Orion Optics UK ODK16 Optical Tube Assembly

400mm f/6.8 Optics: A >52mm Flat Field for Large Format Sensors

The heart of the ODK16 is its corrected Dall-Kirkham optical system. The 400mm primary mirror gathers immense light, while the f/6.8 focal ratio allows for shorter exposure times on faint nebulae compared to slower designs. A factory-matched, multi-coated 3-lens corrector is permanently integrated into the optical path, eliminating the need for third-party flatteners and ensuring the system performs to its full potential.

This design produces a corrected image circle greater than 52mm, fully illuminating the largest full-frame CMOS and CCD sensors without vignetting or field curvature. With spot sizes as small as 2.4µm, you can leverage the resolution of modern high-pixel-density cameras to capture incredibly sharp, detailed images across the entire frame.

Zero-Expansion Carbon Tube: Thermal Stability Across a 835mm Tube

To maintain precise focus during temperature drops, the ODK16's 835mm tube is constructed from a carbon fibre sandwich material. This advanced composite has virtually zero thermal expansion, preventing the focal plane from shifting during long imaging sessions or throughout the night. The result is consistently sharp stars without the need for constant refocusing.

The open-tube design, combined with three controllable fans behind the honeycomb CNC-machined primary mirror cell, ensures rapid thermal acclimation. This active cooling system quickly brings the 400mm mirror to ambient temperature, minimizing tube currents and delivering stable, high-contrast views sooner.

Imaging Integration: 216mm of Back Focus and a 3" Crayford

The ODK16 is built from the ground up for serious astrophotography. It provides a generous 216mm of back focal distance measured from the rear of the mirror cell, offering ample room for complex imaging trains. You can easily accommodate off-axis guiders, large filter wheels, rotators, and adaptive optics systems without concern for reaching focus.

Focusing is managed by a robust 3" Crayford focuser, featuring 10:1 fine reduction for critical adjustments. This large-aperture focuser provides a rigid, flexure-free connection point for heavy camera packages, ensuring the optical axis remains perfectly aligned throughout your exposure.

ODK16 vs. Ritchey-Chrétien: The Advantage of an Integrated Corrector

While Ritchey-Chrétien (RC) telescopes are known for their coma-free fields, they typically operate at f/8 or slower and require a separate, often expensive, field flattener or reducer to produce sharp stars on large sensors. The ODK16's primary advantage is its fully integrated, optimized optical system.

• Built-in Correction: The ODK16's 3-lens corrector is designed as part of the optical train, not an add-on. This guarantees a >52mm flat field out of the box, with performance optimized for its native f/6.8 focal ratio.
• Faster Imaging: At f/6.8, the ODK16 requires significantly less exposure time to reach the same signal-to-noise ratio as a comparable f/8 RC, allowing you to gather more data in a single night.
• No Spacing guesswork: With an integrated corrector, you avoid the trial-and-error of finding the perfect corrector-to-sensor spacing that is often required with third-party accessories on an RC.