Polarizers are filters that remove reflections at certain angles. Sony Semiconductor Solutions has developed a sensor that can calculate the direction and degree of polarization in real time.
Polarizing filters are used to control (both hide and produce) polarized light. PL filters for Single-Lens Reflex camera and polarized sunglasses may be familiar use cases. As polarizing filters remove reflection light, they are essential accessories for photographers and videographers, who use them for turning captured color vivid or looking inside water. From skies to landscape, water surfaces to shop windows, polarizers are ubiquitous pieces of hardware.
The problem with polarizers is that they only work when certain conditions are met: the norm is that the degree of polarization depends on the angle of reflection. If the degree of polarization is low, reflected light cannot be removed clearly. To remove reflected light clearly, it is important to pay attention to the angle of reflection so that the degree of polarization is high. How many times have you wished there were better ways to control polarization? Well, a company may have a solution.
Sony recently released some videos demonstrating the reflection removal performance comparison among cameras using no filter, polarizing filter and Sony’s Polarization Image Sensor. Under the name PolarSens, the company has researched solutions to control reflections through the use of polarization. The technology allows Sony’s polarizer sensor to remove reflections from various planes and that can be done at the same time, which is something totally different from what’s possible with a regular polarizing filter.
PolarSens, a Sony technology
Since 2020 that Sony has published a series of videos with application examples of polarization image sensor: reflection removal, visual inspection, improve visibility, 3D/Stress detection and human/vehicle detection. While the technology used in PolarSens is developed with industrial uses in mind, it’s an interesting solution that may, someday in the future, make it to consumer and professional cameras used by content creators.
Now, polarization sensors already exist, but while conventional types of polarization sensors the polarizer is attached on top of the on-chip lens layer, Sony Semiconductor Solutions’ polarization sensor – PolarSens – is different: the polarizer is formed on chip under the on-chip lens layer. A shorter distance between the polarizer and the photodiode improves, says the company, “the extinction ratio and the incident angle dependence.”
Extinction ratio, which is a specification to measure polarization, needs some explanation. The extinction ratio of polarization image sensor is the ratio between the sensitivity of transmission axis light and the sensitivity of extinction axis light (the sensitivity of transmission axis light / the sensitivity of extinction axis light). The higher the number, the better the specification and performance.
Now back to the polarizing sensor PolarSens from Sony. The company claims that “since the polarizer is formed during the semiconductor process, form and formulation of polarizer, uniformity, mass productivity and durability are excellent compared to conventional polarization sensors. Furthermore, Sony Semiconductor Solutions’ Polarization sensor is covered with an anti-reflection layer which helps to reduce reflectance and avoids poor flare and ghost characteristics.”
Three PolarSens CMOS polarizer sensors available
Sony Semiconductor Solutions’ polarization sensor can capture a four directional polarization image in one shot by the four directional polarizer. It can calculate the direction and degree of polarization (DoP) based on the intensity of each directional polarization. Together with subsequent signal processing, it can capture the polarization information in real time.
The videos published recently by Sony demonstrate the reflection removal performance comparison among cameras using no filter, polarizing filter and Sony’s Polarization Image Sensor, showing the results with the camera set to the side and in front of the subject. There is also a White Paper, The Principle of Reflection Removal Utilizing Polarization and Features of Polarization Image Sensor which can be download by anyone who wants to know more about the technology. Again, remember that the initial application of the sensor has nothing to do with image capture as photographers and videographers see it. Still, there is always hope that the technology may be useful in more ways than those where it is now being applied.
Sony Semiconductor Solutions has launched a PolarSens polarization image sensor (polarization sensor): 3.45μm pixel size with four-directional polarizer which is formed on the photodiode of the image sensor chip. This polarization sensor is targeting the industrial equipment market. In addition to capturing brightness and color, this image sensor can also capture polarization information that cannot be detected by a normal image sensor. This polarization sensor can be used in many applications in the industrial field, such as inspection when visibility and sensing are difficult.
Sony has three CMOS polarizer sensors available, the IMX250MZR / MYR and IMX264MZR / MYR, with approximately 5.07M-effective pixel monochrome/color and the IMX253MZR / MYR with approximately 12.37M-effective pixel monochrome/color, both with Global Shutter function and high-frame rate, features also needed for industrial applications.
