Goldstone Scientific Blog

Getting a small spot at a distance. Collimator or Focuser; which is better?

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Do you need to get intense light delivered at a distance? There are two choices:
1) Collimate the light or 2) Focus the light.

Collimation expands the beam and sends it forward in relatively parallel beams.
A focuser mounts on a collimator and either shrinks or magnifies the spot at a specific working distance.

Which option is best for you?

Short Answer:

  • For a small spot at a short working distance – Get a focuser. More about focusers
  • For a longer working distance – You will need a collimated LED or a fiber collimator. More about collimators.
  • For a medium size spot at medium working distance – Get a custom focuser. Contact us to discuss.

Long Answer:

Here is some general information about collimators and focusers, the difference between them and how to use them to project light to a target.

About collimators:

A collimator takes light coming from an emitter, and expands the light and sends it forward in relatively parallel rays. In other words, it is the thing that turns a bulb into a projector. Without the collimator the light would diverge and the power (which is a constant) would be diluted in space. Read more about collimation and divergence here.

In the images below you can see how the light would spread without a collimator and how the collimator keeps this from happening:

Here is a diagram that shows how the rays of light travel. The ideal distance from the emitter (in this case the emitter is the tip of the fiber) to the lens is the focal length (f). Every lens has a predefined focal length.

This diagram is theoretical. In practice the rays of light will diverge. The larger the emitter the wider the angle of divergence will be as explained in detail on the Appendix section of the collimator page.

Besides for projecting light, collimators are useful when a system needs parallel beams such as when passing through dichroic mirrors and filters, tissue or when hitting a detector.

About Focusers:

By definition a collimated beam will always be wider than the emitter. A focuser adds another lens that reverses the collimation and reduces the beam to a spot of light. In the simplest arrangement, a focuser will image the emitter 1:1 onto the target. The laws of physics dictate that the spot of light through an optical system can never be smaller than the original emitter, so 1:1 image is the smallest spot possible. Other lens arrangement can be used to get larger than 1:1 spot size or to increase the working distance.

Here is an image of a 1:1 focuser.

Custom Focusing optics can be used when the target size is larger than the emitter or the working distance needs to be longer then the focal length of the collimating lens. Contact us to discuss your requirments.

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