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Blue Glass Optical Filters

Sep. 11, 2023

Blue glass optical filters

Blue glass optical filters have dramatically improved the quality of photos, but back-illuminated cameras with embedded blue glass filters are becoming popular on high-end phones with 8 megapixels or more. In this article, we will talk about the role of blue glass filters in detail.

Infrared light affects imaging quality

According to the principle and law of refraction of light, it can be concluded that: the longer the wavelength, the smaller the refractive index; the shorter the wavelength, the larger the refractive index. Therefore, when these rays of light enter the cell phone camera at the same time and are refracted by the lens, visible light and infrared light will be imaged on different target surfaces. The visible light is imaged as a color image, while the infrared light is imaged as a black and white image. When we adjust the visible light into the image, also known as the image focus and back focus adjustment, then the infrared light will form a false image in this target surface, thus affecting the color and quality of the image.

Blue Glass Optical Filters

Effectiveness of Blue Glass Filters

To avoid the false image of the target surface caused by infrared light, the most effective means is to filter infrared light by IR Coating or pretending filter to restore the true color of the object, so as to solve the problem of image color distortion.

The difference between blue glass and other filters is that the raw material is different. Blue glass is made of blue glass as the raw material (ordinary filters are general optical glass), and its effect is to filter infrared light by absorption.

Due to the high transmittance of the blue wavelength, it has better penetration than red-orange glass filters, filtering infrared light above 630 nm (but allowing the rest of the light in a very broad band from UV to IR to pass through) and filtering it more thoroughly. It is important to note that while blue glass filters filter infrared light, there are no filters available that make objects image brighter, as all filters absorb certain wavelengths and darken objects.

For this reason, blue glass filters are often also coated with AR Coating, which is designed to increase light transmission and reflect infrared light. As we all know, light will be refracted and reflected when passing through different media, after adding single AR Coating, the filter will increase the light transmittance by 3~5%, if adding double or even four layers of AR Coating, the filter can reach more than 98% light transmittance, which will make the image clearer and make the filter less prone to fogging. On the other hand, without AR Coating, the light transmittance of the filter will be lower than 90%, which will significantly reduce the sensitivity of the camera and thus affect the image quality (very dark images).

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