Industry News
IR Shift Problem
  Date:2010-5-14   Browse: 1429

The issue of night-time performance is important to integrators as they make more use of IR illumination.  But such illumination brings with it the complication of IR shift, the difference in focal points for a lens under white and IR lighting. 

Rainbow is an acknowledged leader in the manufacture of day-night lenses which correct this shift, making both visible and IR rays focus on the same point and so eliminating the need for adjustment. 

It is Rainbow’s experience that operators and end users are never slow to tell integrators and manufacturers that the more they zoom in on an object the more IR shift becomes noticeable.

Locations requiring continuous day and night observation of objects that are 50 feet or more away are particularly fraught since the greater the zoom factor the more depth of focus goes down.  At night when the iris is generally sitting wide open you are already at your worst depth of focus.

This is why IR shift becomes more pronounced and why Rainbow impresses on customers that it is critical to invest in high quality day-night lenses for applications using IR illumination.  If the application requires observation 24 hours a day and relies on IR rather than street lighting or floodlights, then a day-night lens becomes a must.

In the past clients were often asked to specify whether day or night-time images were more important and were then expected to settle for an unfocused image for part of the day. Few will accept this now.

Of course focus shift is not so important in a motorised zoom that is manned all the time since the operator can simply refocus.  But with the popularity of remote observation and automated intelligent scene analysis such usage is becoming rare.  Similarly, an application that uses pre-sets will normally need a day-night lens since images during IR illumination employing a pre-set chosen in daylight are bound to be blurred.

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