PlaneWave CDK400 17-inch f/6.8 Telescope and L-500 Mount Observatory Telescope System
- Complete observatory system comprising a CDK17 f/6.8 Astrograph with fused Silica optics and PlaneWave L-500 alt-az mount
- CDK17 has 70 mm field of view without any field curvature, off-axis coma, or astigmatism
- Carbon-fibre truss tube design
- The L-500 mount can hold payload of over 91 kg (200 lbs) for CDK17 with accessories
- Mount has zero backlash and zero periodic error
- Integrated high resolution encoders
- Incredible slew speed up to 50 degrees per second
This PlaneWave observatory telescope system comprises
- PlaneWave CDK17 OTA with fused Silica optics
- PlaneWave L-500 direct drive alt-az mount
PlaneWave's CDK17 is a 17-inch (0.43 m) aperture f/6.8 telescope that is very well suited for astro-imaging as well as for visual use. The CDK17 telescope utilises the Corrected Dall-Kirkham (CDK) optical design, developed by Dave Rowe, that provides excellent imaging possibilities 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 making the CDK an innovative solution for unsurpassed astro-imaging quality at an affordable price.
At the image plane of the CDK17, will give you pinpoint stars from the centre to the corner of its 70mm field of view without any field curvature, off-axis coma, or astigmatism. The no-compromise optical design is unique in making the optical alignment forgiving and collimation very easy which guarantees the user the best possible performance from the telescope.
The CDK17 features a dual carbon-fibre truss design, with 3 cooling fans blowing air throughout the back of the telescope with 4 fans blowing air over the mirror to help it cool. The instrument weighs 48kg (106 lbs) and comes as standard with a back plate retaining ring ready to accept the focuser of your choice. The telescope comes with fused Silica optics as standard.
The PlaneWave L-500 mount: is an alt-azimuth, single-fork arm style mount that is capable of carrying a total payload of 91kg/200lbs and therefore can easily carry a PlaneWave CDK17 and accessories (e.g. CCD Camera etc). The mount uses a direct drive motor system with high resolution encoders on both the RA and DEC axes that results in zero backlash and periodic error. The mount can slew at speeds from 20 degrees to up to 50 degrees per second!
The mount combines versatility, simplicity and affordability by combining all the technology of PlaneWave's Observatory-class telescopes into a compact and stand-alone mount and is a breakthrough in mount design, specification and features for the price.
The CDK17 telescope is an open truss tube design for a rigid, but lightweight structure, and for quick thermal cooling. The truss tube utilises a carbon fibre frame which minimises thermal expansion that can cause focus shift with changes in temperature. The carbon fibre truss tube design also promotes quick thermal cooling.
To create the telescope's baffles, Planewave uses digital 3D printing technology. Their 3D printers add successive layers of material to construct a baffle system with precision. These internal stray light baffles minimise vignetting and maximise image contrast.
To mount the CDK17 onto a mount, PlaneWave supplies the CDK with a dovetail bar. The CDK features a dovetail expansion joint that allows for the difference in thermal expansion between carbon fibre and aluminium. This expansion joint allows the aluminium dovetail expand and contract without stressing the carbon fibre lower truss.
For dew prevention, the CDK17 is internally wired with polyimide film heater pads and temperature sensor, ready to be controlled with the optional Delta-T controller.
To help the primary mirror to cool, three cooling fans eject air from the back of the telescope and four fans blowing across the boundary layer of the mirror surface. This helps the telescope to reach thermal equilibrium quickly. The fans can be controlled by a computer if the optional Electronic Focus Accessory (EFA Kit) is purchased.
The Ritchey Chrétien (RC) optical design has long been "the standard" in high end imaging telescopes due to its use in many professional observatories. The RC is successful in eliminating many of the problems that plague many other optical designs, namely off-axis coma, however the RC design does nothing to eliminate the damaging effects of off-axis astigmatism and field curvature. The RC design is also very difficult, and therefore expensive, to manufacture and optically align.
The CDK design tackles the "off-axis coma problem" by integrating a pair of correcting lenses into a two mirror design. The beauty is that this design also corrects for astigmatism and field curvature. Because the lenses are relatively close to the focal plane (unlike the Schmidt corrector plate found in various Schmidt Cassegrain designs), and because these lenses work together as a doublet, there is no chromatic aberration. The CDK offers a wide aberration-free, flat field of view that allows the user to take full advantage of the very large imaging chip cameras in the market place today.
Having an aberration free telescope design means nothing if the optics cannot be aligned properly. Many Ritchey owners never get to take full advantage of their instrument’s performance because the Ritchey is very difficult to collimate. Aligning the hyperbolic secondary mirror’s optical axis to the optical axis of the primary mirror is critical in the Ritchey design, and the tolerances are unforgiving. The secondary mirror of the CDK design is spherical. It has no optical axis and so the centering tolerance of the CDK secondary mirror is comparatively huge. With the help of some very simple tools, the CDK user will be able to set the secondary spacing, collimate the optics and begin enjoying the full performance potential the instrument has to offer within a few minutes.
