0.7m CDK Telescope System (CKD700)

0.7m CDK Telescope System

Part   CDK700

PlaneWave Instruments now brings a fully automated observatory class telescope to the market in the CDK700, a 0.7 meter, Alt-Az telescope system. We are combining the revolutionary optical system that founded PlaneWave Instruments with a brand new innovative alt/az mount technology that sets a new standard for small observatory telescopes.

CDK700 Features

• Pinpoint stars out to a 70mm image circle
• Dual Nasmyth focus
• Direct drive motors on each axis
• Hi Res Encoders on each axis
• Zero backlash
• Zero periodic error
• PointXP Mount Modeling Software
• Field de-rotator / field framing
• Stiff, smooth, quiet and extremely fast drive system

An alt/az mount is inherently more stable than an equatorial mount as there is no cantilevered mass, nor are there any large counterweight protruding that are very dangerous in a public observatory. The mass it takes to make a rigid Alt/Az mount is substantially leading to cost savings. There is no dealing with balance changes as you cross the meridian or meridian flips that German Equatorial Mounts have to deal with. You can image from horizon to horizon continuously if desired. Alt/Az is more intuitive to use and there is no polar alignment needed. Besides, it is the way the big boys 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. In addition the CDK700 comes standard with a field rotator / field framer.

Direct drive motors and encoders: Direct Drive motors means that there are no gears which cause backlash and periodic error. With the 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.

CDK Optical Design: Our design produces a flat, coma free and astigmatic free field of view. Since the secondary mirror is spherical, centering is very forgiving (which means it is easy to get the telescope optics aligned for optimum performance, this is not the case for most high-end astrographs) The end result at the image plane of the CDK design is no off-axis coma, no off-axis astigmatism, and a perfectly flat field, all the way out to the edge of a 50mm image circle.  All this means, the stars will be pinpoints from the center of the field of view out to the corner of the field of view.

Features and Specifications

Optical System

Optical Design	Corrected Dall-Kirkham (CDK)
Aperture	700 mm (27.56 inch)
Focal Length	4638 mm
Focal ratio	f/6.6
Central Obstruction	42% of the Primary Mirror Diameter
Back Focus	305 mm (12 inch) from Mounting Surface
Focus Position	Nasmyth Focus
Usable Field of View	70 mm (0.86 degrees)
Fully Baffled Field	60 mm
Image Scale	22 microns per arcsecond
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) Spot Diagram

Mechanical Structure

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

Motion Control

Motor Control	Sideral Technology 3 phase 24 V AC brushless motor controller. Telescope mount modeling software included optimal pointing and tracking accuracy.
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 35 ft-lbs
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
SiTech Telescope Control Software	Incorporates PointXP mount modeling software by Dave Rowe and SiTech’s control software. All ASCOM compatible.

Standard Features

Point XP Modeling Software	Telescope mount modeling software included for optimal pointing and tracking accuracy.
SiTech Control Electronics	Controls the motion of the telescope, the field de-rotator and the focuser
Focuser	Large aperture, heavy-duty focuser can handle large payloads and will not add vignetting. The focuser is motor controlled and is ASCOM compatible
Field De-Rotator / Image Framer	Built in field de-rotator and image framer
Cooling Fans and Temp Sensors	Multiple cooling fans and multiple temperature sensors for monitoring and equilibrating the primary mirror

System Performance

Pointing Accuracy	10 arcsecond RMS with PointXP Model
Pointing Precision	2 arcsecond
Tracking Accuracy	1 arcsecond error over 3 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 arc sec)

Primary Mirror Blank Spec

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	Pyrex or Borosilicate Precision Annealed
Edge Thickness	2.25 inch
Cell	18 point

Secondary Mirror Blank Spec

Radius of curvature	2961 mm
Thickness	38.1 mm
Optical Diameter	270 mm
Outer Diameter	280 mm
Cell	3 point RTV

Tertiary Mirror Blank Spec

Optical Major Dia	152.4 mm
Thickness	25 mm

NOTE: All specifications and dimensions are subject to change. And we do expect small changes in many of the specifications.

The CDK (Corrected Dall-Kirkham) Optical Design is an innovative solution for unsurpassed astroimaging quality at an affordable price. The CDK telescope design provides excellent imaging with large format CCD cameras while remaining superb for visual use. The CDK design far exceeds the off-axis performance of most commercial telescope designs including the Ritchey-Chrétien design.

This no-compromise design is unique in making the optical alignment forgiving and collimation very easy. This guarantees the user the best possible performance from the telescope. The end result at the image plane of the CDK design is no off-axis coma, no off-axis astigmatism, perfectly flat field (no off-axis defocus). The CDK design will give you pinpoint stars from the center to the corner of the field of view.

The CDK Optical Design