Results with Machine Vision Filters
Comparison to Photographic Filters
Comparison to Narrow Band Filters
Recommended Filters for Machine Vision
Kits for testing Filters and Lighting

What is the difference between a machine vision filter and a narrow band filter?

Tolerance Shift
Each LED lamp has a nominal peak wavelength at which it is intended to operate. Due to manufacturing tolerances, however, that peak can vary +/- 10nm and
20-30nm on the tail ends of the output curve. A narrow bandpass filter will not cover all of that tolerance shift and will block some, if not most, of the light's output.

The MidOpt broad bandpass filter will easily accommodate a normal tolerance shift in either direction.

Blue Shift
When a subject is viewed at an angle to a filter, the reflected light travels a path through the filter that is significantly longer (say, 1.4x) than if it's straight-in. Each layer of coating is then optically thicker which
creates a phenomenon known as "blue shifting." At 45º, this equates to a shift of about 30nm; a 20nm bandpass filter doesn't have enough width to allow for that shift. Therefore, the scene gets darker, often much darker
as it moves toward the edge of the frame.

MidOpt filters are broad enough that the blue shift effect won't be noticed.

Manufacturing Differences
A 20nm narrow band filter is made using multiple substrates and many layers of soft coating sandwich sealed with epoxy, creating a thick filter in a thick, often unthreaded, metal mount. The thickness also affects peak transmission – up to about 80%. The life span of this type of filter is usually 5 years, less if in hot, humid conditions or if mis-handled. Initial failures may not be evident to the eye but performance will change noticeable over time.

MidOpt filters exceed 90% transmission and feature a unique "hard coating" for a nearly unlimited life span.

Finally, the lesser amount of light from today's LEDs, combined with lesser transmission through a narrow band filter, modified by any of the above conditions,
will greatly darken the overall view of the subject.
This can make aiming the camera and staying oriented difficult, particularly with the lights turned off.

Filter comparisons:

Figure 1. LED tolerance shift illustration shows MidOpt broad bandpass filter accommodating the entire light source regardless of the shift.

Figure 2. Narrow bandpass filters do not accommodate the blue shift.