Below are a few images (M81 top; Veil nebula bottom) taken with a CDK17 to show how well they perform.
The PlaneWave L-500 features Direct Drive motors and on-axis encoders on both the RA and DEC axes. This eliminates the need for gear-based mechanics, thereby eliminating backlash and periodic error. With the high-resolution encoders providing feedback for the direct drive motors, not only will the telescope track without periodic error and backlash, the mount will also counter wind gusts with precise servo feedback.
The L-series direct drive motors can move the telescope at speeds from 2 degrees and up to 50 degrees per second. This makes the mount ideal for tracking satellites or just minimising celestial target acquisition time.
The PlaneWave 8"-wide dovetail mounting bracket holds telescopes onto the inside of L mounts fork arm. An additional dovetail clamp is available to allow the mounting of an extra supplementary telescope on the outside of the fork arm adding to the mount's versatility.
Adding extra accessories to a single-mounted telescope, or adding a second telescope can affect the overal balance of the whole telescope. The upper portion of the L mount can be moved horizontally for precise centre-of-gravity balancing whether the mount is in Alt-Az or Equatorial configuration.
To keep cabling from e.g. CCD cameras, filter wheels etc, the L- series mounts feature interior "through-the-mount" cable routing via access panels in the fork arm and azimuth axis sections.
The PlaneWave alt-az L-Series uses the same proven technology as used in the well-respected CDK700 telescopes which are being used in Universities such as the UK's University of Central Lancashire Alson Observatory >>HERE<<.
|Optical Design||Corrected Dall-Kirkham|
|Aperture||17 inch (432 mm)|
|Focal Length||2939 mm (115.71 inch)|
|Central Obstruction||23.7% by surface area; 48.6% of the Primary Mirror Diameter|
|Back Focus from Mounting Surface||10.24 inch (260 mm)|
|Back Focus from Racked in Focuser||7.24 inch (184 mm)|
|Weight||106 lbs (48 kg)|
|OTA Length||42 inch (1067 mm)|
|Optical Performance||6.5 micron rms at 21mm and 9.6 micron at 26mm off-axis|
|Upper Cage||Carbon Fibre Truss|
|Lower Cage||Carbon Fibre Truss with Carbon Fibre Light Shroud|
|Optimal Field of View||70mm Image Circle|
|Diameter||190 mm (7.48 inch)|
|Coating||Enhanced Aluminum - 96%|
|Optical Diameter||17 inch (432 mm)|
|Outer Diameter||17.5 inch (445 mm)|
|Material||Precision Annealed Borosilicate or Fused Silica|
|Coating||Enhanced Aluminum - 96%|
|Diameter||105 mm (4.13 inch)|
|Number of lenses||2|
|Coating||Broadband AR Coatings (less than .5% reflected from 400 to 700nm)|
|Carbon Fiber Truss Design||Minimizes thermal expansion which causes focus shift with changes in temperature|
|Dovetail Expansion Joint||Allows for the difference in thermal expansion between carbon fiber and aluminum. The expansion joint allows the aluminum dovetail expand and contract without stressing the carbon fiber lower truss|
|Cooling Fans||Three cooling fans ejecting air from the back of the telescope and four fans blowing across the boundary layer of the mirror surface. This helps the telescope to reach thermal equilibrium quickly. The fans are controlled by a computer if the optional Electronic Focus Accessory (EFA Kit) is purchased.|
|Type||Alt-Azimuth / Equatorial Direct Drive Mount|
|Weight||257 lbs (100 kg)|
|Component Weights||AZ base: 55kg (121lbs) ; Fork arm 62kg (136lbs)|
|Max. Load Capacity||200 lbs (91 kg)|
|Latitude Range||0 to 90 degrees, Northern and Southern hemispheres|
|Cable Management||Equipment cables can be wired through mount|
|Control Electronics||PlaneWave Interface dual axis telescope control|
|User Interface||PlaneWave Interface 4 (PWI4) Control Software with integrated PointXP mount modeling software|
|Homing Sensors||Home position sensors are included allowing the mount can find its home position on power up.|
|Slew Rate||20 degrees per second (standard); 50 degrees per second (maximum), both axes|
|Power Requirement||Accepts 120 VAC. Supplied with 12VDC 15A Regulated Power Adapter|
|Motor Control||Industrial grade brushless motor control system and built in electronics|
|Motor - Azimuth and Altitude||Direct Drive 3 Phase Axial-Flux Torque Motors|
|Encoder - Azimuth and Altitude||152mm disk built into the azimuth and altitude axes with stainless steel encoder on the circumference with reader yields 18,880,000 counts per revolution of the telescope. This translates to about 0.069 arcsecond resolution|
|Motor Torque||Approximately 20 ft-lbs continuous; 50 ft-lbs peak|
|Drive Electronics||Industrial grade, off-the-shelf brushless motor drives for each axis with custom designed interface card|
|Telescope Control Software||PlaneWave Interface (PWI4). 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||< .3 arcsecond error over 5 minute period|
|System Natural Frequency||10 Hz or greater|