Science Operations

Filters

There are two filter wheels in each LBC. Each wheel has 5 positions, and since 1 must remain free, at most 8 filters can be available in LBCB and 8 in LBCR at any one time. The filter wheels and the cryostat are all mounted on the derotator, which tracks the sidereal rotation during an exposure. There are 6 filters for LBC Blue and 10 for LBC Red. The TiO784 and CN817 filters are installed in LBC Red only by request. It is important that the partner coordinators and observers communicate the need for these filters to LBTO staff well in advance of the run, to allow scheduling of a filter swap.

The tables below list some of the properties of the filters installed in LBC Blue and Red. Click on the filter name to see the plot of filter transmission and on the “ascii” link for the table. The plots show the curve based on the ascii file (solid black), which for all filters are now the actual measured transmission data.

These transmission data were measured in a collimated beam, normal to the filter surface except for the TiO and CN filters where the beam was at a 5 degree angle of incidence. For interference filters, the transmission in the convergent beam is blueshifted and the FWHM broadened from that measured in a collimated beam. The dashed lines in the transmission plots for the Sloan filters illustrate this effect, where the dashed black lines plot the predicted transmission in a convergent f/1.45 beam. For F972N20, both the transmission as measured in a collimated beam and the modeled transmission in an f/1.45 beam are plotted side-by-side, and for the TiO and CN filters, the calculated shift in the peak is printed on the plots. For Uspec, the shape of the transmission curve depends on where it is measured and three curves are shown, corresponding to points 15mm, 40mm and 60mm from the filter center.

 
If you wish to inquire about the possibility of custom filters, please contact us at sciops-at-lbto-dot-org.
Filters in LBC Blue
Position1 Filter Name 50% cut on [nm] 50% cut off [nm] Peak Trans[%]
11 empty
12 U-BESSEL ascii 333 382 62
13 V-BESSEL ascii 488 610 93
14 SDT_Uspec
ascii_R15
ascii_R40
ascii_R65
15 B-BESSEL ascii 375 469 75
21 empty
22 r-SLOAN4
ascii #1 
552 686 99
23 empty
24 pinhole
25 g-SLOAN
ascii #1 ascii #2
397 550 95

Filters in LBC Red
Position1 Filter Name 50% cut on [nm] 50% cut off [nm] Peak Trans[%]
11 empty
       12  r-SLOAN ascii             553.3             686.6  98.7
13 I-BESSEL ascii 713 881 97
 14  i-SLOAN ascii  697.2  836.9  96.6
 15 z-SLOAN2 ascii  830.0  96.9
 21  empty
22 R-BESSEL ascii 572 690 79
 23  V-BESSEL ascii  493  577  88
 24  F972N20
ascii_meas
ascii_model
 952.5  974.5  81
25 Y ascii 952.5 1110.7 96.6
 TiO 7843 ascii 769  788  97.9
 CN 8173 ascii  802  821  98.3

1. The first digit denotes which wheel, 1 or 2, and the second the position, 1 through 5, in that wheel.
2. The Sloan z’ filter has no red cutoff, it is limited by detector QE which reaches ~0 at 1100nm

3. Only installed upon request.
4. #1 installed, #2 spare.