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This Page Updated
30th October 2021


  • The Takahashi Mewlon-250CRS Telescope is a flat field corrected Dall-Kirkham that provides amazing results when used for imaging or visual pursuits.
  • This Mewlon-250 includes an installed 3 element ED corrector.
  • The Takahashi Mewlon-250CRS incorporates Active-Focus, an ASCOM compliant computer focusing feature.
  • The system also includes a three-fan computer controlled cooling system. An included hand controller is used to control focus and cooling.
  • A 7x50 Finder Scope is built-in with the OTA
When Takahashi developed the correctors for their Mewlon line of telescopes it meant that any Mewlon-250 or 300 ever made could be converted into a flat field corrected telescope. This 3-element ED corrector allowed the Mewlon to be used as an imaging instrument or used as a corrected visual instrument capable of producing flat-field corrected views of the Moon, planets and deep space objects. The 250/300 Mewlons use an electric focus controller that moves the secondary mirror. Takahashi developed the secondary focusing system in 1990 and wanted to improve them with computer control. An ASCOM driver is available for download free from Takahashi Japan website.

The CRS Mewlons are the product of this development. They both employ an ASCOM compliant driven secondary focusing motor that allows the Active Focus system to be controlled by an ASCOM compliant focusing system.

Additionally, to make imaging easier a 3-fan cooling system is included. This system uses three sensors: one on the mirror, a second in the tube and a third outside to monitor and control the low vibration fans to bring the primary to ambient temperature. This can be done manually or controlled by an ASCOM compliant focusing program.

The cooling system is controlled manually or automatically with the hand control. When the sensors read a difference in the temperature of the primary and ambient temperature the fans turn on and cool until the primary is brought to ambient.

The provided hand control is used for manual focusing and cooling and as a connector for the computer controlled focusing program

The USB port is used for the connection to the computer for auto focusing.

The auto focusing system is called Active Focus. Active Focus includes a backlash revision function. The M-250CRS uses a four vane spider to support the pulse motor focusing system. It can be controlled with FocusMax, Maxim DL or similar software.

The M-250CRS is an outstanding medium sized flat field imaging and visual instrument. It weighs 22lbs so it is portable and does not require a large mount to operate, so it can be easily transported to remote sites.

A dedicated f/7.3 reducer and 1.5x extender are available optionally for added flexibility.
Mewlon-250 CRS M27 taken with Mewlon-250
M51 taken with Mewlon-250  Mars taken with Mewlon-250 Jupiter taken with Mewlon-250
Mewlon-250CRS Components
Mewlon-250CRS Cooling System Mewlon-250CRS Rear Mewlon-250CRS Focus Hand Controller
Mewlon250CRS Mewlon250CRS Mewlon250CRS Mewlon250CRS
Mewlon-250CRS Technical Specifications
Optical design Corrected Dall-Kirkham (Cassegrain) 
Effective aperture  250mm 
Focal Focal Length 2500mm
Effective Focal Ratio f/10
Secondary Mirror 72mm
Resolving Power 0.46 arc/sec
Limiting magnitude 13.8
Light grasp 1275x
Image circle 40mm
Back focus 180.8mm
Metal Back 115.5mm
Diameter of Main Tube 280mm
Total Length of Main Tube 945mm (37.2")
Total Weight of Main Tube 12kg (26.4lb) w/7x50 Finder
with Reducer-CR 0.73X
Effective Focal Length 1825mm
Effective Focal Ratio f/7.3
Image circle 35mm
Metal Back 72.8mm
with Extender-CR 1.5X
Effective Focal Length 3780mm
Effective Focal Ratio f/15.1
Image circle 44mm
Metal Back 117.5mm
MEWLON-250CRS Photo/Visual System Chart PDF - CLICK HERE





The above images and information and gathered from various online sources

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