Filters

Photometric filters in Synthesizer are defined using two dedicated objects:

  • A Filter object: individual filters defining a filters wavelength coverage and transmission, with related methods and attributes.

  • A FilterCollection object: a collection of Filters that behaves like a list and a dictionary, with extra attributes and methods to efficiently work with multiple Filter objects.

We provide a number of different ways to define a Filter or set of Filters:

  • Generic: A generic filter simply requires a user defined wavelength array and transmission curve to initialise. A user can then define any arbitrary filter they like using this functionality.

  • Top Hat: A top hat filter’s transmission is 1 in a particular range and 0 everywhere else. These are either defined by a minimum and maximum wavelength of transmission, or by the effective wavelength of the transmission and its full width half maximum (FWHM).

  • SVO: We also provide an interface to the Spanish Virtual Observatory (SVO) filter service.

    The user need only provide the filter code in “Observatory/Instrument.code” format (as shown on the SVO website) to extract the relevant information from this service, and create a Filter object.

Filters can be used for producing photometry from Sed objects, as well as for creating monochromatic or RGB images. In practice they are most commonly attached to PhotometricInstrument or PhotometricImager objects for use with observable generator methods.