The Mewlon Series of Dall-Kirkham Telescopes by world-renowned TakahashiJapan combines refractor-like performance in a larger folded optic reflector design.
The Mewlon-300CRS is the largest of the Corrected Dall-Kirkhams made by Takahashi. The internal 3-element ED corrector transforms the M-300 into a corrected flat-field instrument. An integral pulse motor controls secondary focusing, and is considered among the most advanced computer controllable focusing systems available today. The focus system called Active Focus can be computer controlled by ASCOM compliant programs such as Focusmax and Maxim DL.
A free of charge ASCOM driver is available for free download from www.takahashijapan.com website. It enables the focus control and full control of the cooling system. Backlash control is also included to insure precise focus for imaging or visual applications. The M-300CRS includes the pulse motor controlled secondary focuser as standard equipment This new focuser is the successor to the step motor secondary focusing system introduced by Takahashi in 1990 and is still used on the Mewlon-250 and 300. Additionally, a hand control that can focus manually or with USB connector to a PC is included.
Further, to aid cooling a low vibration three fan system is standard equipment. This system uses three sensors: one on the mirror, a second inside the tube and a third outside the tube to properly measure ambient temperature which enables the cooling system to be operated either remotely with the hand control or by a PC through a convenient USB B connection that is provided on the hand controller for easy computer connection. For manual operation the fan button is pressed to turn on the cooling system. Focusing is powered by a 12v AC power supply for computer focusing or four AA batteries for hand unit focusing
The M-300CRS is a flat field corrected telescope that produces flat field, high contrast images and pinpoint star views across the entire field due to its three element ED permanent corrector. This is a perfect match for the new Takahashi UW flat field 90° eyepieces.
- Optical system: Corrected Dall-Kirkham
- Effective aperture: 300mm
- Focal length: 2960mm
- Effective focal ratio: f/9.9
- Image circle: 40mm
- Tube diameter: 324mm
- Tube length: 1045mm
- Weight: 27kg-59.4lbs
The Mewlon series of Dall-Kirkham Cassegrain telescopes from Takahashi offer the experienced observer a level of performance and portability not found in other Cassegrain telescopes mass produced for amateurs. Classical Cassegrain telescopes offer excellent performance but they are extremely expensive to produce at large apertures. By concentrating on the Dall-Kirkham Cassegrains, the Mewlon offers a professional level of performance within reach of most amateurs.
The Mewlons use an ellipsoidal figure on the primary mirror and a spherical figure on the secondary. By focusing on very tight tolerances for these surfaces, Takahashi is able to deliver a compact telescope with reasonable aperture and high resolution. Where fast F/ratios are not required, the F/12 Mewlons provide excellent contrast by utilizing a smaller secondary mirror than comparable Cassegrain designs. Secondary obstruction as a percentage of diameter is 29-31% on the Mewlons. Classical Cassegrain telescopes usually have secondary obstruction of 32% or greater. Commercial Schmidt-Cassegrains have secondary obstructions of approximately 38% for F/10 systems. Ritchey-Chretien Cassegrains have even more secondary obstruction making them less suitable for visual, high contrast applications.
Takahashi uses extensive knife-edge baffling to minimize stray reflections as well as a specially designed tube that also acts as a light baffle. The result is an instrument that rivals an excellent long-focus Newtonian or refractor for contrast and sharpness. Some opticians have criticized the Dall-Kirkham design as having unacceptable coma. With most eyepieces (including Panoptics & Naglers) the coma is negligible and well outside the field of view. Stars are much smaller and sharper than in commercial Schmidt-Cassegrains. Coma may be a problem for wide-field astro-imaging, but these instruments were not designed for such tasks. With Takahashi's field flattener/reducer, these instruments offer superb off-axis images at F/9.
The 250mm and 300mm models have electronic focusing accomplished by moving the secondary mirror. This eliminates the image-shift problem inherent to commercial Schmidt-Cassegrains with moving primary mirrors. Because of the loose tolerances required in moving large and heavy mirrors on a baffle tube, most SCT's will not maintain perfect collimation. Image quality is then compromised in such optical systems. The large Mewlons also have removable covers for their primary mirror cells, this aides in rapid mirror cooling so that the observer can take advantage of favorable seeing conditions more quickly. These features make the large Mewlons ideal for high-resolution CCD imagery.
With the Mewlon series, one doesn't have to sacrifice optical performance for high portability. The 8.3" Mewlon 210 weighs just 18lbs (8.2kg) with a 7x50 finder attached. The Mewlon 250 weighs only 28lbs (12.7kg) and is remarkably compact for a 10" Cassegrain. Both of these instruments are highly portable and offer deep sky views that are exceptional. On the planets, many observers have reported seeing details they thought impossible with telescopes of this aperture. With the exception of a few diffraction spikes around bright stars, on might believe they were observing with a large apochromatic refractor. The advantage, though, is a greater amount of light grasp and resolution than a comparably priced refractor. Indeed, the Mewlons offer an exceptional value in their aperture class.
So if you desire a professional grade instrument in a compact, lightweight package or are tired of compromising light grasp for crisp detail and contrast, check out the Mewlon Cassegrains by Takahashi. You will be pleasantly surprised by their performance. For further analysis of the Takahashi Mewlon Series of Dall-Kirkham Cassegrains, please read Jean Dragesco's review in his book High Resolution Astrophotography, Cambridge University Press, 1995.
|Name||Takahashi - Mewlon 300CRS Dall-Kirkham Optical Tube Assembly|
|Additional Information||Optical Tube Assembly only|
|Aperture Ratio||f / 9.9|
|Batteries||4 x AA|
|Computer Hand Control||Focus and Fan control|
|Dew shield||Sold Separately|
|Focus System||Active Focus - power|
|Highest practical power||700x|
|Limiting Stellar Magnitude||14.2|
|Mount||NONE - OTA only|
|Optical Coatings||Fully Multi-coated|
|Optical Design||Corrected Dall-Kirkham|
|Optical tube diameter||12.75"|
|Optical Tube Length||41.14"|
|Optical Tube Weight||~60lbs|
|Secondary Mirror||95 mm|
|Star Diagonal||Sold Separately|
|Temperature Stability||3 fans|
|Tube Ring||Sold separately|