A method reduces drift induced by environment changes when imaging radiation from a scene in two wavelength bands. Scene radiation is focused by two wedge-shaped components through a lens onto a detector that includes three separate regions. The wedge-shaped components are positioned at a fixed distance from the lens. The radiation from the scene is imaged separately onto two of the detector regions through an f-number of less than approximately 1.5 to produce a first pixel signal. Imaged radiation on each of the two regions includes radiation in one respective wavelength band. Radiation from a radiation source is projected by at least one of the wedge-shaped components through the lens onto a third detector region to produce a second pixel signal. The first pixel signal is modified based on a predetermined function that defines a relationship between second pixel signal changes and first pixel signal changes induced by environment changes.