| Dall-Kirkham Cassegrain telescopes are known for their image quality, and the Takahashi Mewlon 300 is no exception. The hand-figured optics of its Dall-Kirkham design use a concave ellipsoidal primary mirror and a convex spherical secondary mirror to produce a long f/11.9 focal ratio. Its images are essentially 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 exceptional resolving power is more important than a wide field of view, such as lunar and planetary observation and imaging, resolving compact globular clusters, etc.
The Mewlon’s 310mm primary mirror is oversized compared to the scope’s effective 300mm aperture for brighter off-axis images. The primary mirror is fixed and focusing is done electrically by moving the secondary mirror fore and aft in its holder under the control of a supplied battery-operated hand control. A variable length focusing tube makes quick work of changing between a visual focus and one for astrophotography.
An optional 0.8x reducer/field flattener/corrector lens (#TMC1800) is available for the Mewlon. It converts the 300 from a 3572mm focal length f/11.9 system to a 2739mm focal length f/9.1. This increases the image circle from 25mm at the focal plane at f/11.9 to 42mm at f/9.1 with the reducer in place. The field of view is 45 arc minutes using the reducer.
The well-made aluminum optical tube has die-cast and machined metal front and rear cells. The rear cell has removable cooling vents on the sides and a removable back for faster cooling of the optics. The rear cell has both 1.25" and 2" accessory holders; an illuminated 11 x 70mm finderscope in a double ring mount; and a dual split ring mounting designed specifically for installing the heavy Mewlon 300 optical tube on a Takahashi equatorial mount.
The Takahashi Mewlon 300 measures a substantial 43" in length, 12.75" in diameter, and weighs 57.2 pounds, requiring the use of a high payload capacity mount, such as the Takahashi EM-400 or EM-500.
Features of the Takahashi Mewlon 300 Dall-Kirkham optical tube . . . - Dall-Kirkham Cassegrain optics: 300mm (11.8") aperture, 3572mm focal length, f/11.9 focal ratio, with removable rear cell and 196mm of available back focus. Hand-figured and diffraction limited 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. Additional knife-edge baffles within the body and the central baffle tube combine with the micro-grooves to very effectively prevent ambient light from reaching the image plane, thereby producing the dark sky background essential for high contrast, high magnification images.
- Removable cooling vents and rear cell cover: For faster cooling of the optics when the Mewlon 300 is first taken out for an evening’s observing or imaging, the rear cell cover is removable and there are removable cooling vents on the sides of the rear cell. Removing these exposes both the front and rear surfaces of the primary mirror to the air, reducing the optics cool down time without having to use a battery-powered fan as is the case with many sealed optical tubes. The side vents are held in place by chromed hinged catches. Removing the side vents exposes the front surface and edge of the primary mirror as shown in the feature images below. An aluminum collar around the Cassegrain focus holds the rear cell in place. Two bat wing handles on the collar make it easy to loosen and tighten the collar to remove and later reinstall the rear cell. Removing the shallow rear cell cover exposes the mirror back to the air, allowing air to flow over the entire mirror, front and back. Cool down time is typically on the order of 30 minutes, far faster than a closed tube system.
- Electric focusing: Unlike many Cassegrain scopes which focus manually by turning a knob to push the primary mirror fore and aft along the central baffle tube, the Mewlon 300 focuses electrically. The primary mirror is fixed. To focus, simply touch a button on the supplied hand control to command a motor to move the secondary mirror. A premium-grade Frauhaber Swiss single linear electric motor connected to the center of the secondary mirror holder smoothly moves the secondary mirror fore and aft in tiny increments for very precise focusing. The motor/secondary mirror assembly housing is mounted in a rigid four-vane spider. Together with the fixed primary mirror and the central drive of the secondary, the rigid spider assures that the Mewlon exhibits none of the image shift typical of a conventional Cassegrain as it is focused. The battery-operated hand control plugs into a receptacle under the rear cell of the scope.
- Variable drawtube and accessory holders: To make it easier and quicker to achieve a visual or photographic focus, the Mewlon has a variable drawtube focusing system for gross focus changes, in addition to the motor drive secondary mirror focuser for fine-tuning the focus. A 2" drawtube slides in and out of the rear cell. Its barrel has a focusing scale to let you switch quickly between predetermined approximate visual and photographic focus points. A large ribbed compression ring on the rear cell locks the variable drawtube in place when the proper rough focus is reached, allowing the electric focuser to make the final small adjustments. The variable drawtube terminates in a 2" accessory holder with two thumbscrews to hold accessories firmly in place. It can be used with a 2" star diagonal, 2" photo accessories, or 1.25" accessories using the supplied 1.25" adapter. The 1.25" adapter slips into the variable drawtube’s 2" accessory holder and uses a compression ring to hold optional 1.25" accessories (star diagonal, camera adapter, terrestrial image erecting diagonal, etc.) in place.
- Finderscope: A 11 x 70mm straight-through finderscope with a 4.2° field and interrupted crosshairs is standard equipment. A variable brightness battery-powered red LED illuminator lights up the finder’s crosshair. A sturdy dual ring finderscope bracket with collimation screws in both rings mounts on the scope’s rear cell.
- Mounting rings: The Mewlon 300 has a dual split ring tube holder with an accessory mounting plate/stabilizing spacer on top and a heavy duty mounting plate on the bottom. The four-hole mounting plate is designed specifically to mount the scope on a Takahashi EM-400 or EM-500 equatorial mount, the recommended mounts for use with this scope.
- Counterweight: The Mewlon 300 rings and mounting plate can only be positioned at one point along the Mewlon 300 body. They cannot act as a dovetail to let you move the scope fore and aft on an EM-400 or EM-500 mount to balance varying accessory loads. Therefore, a counterweight system is built into the Mewlon. This consists of a steel rail mounted under the optical tube. Two 3 pound (1.4 kg) counterweights with powerful built-in magnets fit onto the rail. The weights can be used singly or in combination. The magnets hold the counterweights in place, but allow them to be moved fore and aft on the rail to balance differing accessory loads. Thumbscrews lock the counterweights in place on the rail once the proper balance has been found.
|
Printer friendly version
Email page link to a friend
Do you have a question about this product?
Terestrial Photography
Lunar Photography
