Takahashi - Mewlon 250 Dall-Kirkham
OTA
- The Mewlon combines refractor-like performance in a larger folded optic
reflector design.
- The 250 optical tube assembly has 9.8" of aperture and a focal ratio of 12.
- Comes with Fraulhaber German electric focus motor for secondary (no image shift!)
- OTA includes 7X50 finder, dovetail holder, and tube weight.
- Photo shows optional mount and tripod not included.
The Mewlon Series of Dall-Kirkham Telescopes by Takahashi© combines refractor-like
performance in a larger folded optic reflector design.
The EM-200 mount (sold separately or in the Mewlon-250US System Package) provides a
stable, accurate platform for the M-210. The integral polar alignment telescope and R.A. axis level
make accurate polar alignment to within 2 arc minutes of the celestial pole quick and easy. The reticle
is designed to be used in either Hemisphere until the year 2030. No other manufacturer uses such a
highly accurate polar telescope.
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 Mewlon 250 weighs only 28lbs (12.7kg) and is remarkably compact for a 10" Cassegrain.
This instrument is highly portable and offers 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.
Mewlon - 250 Dall-Kirkham OTA Specifications
- Effective aperture: 250mm
- Focal length: 3000mm / 2307mm w/ reducer
- Focal ratio: f/12-f/9.2 w/ reducer
- Resolution: 0.46"
- Limiting magnitude: 13.8
- Light grasp:1275x
- Image circle: 21mm / 42mm w/ reducer
- Photographic field: 1.0 degree w/ reducer
- Total length of main tube: 850mm
- Diameter of main tube: 280mm
- Primary mirror: 260mm f/3
- Seondary mirror: 72mm / x4
- Finder scope: 7x50 6.3 degree
- Gross wt. of main tube assembly: 12.5kg (27.5lb)
