Getting to know the principles of stray light reduction is key to getting accurate measurements while working with your optical device.

Whether it’s a telescope, microscope, a chronograph or even a spectrometer.

If you use any of these optical instruments for important measurements or tests, get prepared to find out how to reduce stray light.

Why stray light control is important?

Optical instruments play a crucial role in technological enhancements, not only in the field of optics but in many others as well, from medicine to astronomy.

Present-day achievements would not have been possible if it weren’t for microscopes, telescopes, spectrometers and the list goes on.

The precision of these instruments is directly related to the accuracy of test results, measurements and the decisions made based upon them.

While working with these instruments, many factors are taken into consideration.

For example, the external environment can drastically alter tests and their results.

One of the most influential external factors that causes inaccurate test results is the phenomena “Stray Light”.

Stray light is one of the most common criteria that cause optical devices to fail to produce accurate test results.

It is therefore essential to find the correct and most effective way to minimize or block stray light completely to avoid the inaccurate measurements and their adverse effects.

The term “stray light” refers to any unintended light in an optical system.

It can be from an unintended source or an intended source through an undesired path.

Stray light can influence photometric precision and accuracy.

Microscope, telescope and spectrometer

How does stray light effect microscopes?

Any stray light signal can induce noise and fluctuations in sensor results contributing to errors in the desired measurements.

As stated stray light can affect many optical devices; it can affect microscopes, telescopes, chronographs as well as spectrometers.

All these applications follow the principles of optics and the presence of stray light signals may affect their measurements and in other cases also the manner of implementation of specific equipment.

Examples: In medical microscopes, stray light can reduce image contrast
[source: https://www.microscopyu.com/techniques/phase-contrast/specimen-contrast-in-optical-microscopy].

This produces a difference between the actual object and its microscopic image which is a matter of great concern.

How does stray light effect spectrometers and space telescopes?

The level of stray light is very critical for spectrometers as it can limit the ability of an instrument to measure the intensity of light.

As a result, the test results of a spectrometer can have narrow and intense absorption bands.
In samples under testing, stray light may cause a false reading to be recorded.

In space telescopes, the glow of stray light from the sky can limit their ability to detect far away and faint objects.
The detectors used in these optical instruments respond to all of light that reaches them.

Stray light is also responsible for a decrease in light absorbance ability and reducing the linearity of the instrument.
In a small camera, stray light can cause a minor loss, but in a space telescope, it can result in the loss of a massive amount of data worth millions of dollars.

It is therefore very important, correct and prevent stray light, minimizing the chances of error in optical instruments.

Methods of stray light reduction

Many methods for correction have been proposed. Most of the solutions regarding stray light problems emphasize stray light simulation and analysis.

Stray light can easily be simulated merely by taking the signal at every wavelength and its contribution to other wavelengths.

The simulations can be used to estimate the value of error which is associated with stay light.

Stray light can be corrected through efficient designing of baffles and other blocking components, real-time adjustments to the optical systems and last but not least, by using light absorbent coatings and materials.

Baffles and other mechanical designed system’s principal function is to restrict the light coming from unintended sources outside the device’s field of view (FOV).

A baffle is composed of a tube, with vanes in its internal walls. These vanes reduce the light intensity reflecting off the walls of the tube.

Efficient baffling is necessary for reduction of stray light entering the optical instrument.

Some of the disadvantages of this solution include the need for precise designing, cost and added weight to the device.

Careful design of baffles can be supported by using black light-absorbing materials to reduce the effects of stray light.

Excess stray light in an optical system can reduce the noise ratio (SNR), which is major degradation of an optical system.

If any element of an instrument can minimize the stray light from striking the plane of the image, this can increase the SNR and reduce the noise.

A black coating can provide a surface that can significantly reduce the reflected light by absorption.

The solution to have

We provide super black materials for the blackening of optical and mechanical components.

We also provide an Ultra Black coating services for light trapping applications such as light baffles, UV sensors, passive infrared detectors, light detectors, UV absorbers, etc.

Coatings are vacuum deposited to custom 3D parts of all substrate materials such as plastic, glass, ceramics and metals.

Coatings are space-qualified, inorganic, thin, RoHS & REACH compliant, biocompatible and low outgassing.

Our Metal Velvet black thin foil is the world’s best and blackest industrial coating with than 1% total reflectance at the 10nm-1,000nm wavelength range and extremely low reflectance at IR range up to 100um wavelength. Moreover, their coatings are a simple and cost-effective solution of stray light in a DIY manner, i.e.
the products supplied are ready to use and can be simply ‎bonded in the desired surface easily.

We also offer a unique material intended to suppress stray light from grazing angles best known as Hexa Black.

The Blacker The Better

Applying black coating on measuring instruments not only improve their ability to reduce stray light, but it can also improve overall surface smoothness and resistance against corrosion.

Moreover, if you are going to use your equipment under extreme temperatures (high or low) like in space environment, black coating of your optical equipment is a great idea.

In the light of above discussion, we can conclude that, by adhering to the principles of working with stray light and using advanced and adaptive coatings, it is possible to significantly minimize its effect resulting in more accurate measurements and tests.

The above suggested method is cost effective, easily applicable and most important efficient in stray light suppression!

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