CS 350

The NortheK Classic Cassegrain 350  f 15 represents a evolution forward from the more specific NortheK Dall Kirkham 250 f 20.

The Classic Cassegrain has an increased correct field compared to the Dall Kirkham and its focal ratio is less extreme so it us suited to more restricted star fields (i.e. clusters, small planetary nebulae…).

This model completes the range of the 350 mm NortheK telescopes for expert amateurs by introducing even higher technical performance and good versatility.

The project of this optical tube incorporates all the best technological solutions available for a Cassegrain scheme, such as the StabilobloK 35 cell, the  composite tube UnitorK 35 and the  modified 2.5″ Feather Touch focuser. Please note  how the focuser included in the price of the FT motor Mkit 30.  This highlights a very important aspect: without an electronic system it is nearly impossible to make the most of the oustanding performances of this telescope.

This is a very standard telescope, intended for users with a good experience in this kind of target and able to get the most also out of the equipment (i.e. seeing, setting up) to thoroughly expoit their investment.

The mechanical apparatus is the exactly the same as the NortheK Dall Kirkham 350 mm f 20.




The NortheK CS 350 is a Cassegrain Classical optical tube (parabolic primary mirror and iperbolic secondary mirror) designed for astronomical observation in high resolution.

It is the best available on the market of mass produced optical tubes and, as such, it incorporates as  many  innovative and highly technological solutions as possible. Its performance guarantees the  optimum value for money.

As far as the optics  were concerned, we opted for Supremax 33 from Schott and chose to keep the thin disc (35 mm) in order to allow the vitreous mass to follow the temperature variation during the  observation session in the best way. Not only: we added an extra three radial fans in addition to the three at the rear (60 mm diameter) to ease the dispersal of the warm air layer on the coated surface. This is a huge advantage in high resolution because is significantly improves the optics performances. The radial and axial fans (optional) can be operated by an electronic control unit to adjust the speed and, because they are mounted on anti-vibration supports, they can turn at low speed even during the observation session.

The platform support for the primary mirror is similar to the one used in the 250 series but with  increased dimensions and capacity. The mechanics have been built with laminates in Halo 25 alloy,  all flattened and with surface accuracy of 0,1 mm/sqmt and a thickness accuracy of 0,05 mm, in order to achieve the aim of not interfering whit the optical discs at all.To guarantee the best support without edge deformation, 6 very strong side pads are provided, incorporating a system for the control of the parallelism of the optical glass discs (normally varying between 0,5 and 0,7 mm). Further details can be found in the technical data sheet of the StabilobloK 35 primary’s cell.

The focusing provided for this model is 2,5″ and, althoug quite long for this diameter, mechanically it performs very well. It’s no good to have an outstanding optical tube if its focusing is affected by every movement. Because this is an optic with a 5,25 mt native focal lenght, it is easy to understand how important it is to maintain the optical and mechanical axis. The key to this problem is the self-centring focusing system.

The UnitorK 35 tube structure  represents the ultimate evolution of the lighter and smaller UnitorK 25 . This improved version has been engineered to  allow a better controll of the forces involved with bigger masses and the carbon structure is also stronger as the aim is to totally avoid any flexions or twisting of the truss tube. The first section of the truss is protected by a very thin aluminium sheet (0,8 mm): a light and elegant but cost-effective solution. This was preferred to a carbon sheet because, from a mechanical point of view, it wouldn’t have given any significant advantage.

The support for the secondary mirror is the well-tested AxyS A1, perfectly  fit for this low obstruction instrument, while the spiders have been increased to 4 in order to improve the AxyS stability on long levers.

If you want to real in detail the characteristics of UnitorK 35, AxyS A1, StabilobloK 35 please go to “Precision Engineering” section of this website and you will be able to appreciate the highly technological content of this telescope.


NortheK Cassegrain Classical 350 : the ultimate instrument for the amateur astronomer!


Optical scheme Cassegrain Classical
Nominal optical opening 355 mm
Actual optical opening 350 mm
Focal ratio f 15
Primary mirror focal length f 3
Actual focus 5250 mm
Back focus 350 mm
Thickness of primary mirror glass 35 mm
Glass of primary and secondary mirrors Supremax 33 from Schott
Substrate Quartzed aluminium SiO2
Optical surface correction diffraction limited
Strehl ratio 0,96
Average reflectivity 94%
Primary diaphragmation 5 mm
Diameter of the secondary mirror 95 mm
Thickness of the secondary mirror 15 mm
Secondary mirror magnification factor 5x
Actual obstruction including the engineering 30%
Diameter of the 100% illuminated field 20 mm
Maximum diameter of the instrument 500 mm
Internal diameter of the tube 450 mm
Maximum lenght of the tube, without accessories 1200 mm
Maximum weigth, without accessories 34 kg
Cell holding the primary NortheK StabilobloK 35
Secondary holder NortheK AxyS A1
Structure of the whole tube NortheK UnitorK 35
Swallow-tailed holder or plate AW361+Losmandy
Outer protection Hard anodization, black colour
Nuts and bolts Stainless steel, Ergal
Standard searcher 8×50 illuminated achromatic
Focus Feather Touch 2,5″
Tool box Included
Maintenance manual Included
Optical cap Included
Primary mirror baffles Upon request
Thermometric sensor Upon request
Optic cleaning set Upon request
Plate to install accessories or other tubes in parallel Included
Feather Touch Mkit 30 motor Included
Data may change without notice


Product code : OTA 350 CS Sale unit : piece
Note: All the stock service products have a standard back focus. It is possible to configure longer or shorther back focus upon request and according to the instrument use. This might require a longer lead time. Before you come to a decision, please ask for details and clarifications.


Product traceability and security codes: every NortheK O.T.A. has its identification number stamped in a specific and fixed position and it contains alla production data and the relevant code of the customer who bought it. This number guarantees the originality of the projects, the traceability of the product and the Made in Italy manufacture. The stamp is laser marked and cripted


Surface deformation primary mirror Classical Cassegrain 350 f 15