors (the main one - 1, and the secondary one - 2) and a meniscus lens 3). The ratio of the secondary-mirror diameter (d) to the input-aperture diameter determines the magnitude of screening. This magnitude in percentage points is (d/D) ? 100%. Screening is in fact the main drawback of this system. It decreases the performance index of light and reduces image brightness of linear objects. However, if the screening does not exceed 33%, its influence is minor. Besides the quality of dot objects (stars) images turn out to be not worse than in ideal optical systems that have no screening, and sometimes the quality is even better. There is some slight decrease in contrast only when observing linear objects (planets). The advantages of this system are:
1) Compactness. With the focal length and light collecting aperture being the same this scope is 3,5-4 times smaller than the scopes with the same focual length but without central screening.
2) It is much easier to manufacture making it cheaper.
Since these telescopes are light in weight, they require light and cheap mountings(?) (of EQ5 and EQ6 types). Our version of such scopes has the following advantages:
1. Focusing is done by movement(?) of the main mirror preventing transverse(?) shifts of the image when reversing(?). Moreover, this design is not affected by the weight of accessories, which cannot be said about telescopes with focusers.
2. The movement of the main mirror allows changing the back focus from 90mm to 290mm, which means that the focal surface can be shifted within 200mm. This makes it possible to use practically any accessories.
3. The diameter of the diffraction spot is 8-10 mkm. This allows to get celestial images of great quality.
4. The telescope is made of a whole aluminium tube making it (?) firm and rigid.
5. Each scope is tested on the interferometer and has a certificate with the inerferogram, in which the wave front error is given in wave length. fractions
The telescope package is specified in the catalogue. To obtain the observation system, the scope must be provided with accessories and mounts.
A mount is chosen in accordance with the weight of the scope. This is the basic requirement. Some mounts have a dovetail mounting plate. That's why to set up our telescopes it is necessary to have dovetail adapter..
As a rule, the following accessories are used for observation:
1) Diagonal mirrors. They enable to carry out observation in the zenith area of the starry sky.
2) Oculars. They enable to carry out visual observation and to change the magnification.
3) Barlow lens. It is used together with the oculars for increasing the focus of the scope and it enables larger magnification.
4) Adapters. They enable attachment of different accessories to the telescope.
5) Reducers. They enable increase of the the lightforce(?) of the scope. They are used only for taking pictures of stars and Star Clusters.
6) Camera bracket.. It enables to attach a camera on the telescope.
7) A dovetail adapter - it is required for STF telescopes if mounts with a dovetail mounting plate are used.