PlaneWave IRDK 20" DAll-Kirkham
This is a Dall-Kirkham optical design with coatings that are optimized to transmit in infrared or ultra violet wavelengths. It is diffraction limited across a 20mm image circle at the focal plane. There are no refractive lens, only reflective components to the design. For IR application, reflectives coatings are a protected gold which give better than 98% reflectivity from .65 micron (650nm) to 5 micron (5000nm). This design is ideal for infrared astronomy or LIDAR applications. UV optimized coatings can also be used at an additional cost.
The DK is available in the three different apertures 12.5 ", 20", 24" and 28".
The PlaneWave IRDK 20 is available in various types of mirror material. Standard mirror material is borosilicate. The telescope is also available in fused silica optics (Verlinkungen zu den einzelnen Ausführungen)
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.
Aperture 20 inch (508 mm) Focal Length 3454 mm(135.98 inch) Focal ratio f/6.8 Central Obstruction 39% of the Primary Mirror Diameter Back Focus from focuser Mounting Surface 8.9inch (226 mm) Back Focus from Racked in Focuser 5.81 inch (147 mm) Weight 140 lbs (63.5 kg) OTA Length 47 inch (1,194 mm) UpperCage Carbon Fiber Truss Lower Cage Carbon Fiber Truss with Carbon Fiber Light Shroud
Optical Diameter 20 inch (508 mm) Outer Diameter 20.5 inch (521 mm) Shape Prolate Ellipsoid Material Precision Annealed Pyrex Coating Protected Gold Reflective Coating - 98% (.65-16micron)
Diameter 7.5 inch (191mm) Material Precision Annealed Pyrex Shape Spherical Coating Protected Gold Reflective Coating - 98% (.65-16micron)
Carbon Fiber Tube 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 blow air inside the back of the telescope. 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.
|Back Focus Distance||8.9" (226 mm) from Mounting Surface, 5.81" (147 mm) from Racked in Focuser|
|Aperture (mm)||20" (508 mm)|
|Focal Length||3.454 mm (135.98 inch)|
|Image Field||52 mm|
|Central Obstruction||39% of the Primary Mirror Diameter|
|Optical tube length||47 inch (1.194 mm)|
|Optical Tube Weight Copy||140 lbs (64 kg)|