Near-Infrared Reflection? A mystery explored in the World of Infrared Cameras

Infrared

Digital camera and Near-infrared

Hi, I am Teppei at KOPRO product division.

As a feature of our anti-reflection material, "FineShut" series, "absorbing near-infrared" is one of our priding features.

 

First, what is near-infrared in the first place? Humans can visually perceive electromagnetic waves in the wavelength range of 380 to 750 nm. The short wavelength up to 380nm is recognized as violet while the long wavelength up to 750nm is recognized as red. Wavelength range exceeding red 750 nm is called infrared.

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There are 4 types of infrared rays : Near-infrared (750 ~ 1400 nm), Short-wavelength infrared (1400 ~ 3000 nm), Mid-wavelength infrared (3000 ~ 8000 nm), Long-wavelength infrared (8000 nm~). This time we'll focus on Near-Infrared.

 

As mentioned earlier, infrared rays are not visible. However, this changes a bit when it comes to digital camera sensors. The sensor of a digital camera has a wider wavelength range that can be captured by human eyes. This means that it captures infrared rays.

 

Therefore, (in many camera models) an infrared cut filter is attached in front of the sensor to attenuate the near-infrared and bring it closer to the human eye.

It seems that there is a difference on the design concept on which wavelength range to cut. Depending on the manufacturer, there are cameras that can easily see near-infrared (for example, Fujifilm X-trans CMOS). These cameras are especially popular with astro-photographers.

 

For this comparison, I removed the infrared cutting filter, and installed a visible light range filter (IIR76) to test out the near-infrared sensitivity and light reflection of the digital camera. Let me show you the results.

Difference in appearance of visible light and near-infrared

photo of a man holding Fineshut KIWAMI took by normal camera

I tried to take my picture in the middle of one fine day during spring. I wore my favorite Kawasaki cap and black Fleece sweater thinking I am a fashionable middle-aged man.

 

Joking aside, this is an example of a normal digital camera image. It was taken using Fujifilm's X-H1. I am holding a FineShut KIWAMI sheet (cut in a rectangular shape) with my left hand. The FineShut KIWAMI cannot be distinguished at all in this picture.

 

Take a look at the next picture. It is an image taken simultaneously from an infrared camera.

photo of a man holding Fineshut KIWAMI took by infrared camera

This means that the fleece jacket and cap were absorbing light in the visible light region and then reflected near-infrared rays. This results into an image where most of the colors changed to white. The plants behind me are also white, which is completely different from the picture above.

 

This time, you can also clearly see the Fineshut KIWAMI I have in my hand. This picture shows the effect of near-infrared in colors of a picture. 

comparison of photos took by normal camera and infrared camera

For the comparison, I made the original color photo into black and white. The difference is clear when you put them side by side.

 

The fleece jacket I wore this time was 100% polyester. In this way, even though synthetic fiber has high light absorption performance in the visible light range, it often reflects the close-range infrared in full. This shows that our FineShut KIWAMI is "strong in near-infrared!"

Product introduction of the fine shut series, please purchase from here!

>>Near-infrared total reflectance 1.2 to 1.8% Fineshut SP

>>Near-infrared total reflectance 0.7 to 1.1% Fineshut KIWAMI

Final thoughts

As mentioned above, I talked about the near-infrared in this blog.

It is commonly used for food and product inspection which is usually set with visible light. For example, sensors for automatic driving utilizes the function as a night vision camera. Optical use of near-infrared has received great attention in recent years.

 

However, recent anti-reflection material corresponding to the close-range infrared has been underdeveloped over the years. Our FineShut Series is a very effective and easy-to-use material, so I hope you take advantage of it.

 

Finally, I will also upload a photo of a shrine close to our company. Which is the infrared photo?  

See you on the next blog.

Photo of a Japanese temple taken by a regular photo
Photo of a Japanese temple taken by an infrared camera

>> CHECK Ultra black sheet Finesut SP and Fineshut KIWAMI pages!!

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