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Central Wavelength Shift Calculator
Text:
Central Wavelength Shift Calculator
This tool can be used to calculate the shift of the central
wavelength passed by a filter, when at least some of the light is incident
at an angle to the normal.
The shift is calculated for one of the following: converging beam
incident on filter; ray of light (or collimated beam)
incident at a specific angle to the normal; convering beam incident at an
angle to the normal. Ambient temperature can also be considered.
ACAM allows filters mounted in either the focal plane or the pupil plane, which has different implications for the transmitted values of the filter central wavelengths. See narrow-band imaging with ACAM for more information.
Focal station
Field of view (arcmin)
ACAM (WHT Cass.)
PFIP (WHT Prime)
PAUCam (WHT Prime)
WFC (INT Prime)
8.3
16
60
34
Reference values
Focal station
Plane
Beam
Distance from center (arcmin)
Focal ratio (F)
Angle of incidence* (°)
INT Prime
Focal
Converging
0
3.29
0.00
INT Prime
Focal
Converging
17
3.34
1.72
WHT Cassegrain
Focal
Converging
0
10.95
0.00
WHT Cassegrain
Focal
Converging
4
10.95
0.24
WHT Cassegrain
Pupil
Collimated
0
10.95
0.00
WHT Cassegrain
Pupil
Collimated
4
10.95
7.72
WHT Prime
Focal
Converging
0
2.81
0.00
WHT Prime
Focal
Converging
20
2.90
2.99
WHT Prime
Focal
Converging
30
3.05
4.91
Filter
Angle of incidence (AoI, incident angle to the normal, maximum 10°): ° (leave blank for a range of wavelength shifts and AoI).
1. Nominal central wavelength (or wavelength of peak transmission): Å
Provide a value for a collimated beam, i.e. not for a particular F ratio
2. Refractive index:
Effective refractive index of the total filter (glass + coating), generally varying from 1.6 to 2.6 (n=2.1 is an average)
3. Temperature.
Nominal temperature at which central wavelength of the filter is specified:
°
Temperature coefficient at nominal central wavelength:
Å/°C
(typical values are 0.15Å/°C at 4000Å or 0.20Å/°C at 8000Å)
Ambient temperature:
°
(T=9° is a typical average)
