This directory contains information for Mosaic, 4x4-inch, 2x2-inch KPNO filters and filters used at the WIYN Observatory.. 1x1-inch filters are no longer supported. All measurements have been done with the NOAO Perkin-Elmer Lambda 9 Spectrophotometer with an ~f/13 beam. For further information contact: Jim De Veny (deveny@noao.edu) or Bill Schoening (schoen@noao.edu).

Filters are generally not available for loan to non-NOAO organizations. The policy is listed in NOAO Newsletter #41, March 1995, pg. 59.

The General 4-inch and 2-inch filter lists tabulate all the available filters by size (sorted by wavelength). These are the preferred lists for browsing. USERS SHOULD BE AWARE THAT ALL THE OLDER (LATE 1970'S TO 1980'S) 2X2-INCH AND 4X4-INCH FILTERS CAN HAVE SIGNIFICANT RED LEAKS. Examine the data closely before using one of these filters or request that the filter be rescanned. Unless noted otherwise, all data is for an f/13 beam.

The various data/plot directories contain digital transmission data and PS files of plots.

• 2indata Data for 2-inch filters
• 4indata/plots Data and plots for 4-inch filters
• Irdata/plots Data and plots for IRIM filters
• Wiyndata/plots Data and plots for WIYN Imager filters
• Rcspecplots Plots of RC Spectrograph order separation filters
• Gcamplots Plots of order separators for GoldCam spectrometer
• HBfs Data and plots for the 4x4-inch Hale-Bopp comet filter set

The best filters of the 2-inch H-Alpha set A and set B have been combined into one set. Due to age and deteriorating condition, the filters were combined into a single set. SINCE MANY OF THESE FILTERS ARE SUB-STANDARD, OBSERVERS SHOULD EXAMINE THEM BEFORE USE. Some of these filters also have a clear edge that requires masking to eliminate light leaks.

Each filter of the combined set was rescanned on 7/23/96 and is updated in 2inchdata directory. These filters are listed as ha*.

KPNO has 2 and 4 inch Polarizers. The "4-inch" are Tiffen 77mm diameter SR polarizers purchased at a local photo shop. The set consists of four 4x4-inch adapters containing the 77mm round polarizers. Each must be calibrated/rotated for angle of polarization. This set resides in the Instrument Prep Room at the 4-Meter Telescope.

The 2-inch set manufacturer is unknown.

Digital transmission data for both sets may be examined in the 2indata and 4indata directories. Pol*in files are scans of one polarizer. Pol*in90 files are two polarizers oriented 90 degrees apart.

• Central wavelength (CWL) shifts with focal ratio:

The CWLs in the lists are measured with the KPNO Lambda-9 spectrometer that works at ~f/13. When using these filters at other focal ratios, the following shifts are typical:

4m Prime Focus (f/2.8) -13 to -21 Angstroms

Burrell Schmidt (f/3.5) -9 to -13 A

f/7.5 Telescopes(2.1m and 0.9m) -2 to -3 A

• Temperature/CWL shifts:

There also will be a shift to the BLUE if the temperature of the observing environment is COOLER than the temperature at the vendor's lab where the filter was made. Similarly, a shift occurs due to the temperature difference between our lab and the dome. A typical shift is 1A to the BLUE for every 10 degrees Fahrenheit of COOLING (5.5 degrees C.). Thus, if we measure the filter in our 74 degree F lab, when used at 44F degrees on Kitt Peak, there will be a 3A blue shift of the filter curve.

• Observers should be aware of the folly of trying to use very narrow filters in fast beams. A good rule of thumb for ~f/3 beams is to maintain a minimum FWHM of ~30A.

• Narrower filters will broaden back to about 30A FWHM, while the peak transmission drops significantly when placed in fast converging beams.

G. Jacoby, and J. De Veny

Updated: 9/24/99