.. index:: In field area; proportional
   
Proportional In Field Area
==========================

The simplest way of defining the In Field Area (IFA) is as a proportion of the field size as defined by the FWHM. The default is 80% of the FWHM. This corresponds to most definitions for standard fields such as 10x10 and 20x20, but may overestimate the in field area for small fields (< 5cm) and underestimate the in field area for large fields (> 30cm).

To set a proportional IFA under "Settings" select the "IFA Type" as "Proportional" and the "IFA Factor" as a proportion where 1.0 will include the entire field and 0 will include nothing.

|Note| For offset fields the proportional IFA will also be offset.

.. |Note| image:: _static/Note.png