Takahashi Dall-Kirkham Optical Tubes

More Information  · Recommended Accessories  · Images of Some Features Price $3,129.00 List Price $3,699.00 Highest Useful Magnification 403x Focal Length 2415mm Focal Ratio f/11.5 Resolution 0.55 arc seconds Visual Limiting Magnitude 13.4 Aperture 8.3" Weight 17.6 lbs. Warranty 5 years

Dall-Kirkham Cassegrain telescopes are known for their image quality, and the Takahashi Mewlon 210 is no exception. The Dall-Kirkham design uses a concave ellipsoidal primary mirror and a convex spherical secondary mirror to produce a long f/11.5 focal ratio, with images that are free from astigmatism, although at the expense of greater off-axis coma than a conventional reflector. While this limits its field of view, it provides exceptionally sharp images on-axis. The field is very dark, with pinpoint star images and an excellent contrast range. This makes the Dall-Kirkham design particularly well-suited to observations where good resolving power is more important than a wide field of view, such as lunar and planetary observation, resolving compact globular clusters, etc.

The Mewlon’s 220mm primary mirror is oversized compared to the scope’s effective 210mm aperture for brighter off-axis images. The mirror is mounted on a thimble that slides fore and aft on the primary mirror baffle tube to focus the scope. A large focusing knob is located at the 3 o’clock position on the rear cell. The center-supported mirror cell is designed to avoid the stresses that sometimes generate astigmatism in conventional mirror cells.

An optional 0.8x reducer/field flattener/corrector lens (#TMC1800) is available for the Mewlon. It converts the 210 from a 2415mm focal length f/11.5 system to a 1961mm focal length f/9.3. This increases the image circle from 18mm at the focal plane at f/11.5 to 39mm at f/9.3 with the reducer in place. The field of view is 1.2° using the reducer.

The well-made aluminum optical tube has a die-cast and machined metal rear cell. The rear cell has a large helical focusing knob for very precise focusing; both 1.25" and 2" accessory holders; a 7 x 50mm finderscope in a very robust mount that doubles as a carrying handle for the scope; and a dovetail rail for attachment of the tube to the supplied offset dovetail adapter for mounting on a Takahashi EM-11 or EM-200 equatorial mount. The Takahashi Mewlon 210 measures 27.5" in length, 9.6" in diameter, and weighs a very reasonable 17.6 pounds.

Features of the Takahashi Mewlon 210 Dall-Kirkham optical tube . . .

• Dall-Kirkham Cassegrain optics: 210mm (8.3") aperture, 2415mm focal length, f/11.5 focal ratio, with 152mm available back focus. Ellipsoidal primary mirror and spherical secondary mirror. The mirrors are coated with highly reflective enhanced aluminum and overcoated with quartz for long life.

• Fully-baffled optics: The interior of the aluminum optical tube in finished in a non-reflective matte black. The front rim of the optical tube curves inwards to form a highly effective knife-edge baffle at the front of the body. The secondary mirror light baffle is micro-grooved on its interior to shield the mirror from stray light for higher contrast. The first 20% of the primary mirror baffle tube interior is likewise micro-grooved to improve contrast. The remaining 80% of the baffle tube contains 12 knife-edge baffles machined into its interior. This combination of micro-grooves and knife-edge baffles is very effective at preventing ambient light from reaching the image plane, thereby producing the dark sky background essential for high contrast, high magnification images.

• Focuser: A large rubber-clad focusing knob on the rear cell moves the primary mirror back and forth along the central baffle tube to focus the scope. Focusing is slow, but very precise. Once focused on a celestial object however, changing the focus to another sky object will not take much time or effort, however. Only a turn or two of the focusing knob will suffice to move the sharp focus from the terminator of the Moon to a star cluster thousands of light years away, for example.

• Finderscope: A 7 x 50mm straight-through finderscope with a 6.3° field and interrupted crosshairs is standard equipment. The finderscope bracket is exceptionally robust and rigid, allowing it to be used as a carrying handle for the optical tube with little danger of knocking the finder out of collimation. An optional battery-powered red LED crosshair illuminator can be threaded into the finderscope, if desired.

• Accessory holders: Two accessory holders are supplied for use with the Mewlon 210. One is a 2" accessory holder that threads onto the rear cell of the scope and can be used with a 2" star diagonal or 2" photo accessories. It has two thumbscrews to hold accessories firmly in place. The second slips into the 2" adapter and holds optional 1.25" accessories (star diagonal, camera adapter, terrestrial image erecting diagonal, etc.) It uses a compression ring to hold accessories.

• Mounting dovetail: The Mewlon 210 has an attached dovetail rail for mounting the scope quickly and directly onto a supplied dovetail adapter. The dovetail adapter fits Takahashi EM-11 and EM-200 equatorial mounts and has an offset design that helps to very effectively balance the Mewlon optical tube on these mounts.