Specifications

Background
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tuning error is consistent with the one measured prior to the test. One of the main issues
connected to the use of this kind of filter is the need of custom-designed optics instead of
a commercial one; this is due to the filter causing a variation of the B.F.L. (Back Focal
Length) which, in turn, results in a shift of the focus of the system. The filter has an
aperture of 35 mm, thus matching the dimensions of the CCD (main diagonal of 34.76
mm) and the wavelength can be varied between 400 and 720 nm (in the visible spectrum)
with steps of 20 nm.
The number of bands and the value of the acquired wavelengths can be selected (both
after launch, and during the whole mission lifetime) by storing appropriate palette
onboard. This allows a flexible use of the instrument and enables a rapid response on
specific targets, especially during disaster monitoring or for environmental and
agricultural purposes.
Figure 3: Acquisition method, e.g 6 bands image
Diffractive optics have been designed (starting from a telephoto layout with a ratio of
0.9) in order to correct the 6 cm shift of the focal plane due to the filter housing, with a
fixed focal length of 200 mm; five lenses are divided into two main groups and then
inserted in a titanium case which will provide the necessary stiffness during the launch
phase, and avoid misalignments between each lens.
Figure 4: E.F.L = 200 mm, Telephoto Ratio = 0.9, Overall Length = 180 mm, F/# = 4, B.F.L = 60 mm