1.2m CCD Filters

Observers are not allowed to change CCD filters. Please ask the staff by phone or email and the 1.5m observers (check the observing schedule) by phone or email well before you arrive if you need to change filters. Plan to arrive the day before your run, especially if you will be bringing filters.

We have 3 sets of 4" optical filters currently in use:

The Harris set featuring BVRI (labeled with the name plus an H in fits headers, e.g., BH) was delivered in fall 1998. These filters are thinner than the SAO set, and are MgF coated. We also have a U filter with a liquid CuS04 cell for red blocking, far superior to the all-glass U filter of the old SAO set. The filter broke during a very cold night in Jan 2007. We ordered a new one from Custom Scientific. It arrived on 6 June 2007. We filled the cell with CuSO4 on 8 June and mounted the new filter. Click here for transmission curves or for a listing . We have no curve for the U filter with CuSO4, but here is the transmission curve that Custom Scientific delivered with the new filter (the red "leak" is taken care of by the CuSO4).
NOTE that at the end of November 2007, we discovered the cell was leaking CuSO4. We could not determine the location of the leak, but we suspected one of the seams. We sent the filter to Custom Scientific on 11/29/07 for diagnostics and repair. The filter was repaired at no cost and returned. We tested it and found no leaks. We re-installed it on 02/04/08.
NOTE that on 01/24/09, Perry Berlind discovered the U filter had leaked CuSO4 again. This time it was a catastrophic failure: the glass cracked as can be seen here. We traced the problem back to an extreme cold event at the end of December 2008. We intend to replace the filter, this time avoiding liquids. One possibility is Bessel U. The timescale is unknown as of January 2010. Contact the staff if you will need a U filter.

The interference I filter was delivered in April of 1999. It has a better-defined transmission curve than the SAO I, which is a long pass filter, thus even though the improvement is small (10%), the transformation to standard Kron-Cousins I should be better than for data taken with the SAO I filter.

The Harris BVRI filters are parfocal, but for U, the focus is about 115 (old) units higher. You can set this value from the telshell window thus:
tele focus -115
or you can enter the value using the hexapod native mm:
tele hfocus -0.146
or you can move the focus to this value using the TCS GUI under menu item "Focus Move." If you are not using scripts to observe, you will need to remember to manually undo the focus move above for filters other than U.

The SDSS (Sloan) set featuring ugriz. Here are the transmission curves and listings. The curve for the g filter is incomplete. The previous i filter was badly cracked; it has been replaced with an Omega 767.2wb153.5 i.

As of July 2010, all of these filters showed a marked deterioration, z being worst. We ordered a new, full set of SDSS filters from Custom Scientific; delivery was first scheduled for October 2010. Due to some delays in production, we received the filters in early March 2011.

We mounted the new filters in their holders, and on the filter wheel on 04/06/11. The new filters are of excellent quality; they have higher throughput than the old ones. The following table shows statistics for new/old ratios of bias-corrected and imcombined dome flats through the new (old) griz filters taken on 04/06/11 (04/03/11), using the same exposure time for each filter on both dates; for u band we used sky flats through the new (old) filters, taken on 04/08/11 (03/29/11) and scaled by their average exposure times:

#          IMAGE     MIDPT      MEAN    STDDEV
    NewOldg[IM1]     1.086     1.084   0.01034
    NewOldg[IM2]     1.085     1.086   0.01029
    NewOldg[IM3]     1.093     1.092   0.01458
    NewOldg[IM4]     1.091     1.089   0.01309
#          IMAGE     MIDPT      MEAN    STDDEV
    NewOldr[IM1]     1.175     1.177  0.009063
    NewOldr[IM2]     1.189     1.188   0.01486
    NewOldr[IM3]     1.206     1.207   0.02012
    NewOldr[IM4]     1.209     1.209   0.01833
#          IMAGE     MIDPT      MEAN    STDDEV
    NewOldi[IM1]     1.075     1.076   0.01196
    NewOldi[IM2]     1.063     1.064  0.007402
    NewOldi[IM3]      1.06     1.061  0.003342
    NewOldi[IM4]     1.062     1.063   0.00575
#          IMAGE     MIDPT      MEAN    STDDEV
    NewOldz[IM1]     1.022     1.022  0.004637
    NewOldz[IM2]     1.014     1.014  0.003234
    NewOldz[IM3]     1.021     1.022  0.005751
    NewOldz[IM4]     1.013     1.013  0.002757
#          IMAGE     MIDPT      MEAN    STDDEV
    NewOldu[IM1]     1.055     1.055   0.01118
    NewOldu[IM2]     1.044     1.044   0.01133
    NewOldu[IM3]     1.046     1.051   0.01501
    NewOldu[IM4]     1.055     1.054   0.01194

Here are the transmission curves for the NEW Sloan filters, shown together with the old filters and listings.

The narrow-band set of filters featuring:

[OII]3727 curve and listing
[Ne III]3869 curve and listing*
[OIII]4363 curve and listing
He II 4686 curve and listing
[OIII]5007 curve and listing*
G continuum curve (5260) and listing
H_alpha_6563 (5nm FWHM) curve and listing
H_alpha_6563 (1nm FWHM) curve and listing*
SII 6725 (5nm FWHM) curve and listing
R Continuum (7130) curve and listing

Note: asterisks indicate filters that may require mounting in holders; request these well in advance of your run.

Click here for a description of older filter sets in their dotage.

Created 10/12/99 by NC
Updated: 08/18/10 by EF