Goldstone Scientific Blog

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

Posted by

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 Prizmatix.com 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.

View Comments


​Collimation and Divergence, in Fiber Optics and Collimated LEDs

Collimating the light of an optical fiber or LED is crucial for efficient light delivery and also improves the uniformity of the light when it hits the target. In a previous blog post we discussed the importance of matching the numerical aperture (NA) of a collimating lens to the NA of the optical fiber. [...]

Read More »


Popular Configurations - Fiber Coupled LED for In Situ NMR Spectroscopy

One application that is gaining popularity is a fiber coupled LED for NMR Spectroscopy. The set up that most people ask for is a Mic-LED and controller with fiber coupler adapter and a long plastic fiber optic. This set up can be seen in the “Supporting Info” section of these two papers: “Discovery of a [...]

Read More »


Prizmatix’s Advice on Light Meters for Optogenetics

I am often asked to recommend light meters to use for testing the fiber optic implants that will be used in Optogenetic experiments. This is important in order to test the quality of each implant and make sure everything is working correctly. Measuring the light correctly is not a trivial matter. The meter setting, the detector and [...]

Read More »


High NA Fiber Optics for In-Vivo Optogenetics – The Options on Goldstone Scientific

Quality fiber optic implants are crucial for successful in-vivo Optogenetics. Scientists will need to spend time or money (or both) to ensure quality results. Prizmatix offers a range of options and Goldstone Scientific makes it easy to order and offers competitive prices with bulk discounts and fast shipping to save you both. Many items are [...]

Read More »


Light Meters, Fiber Optics and Optogenetics – Part 2 – Bad Detector Advice

One of our customers was recently shopping for a light meter and detector. I had recommended a particular meter and a detector with a silicone photodiode from a popular vendor. The vendor advised that a detector with a thermal sensor would be better for an LED light source.Our engineers looked at that sensor, and advised it would [...]

Read More »


Light Meters, Fiber Optics and Optogenetics – Part 1 – Light Meter Blues

Prizmatix LEDs are extremely powerful and our customers are generally very satisfied with their performance.  Sometime, however, I get complaints about the power output being lower than expected as per the published specification. Very frequently it turns out that the light source is fine, and the problem lies within the tools and methods used to measure the power. In [...]

Read More »


High NA Fiber Optics and Collimators; Don’t Shoot Yourself in the Foot

A customer recently complained that the power output of her Prizmatix fiber coupled LED was too low. The LED system was 5 years old and she suspected that the power loss was due to age. She wrote: I'm using a  Prizmatix FC8-LED fiber coupled multi-channel LED source, along with a fiber that we purchased from you. This fiber is attached to a custom-made [...]

Read More »


Understanding Prizmatix Model Names – A concise guide

Prizmatix recently updated their model names and part numbers to make it easier to understand which model fits which application. This guide will help you understand what each section of the part number means. UHP – Any light source model with UHP is Ultra High Power. This means that the LED chip is being driven with an electrical current [...]

Read More »


Prizmatix Fiber Optic Rotary Joint; Compatibility of with Lasers or other light sources

The Prizmatix Fiber Optic Rotary Joint is an important part of the Prizmatix  In-Vivo Optognetics Toolbox. It’s extremely low torque (<10μNm) allows even the smallest animals to move freely and its high transmission is helpful in getting as much power as possible to the target. One really nice feature of the Prizmatix fiber optic rotary joint is that it can be used [...]

Read More »