Takahashi Mewlon-210 210mm f/11.5 Dall-Kirkham OTA

Product Overview

The Mewlon-210 is Takahashi's 210 mm Dall-Kirkham Cassegrain, sold as an optical tube assembly. At 2415 mm focal length and f/11.5 in a 700 mm tube, 244 mm across, it steps up from the Mewlon-180C in aperture and reach while keeping the same concave ellipsoidal primary and spherical secondary design. Weight is 8.1 kg, and focusing moves the primary mirror rather than a rack-and-pinion drawtube.

Who It's For

This is a good match if you want more aperture and a longer native focal length than the 180C for high-resolution lunar, planetary and double-star observing, or for imaging small targets — galaxy cores, planetary nebulae — where 2415 mm, or 1961 mm at f/9.3 with the M-FLRD reducer, resolves detail a shorter refractor cannot. Visual observers get a bigger aperture's light grasp and resolving power in a tube that still travels to a dark site.

If wide-field nebula or Milky Way framing is the goal, this tube's narrow native field is the wrong tool — a fast refractor covers that ground instead. Tell us what you are observing or imaging and we will confirm the fit.

Key Features & Design

• Dall-Kirkham Cassegrain optics: a concave ellipsoidal primary and spherical secondary, with negligible on-axis coma.
• 2415 mm at f/11.5: in a 700 mm tube, 244 mm across — 210 mm of aperture's worth of reach beyond the 180C.
• Primary-mirror focusing: the focal point moves by translating the primary, extending the back focal length by about 160 mm.
• 8.1 kg: heavier than the 180C, and worth checking against your mount's payload once a diagonal or camera is attached.
• 67.2 mm of back focus at prime focus, measured from the rear of the 50.8 mm adapter.
• M-FLRD reducer compatible: brings the system to 1961 mm at f/9.3, a 30 mm image circle, at 56.2 mm back focus.

Optical / Mechanical Design

The Mewlon-210 shares its optical formula with the 180C at larger scale: a concave ellipsoidal primary paired with a spherical secondary, which is easier to figure precisely than the hyperbolic secondary a Ritchey-Chrétien needs and keeps on-axis coma negligible. The tradeoff is the same — off-axis field curvature that suits the narrow, high-power field of planetary and lunar work rather than a wide astrograph field.

Focusing moves the primary mirror internally instead of extending a drawtube, sealing the optical path against dust and reducing focus-induced image shift. The M-FLRD focal reducer/flattener converts the system to 1961 mm at f/9.3 with a 30 mm corrected circle and 56.2 mm of back focus, shortening the reach for imaging where 2415 mm at f/11.5 is longer than the target calls for.

Recommended Uses

• Lunar and planetary observing: at 2415 mm and f/11.5, with the resolving power a 210 mm aperture provides.
• Double star splitting: long focal length and a well-corrected on-axis image favour close, faint pairs.
• High-resolution imaging of small targets: galaxy cores and planetary nebulae at native focal length, or 1961 mm at f/9.3 with the M-FLRD reducer.
• Visual deep-sky observing: the aperture gathers more light than the 180C for fainter targets at moderate power.

Compatibility and Accessory Notes

Back focus at prime is 67.2 mm from the rear of the 50.8 mm adapter, narrowing to 56.2 mm with the M-FLRD reducer fitted — tighter than most apochromatic refractors, so a long camera or filter-drawer stack may not reach focus without adjustment. Our Takahashi Back Focus Guide collects these figures for the whole Takahashi range, and the Mewlon-210's own system chart in the Downloads tab lists the exact parts and distances per configuration.

• Reducer/flattener: the M-FLRD is sold separately and is the listed conversion accessory for this tube.
• Mount: sold as an OTA — no mount, dovetail, diagonal or eyepiece included. At 8.1 kg before accessories, a mount rated for 12–15 kg of total payload is a reasonable starting point once a diagonal, camera and finder are added.
• Finder and dovetail: a compatible finder bracket and dovetail plate are separate purchases for this tube.

If you are not sure your camera reaches the 67.2 mm or 56.2 mm back focus figures, send us your imaging train and we will work out the spacing with you.

Good to Know Before You Order

• This is an optical tube assembly. Mount, dovetail, diagonal, eyepiece and finder are all sold separately.
• At 8.1 kg, mount payload is worth checking early. Add the weight of a diagonal, camera and finder before matching it to a mount.
• Back focus is tighter than a typical refractor. 67.2 mm at prime, 56.2 mm with the M-FLRD reducer — the system chart in the Downloads tab lists the parts for each configuration.
• Native field is narrow. At f/11.5 the corrected field suits planetary and lunar targets; the M-FLRD reducer widens it to a 30 mm circle at f/9.3.

Frequently Asked Questions

Is it difficult to set up?

No. It arrives collimated from the factory, and primary-mirror focusing means there is no separate rack-and-pinion focuser to adjust before first light. Occasional collimation touch-ups are normal Cassegrain maintenance and quick with a collimation eyepiece.

What is it best used for?

High-resolution lunar and planetary observing, double star splitting, and imaging small targets — galaxy cores and planetary nebulae — at long focal length.

Does it come with a mount?

No. It ships as an optical tube assembly. Mount, dovetail plate, diagonal and eyepiece are separate purchases.

What mount does it need?

At 8.1 kg before accessories, a mount rated for roughly 12–15 kg of total payload once a diagonal, camera and finder are attached is a reasonable starting point. Tell us your mount model and we will confirm.

How is this different from the Mewlon-180C?

Aperture and focal length. The 210 has a larger primary, more light grasp and a longer native focal length; the 180C is lighter and slightly more portable.

When should this not be the choice?

For wide-field nebula or Milky Way imaging, where a fast, short-focal-length refractor frames the target better than this tube's narrow native field.

Bottom Line

In short: a 210 mm Dall-Kirkham Cassegrain OTA at 2415 mm and f/11.5 — 1961 mm at f/9.3 with the M-FLRD reducer — weighing 8.1 kg, with 67.2 mm of back focus at prime to work into an imaging or visual train. It is built for high-resolution work on the Moon, planets and double stars, and for detail on small deep-sky targets.

Optical Diagram Reports

Takahashi publishes a spot diagram for the Mewlon-210 at prime focus, showing star images across the field at the design wavelengths.