Orion Optics UK ODK10 Optical Tube Assembly

ODK f/6.8 Optical Design: 250mm Aperture and 1700mm Focal Length

The heart of the ODK10 is its Corrected Dall-Kirkham optical system. This design uses a 250mm primary mirror to achieve a 1700mm focal length, striking a balance between wide-field deep-sky imaging and high-resolution planetary work. The native f/6.8 focal ratio is significantly faster than standard Schmidt-Cassegrains, allowing you to collect more light in less time and reduce total exposure duration for faint targets.

Full-Frame Imaging: A 50mm Flat Field with 6.2μm Edge Spots

Unlike conventional reflector designs that suffer from off-axis coma, the ODK10 incorporates a multi-coated 3-lens corrector to produce a natively flat 50mm image circle. This is large enough to accommodate full-frame (35mm) sensors without vignetting or distortion. The optical correction is superb, yielding tight, round stars with a spot size of just 6.2μm at the very edge of the field, ensuring your images are sharp from corner to corner.

Thermally Stable Engineering: Carbon Fibre Tube and 3 Cooling Fans

Focus stability is critical for long-exposure astrophotography. The ODK10 addresses this with a carbon fibre sandwich tube that exhibits virtually zero thermal expansion, preventing the focal plane from shifting as ambient temperature drops. Weighing approximately 12kg and measuring only 530mm long, the open-tube design is further enhanced by three controllable fans behind the primary mirror, ensuring rapid thermal acclimation and minimizing tube currents.

Heavy-Duty Imaging Train: 3" Focuser and 213mm of Back Focus

The ODK10 is built to carry modern imaging loads. It features a robust 3" Crayford focuser with a 10:1 fine reduction knob for precise focus adjustments, even with heavy equipment. An exceptionally generous 213mm of back focal distance provides ample room to install complex imaging trains, including off-axis guiders, large filter wheels, and camera rotators, without running out of focus travel.

ODK10 vs. a 10" SCT: The Benefits of a Corrected Astrograph

While a 10" Schmidt-Cassegrain Telescope (SCT) is a capable instrument, the ODK10 offers distinct advantages for the serious imager. The SCT's primary mirror focusing can introduce image shift, a problem eliminated by the ODK10's fixed mirror and external focuser.

• Native Speed and Field: The ODK10's native f/6.8 is faster than a typical f/10 SCT, reducing exposure times. More importantly, its 50mm corrected flat field is built-in, whereas an SCT requires an additional, expensive reducer/corrector to achieve a similar result.
• Thermal Management: The ODK10's open tube and three cooling fans allow it to reach thermal equilibrium much faster than a closed-tube SCT, resulting in sharper images sooner.
• Back Focus: With 213mm of back focus, the ODK10 easily accommodates more accessories than most standard SCTs, providing greater flexibility for your imaging setup.