Cross polarization is a technique that uses two polarizing filters – one on the light source and on e on the camera lens – to get rid of unwanted specular reflections.
This article is part one of a two-part series explaining cross-polarization and birefringence.
Understanding Polarized Light
So let’s have quick look at the science of it: light is a form of electromagnetic radiation, meaning that it consists of waves, oscillating perpendicular to its direction. But those waves are not aligned; some of them oscillate up and down, some move left and right, and still others all directions in between.
That is, of course, unless we are looking at polarized light.
Polarized light waves are all oscillating parallel to each other, meaning they all share one plane. To polarize unpolarized light, we can use a circular or linear polarizer, which only lets the light of one certain plane pass while light waves that are oscillating in a different direction we’ll be reflected.
Two polarizers that are aligned perpendicular to each other don’t let any light pass.
This is the same principle that variable ND (neutral density) filters use to block out varying amounts of light. Such filters consist of polarizing filters, one of which is stationary, while the other one can be rotated against it, which gradually blocks out more and more light until the two filters are aligned perpendicular to each other and effectively block out all light.
This gets really interesting when we are directing our polarized light source onto our subject. As the polarized light hits the surface of that subject it becomes reflected and most of it turns into diffused, unpolarized light again except for the specular component of the reflection, which is still polarized and can therefore be canceled out by employing a second polarizer (CPL) filter in front of our lens.
The result leaves us with a very clean looking image.
You can try this out at home, even if you only have one CPL filter in your camera bag; due to the way that LCD displays work, they emit polarized light by their very nature, so all you need to do is to load an empty word document or a white wallpaper and you’ll be able to see the effect of cross-polarization right away.
Even though this is a very useful technique to have in your toolbox, it isn’t the only interesting application of cross-polarization.
It can also be employed to create images like this:
In part two, we’ll discuss more about birefringence and how to create colorful images utilizing it.
About the author: Maximilian Simson is a photographer and artist based in London, Ontario. The opinoins expressed in this article are solely those of the author. You can find more of Simson’s work on his website and Facebook. This article was also published here.
Kolari Vision has just unveiled a line-up of high-end, ultra-rugged drop-in filters for Canon’s special EF-to-RF mount adapter with a built-in filter slot. According to Kolari, not only are these the first third-party drop-in filters actually shipping to consumers, they’re also some of the most durable and high-quality filters money can buy.
While Kolari is first to market, they are not the first to announce a third-party option for Canon full-frame mirrorless users. That distinction goes to Breakthrough Photography, who unveiled their drop-in filters at the beginning of August.
But speaking with Kolari Vision owner Ilija Melentijevic, he tells PetaPixel that there are several important reasons why you might want to consider their options, and not just because you can buy them right now (Breakthough’s filters don’t ship until September 25th).
According to Melentijevic, there are five main reasons the Kolari filters stand out:
- Ours is CNC machines aluminum
- We use a gorilla glass substrate for the ND filters, the only one of its type.
- We’re aiming for the top with our ND filters in general, and have the data to show our 10 Stop is flatter than anything else on the market, even Breakthrough. We’re investing aggressively and won’t stop until we have the best filter in every category.
- We offer more options for multi spectral. Breakthrough is offering one 720 filter, we will be offering a series designed for full spectrum cameras including 590, 665, 720, ultraviolet, and our IRChrome. This will open up UV and IR to lenses for which no filter currently exists.
- Maybe most distinctly, we are launching in parallel here a clip filter system for the RF mount that can be used in tandem with the drop in, or alone with native lenses, offering potentially two spots behind the lens to put filters for extra combination options.
Alongside these filters, the company is planning to introduce some specially modified and calibrated unfiltered versions of the Canon EOS R5 and EOS R6, where they put the IR filtration into the clip filter instead of modifying the sensor. This allows for a user-interchangeable OLPF system like some RED cameras have and some Sigma DSLRs had in the past.
As of this writing, you can already order Neutral Density, Infrared, Ultraviolet, IR/UV Cut, and IRchrome filters, with a Circular Polarizer and Variable ND filter listed as “Coming Soon.” In terms of pricing, the filters range from $100 for the various IR filters and the IR/UV Cut filter, to $150 for that 10-stop ND filter, all the way up to $300 for the UV bandpass filter.
To learn more about any of these drop-in filter options—and their clip-in counterparts—or if you want to order your own, head over to the company’s website.