The filter lists have been divided into three sections:

1) narrow- and medium-band filters kept at the 3-meter telescope,
2) broad-band and neutral density filters kept at the 3-meter, and
3) filters kept at the 1-meter.

The values given are generally those provided by the manufacturer. In many instances passbands are available for the filters, but they are from many sources and were determined in many ways by many people, so we do not include them here.

Most of the filters are 2" square, perhaps 10% are 2" round, and a few are 1" round. We have a few extra filter holders available at the telescopes for user filters.

The filter lists may be incomplete in two ways; first, filters may have been missed in the initial listing or added since the lists were compiled, and second, a few filters on hand are unidentified.

The lists do not include filters which are normally mounted within an instrument, and are therefore not available for borrowing. See the appropriate instrument manual for the normal filter complement at a particular instrument.


Traces for many of the interference filters can be found in a binder kept with the filters in the 3-meter.

Traces and transmission tables for most of the broadband filters are given in Optical Glass Filters, from Schott, Inc., a copy of which is kept at the filter collection at the 3-meter.

Traces and transmission tables for B, V, R, I, and Rs are available online in tabular form.


Few of these filters are owned by Lick Observatory. The majority belong to individual astronomers within the UC system who generously make them available to the rest of us. Please treat them with care.

Most of the filters are stored in the 3-meter; a few are at the 1-meter. The former are kept in drawers in room 286, off the 3-meter observing floor to the east. Two drawers contain narrow- and medium-band interference filters, filed by central wavelength. A third drawer holds broad-band and neutral density filters. When borrowing filters, please complete a checkout slip for each, and place the slips in the slots from which the filters were removed. Be sure to include the telescope and instrument to which you are taking them.
Please return filters promptly!

Priorities for the use of filters are owner, 3-meter observer, and then others. If you wish to use a particular filter at another telescope, please verify first that it will not be needed at the 3-meter.

Do not attempt to clean filters yourself. Many have soft coatings!!!
Please notify a staff member if a filter needs cleaning.


Observers who add filters to the collection are urged to mark them clearly and in a permanent way. Commercial interference filters are usually adequately marked, although some manufacturers use obtuse (and even unintelligible) codes. Plain glass filters are the ones which we most commonly find completely unmarked. A good technique for marking such (relatively inexpensive glass) filters is to scratch their identity unobtrusively near the edge of the filter with a diamond tipped stylus. Interference filters and filter sandwiches are usually thick enough to write a description on the side. Remember to notify a support astronomer if you've added a filter so that we can include it in the list.