Filters

The ING owns a large collection of broad and narrow band filters for use in a variety of instruments. The 'database search' tool can be used to list the filters and their key properties (e.g. physical dimension, throughput, central wavelength and FWHM). Information on filters decommissioned can be found in old records.

Dimensions

The following table summarises the different filter sizes in use and the instruments into which they can be inserted. Sometimes a special adapter is required as an instrument has been designed for a larger filter size. For example, many of the TAURUS filters may be fitted into other instruments.

Type	Instruments
Type	Current	Decommissioned
Round 38mm		INGRID
Round 50mm	ACAM	AUX, Taurus^, UES, PFIP^
Square 50mm	ACAM	AUX, JKT imaging, PFIP^*
Round 63mm	ACAM	Taurus^, UES, PFIP^
Round 76mm	ACAM	Taurus^, UES, PFIP^
Round 120mm	ACAM	Taurus^*
Round 125mm	ACAM	Taurus^*, PFIP
Round 139mm	WFC

Notes: (i) A * next to a particular instrument indicates that the filter will give rise to vignetting; (ii) There are two round optical filters of diameter 25mm and 38mm (serial numbers #1 and #2 respectively) which are fitted in 50×50mm holders.

Throughput

The filter throughput data can be accessed by (i) using the 'database search' tool above to list the filters and (ii) clicking on one of the links in the throughput column. Both ASCII tables and graphical representations (png, ps or pdf) are available. The scanner can only measure up to ~9000 Angstroms. Around this wavelength, noise is apparent in the throughput scans. As a result, some I and Z band scans show local throughputs greater than 100%.

Central wavelength

The central wavelength of a filter can be different from the one provided in the database depending on the incident light beam (collimation and incident angle) and temperature. See calculation of central wavelength for more information and use this calculator to quickly compute effective central wavelengths.

Nordic Optical Telescope Filters

In addition to the ING filter set, it may also be possible to borrow filters from the Nordic Optical Telescope (NOT). Some of their filters are complementary to the ING ones (e.g., the NOT has a collection of 51-mm square redshifted Hβ and OIII filters while the ING has a set of 51-mm square redshifted Hα filters). Should you be interested in using one of the NOT filters, please contact the local NOT staff (lstaff@not.iac.es) for permission before proposal submission (note that in all cases priority for the filters will go to NOT users.) At the same time, please email the ING filter contact (below) to check whether the filter can be fitted into the required instrument and whether a special adapter is required.