The Mewlon Series of Dall-Kirkham Telescopes by Takahashi
combines refractor-like performance in a larger folded optic reflector
design. The standard EM-200 or optional NJP mounts provide 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. The classical
Cassegrain telescope offers excellent performance, but they are
extremely expensive to produce at large apertures. By concentrating on
the Dall-Kirkham Cassegrains, the Mewlon telescope offers a professional
level of performance within reach of most amateurs.
Takahashi Mewlon employs 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.
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 and 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.
precision optical surfaces capable of delivering an airy disc of 20.
Because the Mewlon primary mirror is larger than the effective aperture,
its cell installation engineering helps to eliminate mirror stress
which can cause astigmatism. The focuser mechanism has also been
carefully designed to reduce shifting and maintain consistency. Both the
Mewlon 250mm and 300mm models come standard a secondary mirror
translating focuser that's accomplished with the electronic hand
controller. With a wide range of both visual and photographic
accessories available to the Takahashi Mewlon series, there is no reason
why you shouldn't be able to achieve any astronomy project you have in
mind using this fine telescope.
The 250mm and 300mm
Takahashi Mewlon electronic focusing is 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
facilitates 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.
the Mewlon series, it isn't necessary to sacrifice optical performance
for ease of use and portability. When it comes time to place your
Takahashi Mewlon telescope on a mount, it's as easy as simply connecting
the dovetail plates. The high quality finderscope not only lends itself
to the packages as an excellent instrument for alignment, but is also
designed as a convenient "grab handle" to assist in mounting and
transport. It's rigid construction means help in handling the optical
tube without fear of bending or breaking. On larger models, the Mewlon
also includes a counterweight against the body to help balance the
optical tube. Just these small considerations in Takahashi's Mewlon
design mean quality in engineering that sets it apart.
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.