PLANEWAVE CDK700 OBSERVATORY SYSTEM

 

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PlaneWave Instruments brings a fully automated observatory class telescope to the market with the CDK700, a 0.7 meter Alt-Az telescope system, combining the revolutionary CDK optical design that founded PlaneWave Instruments with an innovative direct-drive alt/az mount technology that sets a new standard for small observatory telescopes.

CDK700 Features

• Pinpoint stars out to a 70mm image circle
• Ultra-low thermal expansion fused silica optics
• Dual Nasmyth focus, allowing simultaneous mounting of two instruments or easy switching between visual and imaging use
• Direct-drive motors on each axis for smooth, fast, and virtually silent movement of the telescope
• High resolution encoders on each axis for precise positioning
• Zero backlash
• Zero periodic error
• PointXP mount modelling software
• Field de-rotator / rotational field framing

 An alt/az mount is inherently more stable than an equatorial mount since there is no cantilevered mass, nor are there any large protruding counterweights to create a dangerous hazard in a public observatory. An alt/az telescope is also considerably more compact than its equatorial counterpart, allowing a larger telescope to fit in a smaller enclosure. The mass it takes to make a rigid alt/az mount is substantially less, leading to cost savings.

Unlike German Equatorial mounts, there are no meridian flips to deal with. You can image from horizon to horizon continuously if desired. Alt/Az is more intuitive to use and no polar alignment is needed. Besides, it is the way the professionals do it!

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.

Rotating tertiary mirror

The CDK700 includes an 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.

Direct drive motors and encoders

Direct Drive motors mean that there are no gears to cause backlash and periodic error. 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.

All PlaneWave telescopes feature the following ports for dew heater and fan management:

• Two RCA connectors to power the dew heater (from the Delta T or from a 12V source)
• One RJ connector for the Delta T to the telescope to transmit temperature data
• One EFA connector to power the fans (EFA to 5.5-2.1 jack included)
• One auxiliary output port

The built-in dew heaters can be powered by any 12V DC source which has an RCA connector, but the Delta T is required to keep the mirror just above the dew point to avoid overheating and the resulting internal turbulences.

The EFA connector can be powered by the separate EFA controller, any 12V DC source using the supplied EFA to 5.5 x 2.1 jack, or by the Series-5 controller.

Optics

 

Optical system

Aperture	700 mm (27.56")
Focal length	4540 mm
Focal ratio	f/6.5
Central obstruction	47% of the primary mirror diameter
Backfocus from mounting surface	309 mm
Optical performance (400-900 nm)	1.8μ RMS at 25 mm on-axis; 4.4μ RMS at 21 mm off-axis; 6.8μ RMS at 35 mm off-axis
Image scale	22μ per arcsecond
Optimal field of view	70 mm image circle
Construction	Dual truss structure with Nasmyth focus
Fully baffled field	60 mm
Weight	544 kg
Dimensions	93.73″ H x 43.25″ W x 39″ D

Primary mirror

Optical diameter	700 mm
Outer diameter	714.38 mm
Material	Fused silica (quartz)
Core diameter	203 mm
Edge thickness	57.15 mm
Radius of curvature	4115 mm

 

Secondary mirror

Optical diameter	312.4 mm
Outer diameter	317.5 mm
Material	Fused silica (quartz)
Thickness	25 mm
Cell	3 point RTV
Radius of curvature	2961 mm

 

Tertiary mirror

Optical major diameter	152.4 mm
Thickness	25 mm
Material	Fused silica (quartz)

 

Mechanics

Mechanical structure

Fork assembly	Single piece U shaped fork arm assembly for maximum stiffness
Azimuth bearing	20" diameter thrust bearing
Altitude bearing	2 x 8.5" OD ball bearings
Optical tube	Dual truss structure with Nasmyth focus

 

Motion control

Motor control	Industrial grade Parker brushless motor control system and built in electronics
Motors	Direct Drive 3 Phase Axial-Flux Torque Motors
Encoders	10 inch disk built into both axes with stainless steel encoder tape on the circumference with reader yields 16 million counts per revolution of the telescope. 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 analogue inputs
Control software	Incorporates PointXP mount modelling software by Dave Rowe All ASCOM compatible.

 

System performance

Pointing accuracy	10 arcsecond RMS with PointXP Model
Pointing precision	2 arcsecond
Tracking accuracy	<1 arcsecond error over 10 minute period
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 arcsec)