Ray optics is based on the assumption that light travels in a straight line. Diffractions observed when light propagates through small apertures/slits or around small objects disproves this assumption. Yet the ray optics assumption is so commonly used in understanding location and several other properties of images in optical instruments. What is the justification?

Explanation

The apertures of optical instruments are much larger than the wavelength of the light passing through them. So there is no possibility of any diffraction to take place and there is no anomaly in the wave optics and ray optics in all practical purposes.