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by Josef Vnucko, Czech Republic, 2013
For several months I have been using this type of telescope, which I invented, built and successfully used for planetary and other objects for which large magnifications are appropriate, eg Moon, planets, double stars and others. The basis of my design is the Newtonian telescope. Excellent primary and secondary mirrors are needed for good results. The telescope has a shifted and smaller secondary mirror compared with a conventional Newtonian, thus reducing the obstructed area up to 15% and makes better use of central rays. The eyepiece is replaced by an eyepiece adapter - basically a microscope with appropriate objective parameters and therefore with good light aperture.
Even the first looks reveal exceptional quality when using great magnifications without any of the distracting aberrations which appear using a classical construction. An optical diagram and a trial recording is attached to this report. It is important to mention that a high quality image is only available on the optical axis, and around it.
The telescope must be perfectly collimated.
When construction calls for the use of a high quality secondary mirror, it is necessary to verify the quality of the mirror that you use. Mirrors are offered with varying quality, often you can get poor quality even from reputable companies. I have had good results with mirrors from czech company ATC-Prerov, which offered good quality mirrors at a reasonable price. It is also necessary to matt black inside between the lens and eyepiece perfectly, preferably using glued shades, otherwise the image loses contrast.
Excellent results are achieved if the secondary mirror obstruction is 15% or less relative to the primary mirror. For example, if you use the mirror aperture of 1:6 secondary mirror shading can reach up to 10%.
Telescope resolution on the optical axis surpasses all existing types of telescopes - Schmidt-Cassegrains, Maksutovs, Super-apochromat lenses and others. This comparison was practically tested many times. I attach a test recording of terrestrial, not too distant object. This video was created with regard to the elimination of seeing and is done through a modified telescope Sky-Watcher 150/750 mm. The focus is stretched to 1350 cm, which presents the magnification of 9D !! Small axis of secondary mirror is 18 mm (12%).
As reading lenses are used standard microscopic achromatic objectives 4x, 6x, 10x, 15x. For visual observing I use orthoscopic eyepiece f = 10 mm (rapid calculation of final magnification). I recommend use 16-17 cm distance between F1 and F2 for which these microscopic lenses are calculated. The sample recording is created by usual type of FSAN security camera, model 9811Q97 with AV output, which I use for on-line astronomical observations.
In practical tests of this type of telescope, the image was good even when enlarged 9D, while the practical compared to the high quality apochromatic telescope LZOS 115/805 mm the image at a magnification 7D of APO lens was slightly blurred and not sharp, so in this type of telescope was virtually blur-free picture, sharper and clearer.
I currently have reworked and used telescopes with mirrors 1:4 (300 mm), 1:5 (200mm.1: 4 (150 mm), 1:5 (150mm). With the last one I made a movie that I sent with this article.
Many thanks to Jan Zahajsky, Jiri Lev for participation to technical realization of this project.
Optical design, construstion, text, photos and video: Josef Vnucko, Czech Republic, 2013
Question and ideas please send to my mail: firstname.lastname@example.org or send PM to josef-cz on CN-Forum.
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