Previous: Imaging filters
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Previous: Imaging filters
Up: No Title
Previous Page: General Remarks
This is a list of interference filters for use at the WHT, either for narrow-band imaging, or as order-sorting filters for instruments such as TAURUS or UES.
The filters have been scanned using the Guildford Spectrometer at RGO. The measurements covered a region of about 5mm in diameter close to the center of the filters. The measurements were taken with the filters at room temperature. Note that temperature changes will affect the transmission; the central wavelength of an interference filter shifts to the red with increasing temperature, with a temperature coefficient of about 0.2 A/degree C.
The transmission of an interference filter also depends on the angle of incidence of the light on it. This has the advantage that it is possible to fine-tune the central wavelength by tilting the filter; the central wavelength shifts to the blue with increasing tilt angle. For small tilt angles (smaller than 10 degrees) the effective wavelength is given by:
lambda_eff = lambda * ( 1 - (theta)**2/28954 )
It should however be noted that tilting an interference filter also affects the bandpass and the peak transmission; the bandpass increases and the peak transmission decreases with increasing tilt angle. Here is a summary of the filters.
Here are the transmission curves:
3721/28 3737/50 3742/40 3760/34 3769/30 3770/50 4550/100 4550/300 4770/320 4868/15 4880/100 4883/15 4898/15 4912/15 4962/15 4974/15 5000/350 5009/15 5010/100 5012/20 5021/15 5032/20 5033/15 5045/15 5052/20 5065/15 5072/20 5092/20 5108/16 5124/16 5145/15 5164/16 5175/15 5194/16 5216/16 5220/380 5232/16 5247/17 5267/15 5340/15 5700/450 5905/10 5960/490 6240/540 6303/15 6345/18 6565/15 6568/17 6577/15 6589/15 6589/16 6590/130 6601/15 6610/17 6613/15 6631/17 6631/17 6652/17 6667/15 6673/17 6676/15 6689/15 6692/18 6702/17 6714/18 6726/18 6730/50 6741/19 6754/19 6765/18 6770/50 6778/18 6792/18 6803/19 6816/18 6826/17 6838/17 6851/19 6859/16 6872/16 6884/18
And here are the tables with the filters transmissions:
3721/28 3737/50 3742/40 3760/34 3769/30 3770/50 4550/100 4550/300 4770/320 4868/15 4880/100 4883/15 4898/15 4912/15 4962/15 4974/15 5000/350 5009/15 5010/100 5012/20 5021/15 5032/20 5033/15 5045/15 5052/20 5065/15 5072/20 5092/20 5108/16 5124/16 5145/15 5164/16 5175/15 5194/16 5216/16 5220/380 5232/16 5247/17 5267/15 5340/15 5700/450 5905/10 5960/490 6240/540 6303/15 6345/18 6565/15 6568/17 6577/15 6589/15 6589/16 6590/130 6601/15 6610/17 6613/15 6631/17 6631/17 6652/17 6667/15 6673/17 6676/15 6689/15 6692/18 6702/17 6714/18 6726/18 6730/50 6741/19 6754/19 6765/18 6770/50 6778/18 6792/18 6803/19 6816/18 6826/17 6838/17 6851/19 6859/16 6872/16 6884/18