Stray light – what is it, and what kinds of stray light exist?
What is stray light? Stray light is light which enters a system from outside the field of view and therefore is reflected from internal part surfaces of the system and eventually reaches the detector impacting signal to noise or image quality as the case may be. This is prevented by a combination of mechanical design and low reflectivity coatings. Acktar black light absorbing coatings are the premium coating used in these applications.
Types of Stray Light
Stray light is separated into two categories, ghosts or flare and veiling glare. Ghost stray light is when a photo is being taken and the light undergoes unwanted reflection which causes it to create a ‘ghost image’ in the picture. An example would be a secondary image of bright surfaces appearing in a photo. Flare and veiling glare typically occur when light scatters within the optical system being the spectrophotometric detector. An example of this would be if a picture is being taken of a candle the picture of the object will come out hazy or foggy because of the thermal radiation coming from warm surfaces.
Monitoring Stray Light
Stray light is important to monitor to produce the best quality images possible. Stray light may alter the contrast of an image if not caught before. For detection systems, stray light could reduce sensitivity of the photo. Stray light could also make unwanted blind spots appear. For ghost images there is a ray sequencing software that can be used to analyze an image that might catch stray light before it happens. This software is in a form of a filter that absorb such light at the wavelength which is then captured and does not appear in images. A monochromator is a tool used within a spectrophotometric detector which also is another way to search for stray light. Flare light can appear more unexpected compared to ghost light. This because there are so many different paths flare light may appear that it is harder for a monochromator to catch the light.