Celestron CG-4 Bedienungsanleitung PDF herunterladen (Seite 8)

GENERAL INFORMATION

1.2.1 Properties of the Silicon window

CG 4 uses a specially designed pure silicon window. Although the

window isn’t hemispherical, CG 4 has a 180° field of view with good

cosine response.

A big advantage of the meniscus shaped window over the typical

spherical window is the ability of the coating manufacturer to deposit a

more uniform coating on the window surface. Deposition of a uniform

filter coating on a strongly curved surface is a rather difficult, possibly

impossible process.

With that knowledge Kipp & Zonen developed a window with a good

optical quality due to an optimal shape and coating uniformity.

In this way a CG 4 window allows equal dome transmittance over the

whole window surface.

The diamond-like coating also called “ Hardcarbon coating “ is a

carbon layer of a few microns thickness, with the main purpose of

providing optimal protection against environmental influences.

An additional advantage is that the hardcarbon acts as an

anti-reflection coating, which leads to a transmittance increase.

The solar blind filter is opaque for radiation under the 4.5 µm known

as the cut-on wavelength. The low-pass filter deposited at the inside of

the window is an interference filter. Currently most pyrgeometers have

their cut-on at a lower wavelength. Problems may occur in case of

clear sunny days with low humidity. In the solar spectrum between 2.5

and 4.5 µm, there can be still an amount of infrared solar radiation up

to 10 W/m

. This unwanted fraction would increase the amount of

downward radiation unavoidable. In the CG 4 this signal is blocked by

the filter coating.

The CG 4 window transmittance curve is given in figure 1.2

The transmittance is given at normal incidence.

1 2 3 4 5 6 7 8 9 10 11 12 13 ... 63 64

Keine Kommentare

Celestron CG-4 Bedienungsanleitung Seite 8