Technical Guide: Telecentric Illuminations

Collimated backlight illumination improves the edge detection in optical metrology and results in a higher measurement precision. This is especially true if collimated illumination is combined with telecentric lenses which reduces reflections and light scattering from object edges.

The terms “collimated illumination”, “telecentric illumination” or “condenser lighting” are used as synonyms. An appropriate suitable lens images a light source (normally an LED) to infinity to obtain a parallel optical beam path.

The standard selection contains 3 options which differ in electronic control, lighting modes (steady light, pulsed light, flashed light), type of electrical connection and illumination level. The following descriptions and tables list the equivalent sizes and colors.

We offer our optical subassemblies with different LED colors (R, G, B, IR).

The optical design is optimized for narrowband wavelength range ± 50 nm so that there is no resulting color fringing and no blur at the object edges. A broadband correction for applications with white illumination is only given for condensers with a diameter of Ø 55 mm (S6LTC200x and S6IRI148x). However the combination of white light sources and other condenser sizes is also practicable with sufficient performance in many cases.

The spectral range for narrowband illumination is between 400 nm to 900 nm.

Perfectly collimated/telecentric LED condensers would be possible with a point light source with an ideal radial beam characteristic. This kind of light source does not exist in reality. The smaller illuminations (up to clear aperture Ø 73 mm) are able to reach a telecentricity error of about clear aperture of 0.2°. The telecentricity error is about 0.5° for middle sizes (clear aperture Ø 90-150 mm) and about 1-2° for large condensers (clear aperture Ø 150 mm and larger).

A perfectly collimated light beam would have a constant size which does not depend on the distance between the condenser and the illuminated object. In practice a recommended working distance is required to maintain lighting homogeneity. It has to be taken into account that the illuminance decreases with the distance.

The recommended working distance can vary depending on the application, the light output requirement and required homogeneity.

Condensers are a coherent illumination system with LED light sources which fall under photo biological safety regulation DIN EN 62471. It must be pointed out that the critical values for photochemical and thermal retina damage are indicated for long term exposure.

It must be suggested that the capacity of collimated lighting is higher inside the beam path whereas there is no stress outside. The following is recommended when using coherent illumination classified in risk group 3:

1. A suitable eye protection must be worn during the installation and adjustment.
2. Mechanical barriers should be used to prohibit a direct eye contact within the beam path.
3. Applicators and users, working in the direct environment, must be instructed about the safety precaution on an annual basis.

The latest series of telecentric lighting is characterized by a very high homogeneity distribution even for large working distances and a higher maximum power. Furthermore this series is the only one with an integrated potentiometer.

- Integrated potentiometer for regulating the luminous intensity (10 - 100%), manually with a screwdriver directly at the condenser
- M8, 4 pin connection (+24 V; GND; trigger; trigger GND) - Voltage 12 – 24 V, dimmer for current limiting, maximum 4.4 W
- Pulsed operation by trigger input (5 – 24 V), maximum 25 kHz, no “flashing” possible
- Accessories:
      o S6MEC1480/LTC: Voltage 12 V with M8/4 pin with cable set (2 m) included
      o S5ZUB0006/xxx: cable set 2 m with M8/4 pin socket for open cable end

The second generation of telecentric lighting provides a high power LED, which can be connected to the power supply. Because of its LED features it can be dimmed, switched and flashed.

- M8, 3 pin connection (+350 mA; GND) or for open cable end for PG7 cable gland (cable length 300 mm)
- Direct LED connection, max current 350 mA
- Flashing up to max. 500 mA possible
- Accessory:
     o S5ZUB0001/350: current limiter 350 mA with power pack and cable set (2 m) included
     o S6MEC2323/350: analog dimmer with power pack and cable set (2 m)
     o S6MEC2326/350: digital dimmer with power pack and cable set (2 m)
     o The accessory is compatible to the M8/3 pin executions (combine always with S6IRIxxxx/211)

This series is the first generation of telecentric lenses and works well for low power applications. For a voltage of 12 – 24 V an internal circuit limits the current. Below this voltage the intensity can be dimmed by regulating the voltage. The IR condenser has similar electronic features to the Correctal TC high power series. Although it is a part of the standard series because of its output power.

- M8, 3 pin connection (+12 – 24 V; GND) or open cable end for PG7 cable gland (cable length 300 mm)
- Integrated current limiter for a maximum current of 20 mA, not flashable
- Accessories:
       o S5MEC1480/211: Voltage 12 V with M8/3 pin, cable set (2 m) included
       o S5ZUB0007/xxx: cable set 2 m with M8/4 pin socket for open cable end
       o The accessory is compatible with M8/3 pin executions (combine always with S6IRIxxxx/211)

- M8, 3 pin connection (+100 mA; GND) or open cable end for PG7 cable gland (cable length 300 mm)
- Direct LED connection, maximum current 100 mA
- Flash up to maximum 2500 mA possible
- Accessories:
      o S5ZUB0001/100: current limiter 100 mA with power pack and cable set (2 m) included
      o S6MEC2323/100: analog dimmer with power pack and cable set (2 m)
      o S6MEC2326/100: digital dimmer with power pack and cable set (2 m)
      o The accessory is compatible with M8/3 pin executions (combine always with S6IRIxxxx/211)

Our condensers are available with different modifications, such as a glued mechanics or an integrated diffusor.

Customized setups or interfaces for customer specific light sources can also be offered upon request.