CDK 700 - 28" Astrograph
The CDK700, a 0.7 meter, is a fully automated observatory class telescope and direct drive alt-azimuth mounting system designed and engineered by PlaneWave. PlaneWave is combining the revolutionary CDK optical design with an innovative direct-drive alt/az mount technology that sets a new standard for small observatory telescopes. More about the Optical Design.
With a 70mm image circle, the CDK700 is designed to excel at imaging on large format CCD cameras. The optical system utilizes a Nasmyth focus through both altitude bearings allowing your camera or eyepiece to remian at a fixed height while holding heavy instruments without needing to rebalance the optical tube assembly. Instrument can be installed on both sides of the fork mount and easily accessed using the included rotating tertiary mirror system. The Focusser / Image Rotator is available as an accessory with encoders for 20 kg instrument weight, as well as a larger version for instruments up to 60 kg.
With high-resolution encoders providing the feedback for the direct drive motors, not only will the telescope track without periodic error or have any backlash at all, but the mount will be able to counter against wind gusts. The direct drive motors can move the telescope at incredible speeds for tracking satellites or just to minimize target acquisition time.
The PlaneWave CDK700 is available in various types of mirror material. Standard mirror material is borosilicate. The telescope is also available in fused silica optics, Ritchey-Chrétien (RC) optics and infrared optimized.
Fused Silicia is a synthetic amorphous silica glass of the highest purity and one of the most transparent glasses made. The optical and thermal properties of fused silica are superior to other types of glass due to its purity. Its transmission and homogeneity exceed those of crystalline quartz without the problems of temperature instability inherent in the crystalline form. Fused Silica has a coefficient of thermal expansion six times lower than Borosilicate (Pyrex) glass, which means that as fused silica cools down, it preserves its shape to a high degree of accuracy. This translates into consistent optical performance and unchanging focus over temperature changes. With its high melting temperature ()~ 1.600 degree Celsius), a very low coefficient of thermal expansion and resistance to thermal shock, fused silica is the material of choice for professional observatories as well as various scientific applications.
- Pinpoint stars out to a 70mm image circle
- Direct-drive motors on each axis for smooth, fast, and virtually silent movement of the telescope. Direct Drive motors mean that there are no gears to cause backlash and periodic error
- High resolution encoders on each axis for precise positioning
- Incorporates PointXP mount modeling software by Dave Rowe All ASCOM compatible.
- Dual Nasmyth focus, allowing simultaneous mounting of two instruments or easy switching between visual and imaging use
- integrated rotator for the tertiary mirror, with magnetic locks to position the mirror precisely for either Nasmyth focus position. The rotator can move from one port to the other in under 10 seconds.
- Field de-rotator / rotational field framing
Benefits of Nasmyth Focus: The Nasmyth Focus is along the altitude axis so there are virtually no balancing issue as you change out equipment. Eyepieces remain at a constant wheelchair-accessible height, greatly simplifying access to the telescope for public observatories. The rotating tertiary mirror allows you to switch from one Nasmyth port to the other in just seconds, allowing observers to easily transition between imaging and visual use
To the left are two simulations showing the CDK's stunning performance. The first is a spot diagram and the second is a diffraction simulation. The spot diagram for 28" CDK optics on the optical axis, 21mm- and 35 mm off-axis.
The sqaures in the diagram are 9 micrometer (0.009 mm) wide.
For the CDK 700, a focusing unit is under devolopment, which also compensates the image field rotation in the Nasmyth Foki. The motor-driven focussing uses three guidances and toothed belts and is therefore "free from play and tipping". The rotation of the unit is realized by a worm gear transmission.
The figure shows the geometric dimensions of the CDK 700. The image center of the Nasmyth Foki is just under 1.2 m above the ground level
Pictures taken by CDK700":
Aperture 27.56 inch (700 mm) Focal Length 4540 mm Focal ratio 6.5 Central Obstruction 47% of the Primary Mirror Diameter Back Focus from Mounting Surface 309 mm (12.2 inch) Weight 1,200 lbs(544 kg) OTA Tube Dual truss structure with Nasmyth focus Optical Performance 1.8 micron RMS spots [25mm on-axis] (400 to 900nm) 4.4 micron RMS spots [21mm off-axis] (400 to 900nm) 6.8 micron RMS spots [35mm off-axis] (400 to 900nm) Dimensions 93.73" H x 43.25" W x 39" D Focus Position Nasmyth Focus Fully Baffled Field 60 mm Image Scale 22 microns per arcsecond Optimal Field of View 70 mm (0.86 degrees)
Fork Assembly Single piece U shaped fork arm assembly for maximum stiffness Azimuth Bearing 20 inch diameter thrust bearing Altitude Bearing 2 x 8.5 inch OD ball bearings Optical Tube Dual truss structure with Nasmyth focus
Motor Control Industrial grade Parker brushless motor control system and built in electronics Azimuth Motor Direct Drive 3 Phase Axial-Flux Torque Motor Altitude Motor Direct Drive 3 Phase Axial-Flux Torque Motor Encoder - Azimuth and Altitude 10 inch disk built into the azimuth and altitude axes with stainless steel encoder tape on the circumference with reader yields 16 million counts per revolution of the telescope. This translates to about 0.08 arcsecond resolution. Motor Torque Approximately 30 ft-lbs continuous; 60 ft-lbs peak Drive Electronics Capable of controlling up to 4 high speed encoders, limit switch inputs, homing switch inputs, controls two additional motors for accessories, two brake outputs and 16 digital and 2 analog inputs Telescope Control Software Incorporates PointXP mount modeling software by Dave Rowe All ASCOM compatible.
Pointing Accuracy 10 arcsecond RMS with PointXP Model Pointing Precision 2 arcsecond Tracking Accuracy System Natural Frequency 10 Hz or greater Field De-Rotator Accuracy 3 microns of peak to peak error at 35mm off-axis over 1 hour of tracking (18 arc sec)
Radius of Curvature 4115mm Optical Diameter 700 mm (27.56 inch) Outer Diameter 714.38 mm (28.125 inch) Core Diameter 203mm (8 inch) Material Precision Annealed Borosilicate or Fused Silica Edge Thickness 2.25 inch Cell 18 point
Radius of Curvature 2961 mm Optical Diameter 312.4 mm (12.3 inch) Outer Diameter 317.5 mm (12.5 inch) Core Diameter 203mm (8 inch) Material Precision Annealed Borosilicate or Fused Silica Thickness 25 mm Cell 3 point RTV
Optical Major Diameter 152.4 mm Material Precision Annealed Borosilicate or Fused Silica Thickness 25 mm
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