Fundación Galileo Galilei - INAF Telescopio Nazionale Galileo 28°45'14.4N 17°53'20.6W 2387.2m A.S.L.

SARG - Filters set

SARG filters are listed in the following Table. In the table is also indicated the different position on the correspondent filter holder. PS= Preslit Slide; FW= Filter Wheel; FF= Flat Field lamp.

Pos. Name Recipe Application
Neutral Filters
PS3 ND 0.5 NG4 Flux Calib.
PS4 ND 2.0 NG9 (1.40) Flux Calib.
PS5 ND 3.0 NG9 (2.83) Flux Calib.
Stray light rejection and Order Sorting Filters
FW2 FW2 BG40 (1.0) Stray light rejection
FW3 FW3 KG4 (2.0) Stray light rejection
FW4 FW4 GG455 (2.0) Order Sorting
FW5 FW5 OG570 (1.0) Order Sorting
Light Balance Filters
FF1 FF1 UG5 (1.2) + NG9 (0.3) Flats Balance
FF2 FF2 BG24 (1.0) + BG40 (1.5) + UG3 (1.0) Flats Balance
FF3 FF3 BG26 (3.0) Flats Balance

All filters do not affect focus since they are in parallel beam. Image maximum shift on the slit when inserting a filter corresponds to about 0.3 arcsec for a thickness of 3mm. All filters are tilted by 3 degrees to avoid ghosts.

Neutral filters

SARG Neutral filters set

The neutral density filters are placed in the Preslit slide (5 positions available). Normal operation of SARG is with Preslit Slide in position PS1. Filter dimensions are f 12.7 × 2 mm. Mechanical dimensions of cell is f 20 × 14 mm. Cell mounted in wheel at tilts of 3 degree.

Light rejection filters

SARG light rejection and order sortening filters set

The order sorting and background suppression filters, as well as custom interference filters, are placed in the Filter Wheel (12 positions reserved). Normal operation of SARG is with Filter Wheel in position FW1. Filter dimensions are f 12:7 × 2 mm.Mechanical dimensions of cell is f20 × 14 mm. Cell are mounted in the wheel at tilts of 3 degree.

Light balance filters

SARG  light balance filters set

Each Flat Field calibration lamp is equipped with colored light balance filters in order to reduce range in intensity due to the poor output of the lamps in the UV. Each lamp, with its color filter, is intended to be used in a limited wavelength region with one particular cross disperser. The flat balance filters are mounted in front of the respective lamps.

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