Classic Cassegrain 250 mm

Availability: Product sold-out Type: reflector

* This product has been discontinued; no new orders accepted*

Our Cassegrain reflectors are designed for high-quality visual astronomy, with strong performance in planetary and lunar observation, as well as deep-sky targets such as globular clusters and nebulae. They are also well-suited for planetary imaging.
Each unit combines effective light-gathering capability with carefully crafted mirrors housed in a precision-engineered chassis, allowing for straightforward and stable collimation.
Despite common misconceptions, properly designed and executed Cassegrain optics can produce coma-free, pinpoint star images across the field of view, whether using 1.25″ and 2″ eyepieces.
We offer a comprehensive selection of optical substrates to suit a range of performance needs and budgets:

Supremax33 Borosilicate Glass (Schott) – Fine-annealed and cost-effective, ideal for entry-level applications.
Fused Silica / Quartz (Ohara's SK-1300) – Ultra Low Expansion (ULE) material with excellent thermal stability.
Clearceram-HS (Ohara) – glass ceramic material with ultimate level of thermal stability.

For apertures of 350 mm and above, we strongly recommend Fused Silica / Quartz or Clearceram-HS, both of which deliver superior thermal behaviour and exceptional optical surface quality.

Key features:
* 2" rack and pinion type focuser from Starlight Instruments, 50mm travel.
* Precision adjustment of primary & secondary mirror.
* Portable, medium size reflector telescope.
* Truss type chassis design for stability and quick cool down times.
* Carbon fibre and aluminium alloy, high quality chassis/frame.

Specifications & technical data:
Clear aperture – 250 mm; Focal ratio – F/15; Focal length – 3750 mm; Central Obstruction – 34%, linear
Clear aperture – 250 mm; Focal ratio – F/20; Focal length – 5000 mm; Central Obstruction – 28%, linear
Primary substrate – Supremax33, Fused Silica/Quartz, Clearceram HS.
Secondary substrate – Supremax33, Fused Silica/Quartz, Clearceram-HS.

Dimensions:
F/15 version – 900 x 345 x 380 mm (L x W x H)
F/20 version – 930 x 345 x 380 mm (L x W x H)
Weight = ~13 kg*
Usable back-focus = ~190 mm*
*Variations may occur with individually produced components.

Pricing:
*Product phased out, unavailable for ordering*

Included items:
– 2" Starlight Instruments focuser, rack and pinion, 50mm travel
– shroud pack (secondary casing shroud, secondary cage shroud, truss shroud)
– side plates (pair)
– riser + finder shoe (Starlight FSB-CH)
– primary mirror cooling fans
– primary mirror heater
– primary mirror hard cover
– 350 mm D-type dovetail
– handle.

Coatings:
standard coating reflectance: 92% (SiO overcoat), included in the price.

Optional accessories to consider when ordering:
Additional dovetail, Losmandy Type, lightweight, to replace the handle.
Controller for heaters and fans (several variants available for integration).
Electronic focusing package for FTF-2020RP.

Visual accessories:
A prism or mirror diagonal will be needed, together with good quality eyepieces, to be able to extract the most of your new telescope.

Number of units manufactured/ordered: 17
Number of F/15 units manufactured/ordered: 5
Number of F/18 units manufactured/ordered: 2
Number of F/20 units manufactured/ordered: 10
Units available for ordering: none, product unavailable for ordering, starting with October 2020.

* Prices subject to change without notice.
* Net prices are exclusive of any applicable duties and taxes.
These are the responsibility of the Buyer and may be charged by your local customs authority upon delivery.

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