CS 250

With a NortheK CS 250 you can enjoy professional performances in high-resolution. This is the Classical Cassegrain, “the” instrument for the uncompromising user, both  in photographic or visual applications.

This optical design is uncommon among amateur astronomers because to achieve the best performances in small diameters requires compes design and construction. NortheK has accepted yet another challenge: to build a high-performance small diameter instrument keeping the costs affordable for an average user.




The NortheK CS 250 represents the optical evolution – from a performance point of view – of the Dall Kirkham NortheK DK 250.

This is an excellent instrument for high  resolution, ideal to  view objects with  a limited angular width. The best  performances are achieved when observing planets but it also gives goods results when viewing star clusters, planetary nebulas and galaxies.

Thanks to its high focal length and the wider corrected field – if compared to a Dall Kirkham scheme – this instrument is ideal for the observation of the Moon and also other planetary surfaces.

The open primary f 3 focal ratio allows the use of a short and compact tube. The design aim has been to achieve the best mechanical stability in order to optimize the optical performance. The optical lay-out is critical thus the cost is similar to the Ritchey Chrétien photographic.

The NortheK CS 250 is the best instrument in its product range, unrivalled from both an optical and mechanical point of view.

Whit this O.T.A., once again, the Maxproject Team has developed an excellent piece of apparatus.

This is the ultimate instrument for the very discerning and competent user.

Optical scheme Classical Cassegrain
Nominal optical aperture 254 mm.
Actual optical aperture 250 mm.
Focal ratio f 15
Effective focal length 3810 mm.
Primary mirror focal lenght f 3 – 750 mm.
Back focus 250 mm.
Thickness of primary glass 25 mm.
Glass of primary and secondary Suprax Schott Germany
Reflective coating type Quartzed aluminum SiO2
Optical surface correction diffraction limited
Strehl ratio 0,96
Average reflection 94%
Primary diaphragmation 4 mm.
Diameter of the secondary 55 mm.
Thickness of the secondary 15 mm.
Secondary mirror focal multiplier factor 5,0 x
Actual obstruction 28%
Diameter of the 100% illuminated field 30 mm.
Maximum diameter of the tool/instrument 360 mm.
Internal diameter of the carbon tube 280 mm.
Maximum length of the tube, without accessories 935 mm.
Maximum weight without accessories 17 kg.
Cell holding the primary NortheK StabilobloK
Secondary holder NortheK AxyS
Structure of the whole tube NortheK UnitorK
Swallow-talled holder and plate Upon request
Outer protection Hard anodization, colour black
Nuts and bolts Stainless steel, Ergal
Standard searcher 8×50 achromatic
Focus Feather Touch FTF 2000 2″
Tool box Included
Maintenance manual Included
Optic cap Included
Primary mirror baffles Upon request
Thermometric probe Upon request
Optics cleaning set Upon request
Carbon joints to add accessories Upon request
Feather Touch MKIT 20 Upon request
 Data may change without notice

The exact optical parameters such as back focus, distance between primary and secondary, dimensions of the glasses, are confirmed exactly in the optical certificate provided with each optic and/or instrument.

Product code: OTA 250 CS – OTA 250 CSN Sale unit: piece


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 product is Made in Italy, its traceability and the origin of the source project. The stamp is laser marked and cripted.