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The ODK-Series (Optimised Dall-Kirkhams) is based on a focal ratio of f/6.8, fast enough for some superb deep sky photo-visual use and, still have enough focal length for high resolution planetary work both visual and CCD applications.
The tube is constructed from Carbon Fibre sandwich design. Very, very strong to avoid flexing and, zero expansion to ensure the focal plane does not change over long photographic exposures. Being an open tube design and very short, cool down times are remarkably fast.
To assist cool down of the telescope, each model is fitted with three fans, all positioned behind the primary mirror.
Exact focusing across the ODK range is achieved with the ACU-3S 3”-Crayford Focuser featuring a 10:1 reduction drive.
Good images need good optics, all fitted in reliable, stable and precise engineering.
The primary mirror is made from Schott Borosilicate Low Expansion Suprax glass (virtually identical to Pyrex). The mirror is produced to exacting standards to an F/4 paraboloid configuration. It achieves a surface accuracy of 1/6 wave or better. Orion Optics UK use one of the worlds most exacting measuring devices, a Zygo Laser Interferometer. It can measure optical distances which are smaller than 2,000, yes, 2,000 times smaller than the thickness of a human hair.
Without a Zygo or similarly accurate and reliable measuring instrument, it is impossible to give accurate measurements of an optics’ or telescope’s performance. Only the best manufacturers in the business of making telescopes use them because they are not suitable for mass produced telescopes, they are slow to use and need highly skilled technicians to operate them, it just does not lend itself to anything other than the highest quality, hand figured optics, definitely not mass produced optics to a tight budget.
The primary mirror is Hilux coated for the highest possible aluminium protected reflective surfaces available.
Tube Rings: To give maximum security and exactness, Orion Optics UK manufacture on their own CNC milling machines, aluminium tube rings which are machined from solid pieces of aluminium and later black anodised to protect the surface which are felt lined to give a gentle but firm grip to the polished tubes. Pressure adjustment is made by the large knurled knob on each tube ring to give precise amounts of friction on the tube outer surface.
ACU-3S: The ODK series of Optimised Dall Kirkhams is supported by a precision 3” focuser of short draw tube length. The top of the draw tube is threaded to accept many accessories, adaptors and spacing componenets. Silky smooth, incredible strength and attractive looks give you all the reliability and confidence in the ACU-3S you are ever likely to need. 3” internal threaded draw tube (76.2mm) enables wide fields to be achieved with vignetting not being a problem. Ultra accurate 10:1 slow motion control with a smooth, effortless motion which has got to be tried to be believed. Carrying capacity way beyond the requirements of all but the heaviest cameras.
The focuser is connected to the telescope by means of a very accurate machined female dovetail which is held onto a male equivalent on the telescope tube or cell with stainless steel grub screws. The beauty of this arrangement is that these screws and dovetail coupling allow you to rotate the focuser through 360 degrees rotation. In other words, to put it in exactly the rotational position you want for the attached equipment fitted, CCD, filter wheels, guiders etc. It just makes it so easy to set things up perfectly to meet your needs.