Optics

In all our refractors we use the highest quality optical sets available on the market.

We're currently using the full APO triplet line, from 80 to over 200 mm diameter, designed by Thomas Back and produced at LZOS factory, and other APO triplet objectives developed by our optical designers and produced with the highest quality standards. All LZOS triplet instruments come equipped, as standard, with an interferometric test report. All instruments are tested, verified and collimated before delivery on our autocollimation (double light passage type) optical bench with an artificial laser star at very high magnification.

The LZOS factory, with its huge structure placed Near Moscow, is a recognized reference point for the manufacture of research instrumentation in the astronomy field and, thanks to the absolute high quality, especially in the professional one. Its productive capacities allow to produce monolithic mirrors up to various meters of diameter, and the company is among the very few capable of producing special raw materials for astronomy. Besides the life long experience of the technicians and the very modern equipment used, one of the most important strong points on refracting optics manufacturing, is the internal production of all glasses and optic materials necessary for the production of the finished objectives.

This allows to control the true characteristics of light dispersion of the single glass casting and the attainment, during the manufacturing of the surfaces and their assembly, of the highest expectations in performance.

Every objective produced is mounted, aligned and tested before delivery to Officina Stellare directly in LZOS.

Our task, thanks to our careful mechanics design and final assembly, is to guarantee the attainment of the max imum theoretical possible performances of the objective.

With the help of the page "Essay on Optics" written by Thomas Back on his web site, we want to help the customer to have a sharp idea of some definitions widely used on the apochromat refractormarket.

In this text which we report below there are also some important infos on the material used for the LZOS objectives and on their performances.

"Apochromatism": an old definition

With the proliferation of apochromatic refractors that are available to the amateur astronomer, it is time to define the parameters of a true apochromaticobjective lens.

The modern definition of "apochromat" is the following: an objective in which the wave aberrations do not exceed 1/4 wave optical path difference (OPD) in the spectral range from C (6563A - red) to F (4861A - blue), while the g wavelength (4358A - violet) is 1/2 wave OPD or better, has three widely spaced zero color crossings and is corrected for coma.

"Apochromatism": a brief history

Abbe, working for carl Zeiss during the last years of 1800, discovered that by using optically clear, polished natural fluorite, in a microscope objective, the ‘apochromatism' could be achieved. These first true apochromatic microscope objectives were so superior to the competition, that Zeiss gained nearly the entire high end market. So secret was the use of fluorite, that Abbe marked an "X" on the data sheet for the fluorite element, so as to keep it secret from the other optical companies.

Abbe's definition of apochromatism was the following.

Apochromat: an objective corrected parfocally for three widely spaced wavelengths and corrected for spherical aberration and coma for two widely separated wavelengths.

This definition is not as simple as it sounds.

Abbe's definition, to put it in clearer terms (I hope) is that a true apochromat is an objective that has three color crossings that are spaced far apart in the visual spectrum (~4000A, deep violet to ~7000A, deep red).

But what about the levels of spherical aberration at each of these wavelengths?Abbe, in his definition of apochromat, states that spherical aberration must be corrected for two widely spaced wavelengths.

Materials

All our refractor OTAs are made of aluminium (6061 anticorodal - 7075 ergal) for the rear and front assembly (fully CNC machined) and true carbon-graphite fiber for the tube (high module true carbon-graphite fiber, obtained in high vacuum chamber).

Each OTA is machined to the highest tolerances and is computer optimized to be lightweight with the best structural rigidity. The internal baffles (we use up to 7 internal baffles for the tube, from the lens to very close to the focuser and others directly inside the focuser) are laser cut from stainless steel and glued to the tube with a professional glue.

The true carbon-graphite fiber allows to obtain a very stable focus position at very large temperature variations and is very lightweight, really useful for great diameter refractors.

Design

In our OTAs we use the original lens cell provided by the optics manufacturer, the installation is carried out very carefully and particular attention is used to avoid introducing any mechanical stress on the lenses.

Our dew and light shield is fully retractable to make the tube size very compact for transport.

We put a lot of attention in all our design to prevent any internal reflection (using very opaque paint, even on all the laser cut internal baffles, and black velvet on all other parts) and scattered light. This allows to obtain the max imum performancesof the optics.