About the iris

Why Opto Engineering® telecentric lenses do not integrate an iris?

Our TC lenses don’t feature an iris, but we can easily adjust the aperture upon request prior to shipping the lens, without any additional costs or delays for the customer. The reasons why our lenses don’t feature an iris are so many that the proper question would be why other manufacturers do integrate irises?

• adding an iris makes a lens more expensive because of a feature that would only be used once or twice throughout the product life
• iris insertion makes the mechanics less precise and the optical alignment much worse
• we would be unable to test the lenses at the same aperture that the customer would be using
• iris position is much less precise than a metal sheet aperture: this strongly affects telecentricity
• the iris geometry is polygonal, not circular: this changes the inclination of the main rays across the FOV, thus affecting the lens distortion and resolution
• irises cannot be as well centered as fixed, round, diaphragms: proper centering is essential to ensure a good telecentricity of the lens
• only a circular, fixed, aperture makes brightness the same for all lenses
• an adjustable iris is typically not flat and this causes uncertainty in the stop position, which is crucial when using telecentric lenses!
• iris is a moving part that can be dangerous in most industrial environments. Vibrations could easily disassemble the mechanics or change the lens aperture
• the iris setting can be accidentally changed by the user and that would change the original system configuration
• end-users prefer having fewer options and only a few things that have to be tuned in a MV system
• apertures smaller than what is delivered by OE as a standard will not make sense as the resolution will decay because of diffraction limit; on the other hand, much wider apertures would cause a reduction of the field depth.
• the standard aperture of OE lenses is meant to optimize image resolution and field depth.