How to test cutoff frequency of IR filter on camera?

[pgpgpgpg]

Modern cell phones seems to come with IR filters on their cameras. I want to do an experiment to figure out what wavelengths these filters allow to pass and which they block. How would I go about doing this?
Also, what sort of equipment would I need? I am a university student so I have access to a nicely supplied physics lab. Thanks.

 

[UltrafastPED]

Remove the filter; using a broad-spectrum source (e.g., a tungsten lamp) take a spectrum.
Now insert the filter and take another spectrum.

This will show you the attenuation for all wavelengths, and those which are blocked completely.

Your lab should have a well-calibrated light source and a spectrometer. If the equipment is modern it will be fiber coupled; if it is older there will be gratings inside, and you will have to use some optics to collimate the light into the spectrometer slit.

 

[Andy Resnick]

Alternatively, use the output of a monochromator to illuminate the sensor, compare the monochromator output intensity with the image intensity to (approximately) determine the cutoff wavelength.

You shouldn't have to go much beyond 700nm- no fancy IR equipment is needed. Same on the UV side- you should not have to go much below 400nm.

 

[UltrafastPED]

Alternatively, use the output of a monochromator to illuminate the sensor, compare the monochromator output intensity with the image intensity to (approximately) determine the cutoff wavelength.

We pop the filters off from cheap web cams so that they can pick up near infrared (700-850 nm or so) in our laser lab. But if you plan to put it back, you may prefer the non-destructive route.

 

[sardar]

To test the cutoff frequency of an IR filter on a camera, you will need to use a spectrophotometer. This device measures the intensity of light at different wavelengths and can help determine the specific wavelengths that are allowed to pass through the IR filter.

To begin, you will need to set up your camera and IR filter in front of the spectrophotometer. Make sure the spectrophotometer is properly calibrated and set to measure the intensity of light in the infrared range.

Next, you will need to take a series of measurements with the IR filter in place and then without the IR filter. By comparing the two sets of measurements, you can determine the wavelengths that are being blocked by the IR filter.

You can also use a known light source with a specific wavelength in the infrared range to further test the filter's cutoff frequency. By measuring the intensity of the light with and without the IR filter, you can determine if the filter is allowing that specific wavelength to pass through or not.

In addition to a spectrophotometer, you may also need other equipment such as a light source, a tripod to ensure consistent positioning of the camera, and a computer to record and analyze the data.

As a university student, you may also have access to other advanced equipment such as an infrared camera or a Fourier transform infrared (FTIR) spectrometer, which can provide more detailed information about the IR filter's properties.

In conclusion, to test the cutoff frequency of an IR filter on a camera, you will need a spectrophotometer and other equipment to accurately measure the intensity of light at different wavelengths. With proper setup and careful analysis of the data, you can determine the specific wavelengths that are allowed to pass through the IR filter and those that are being blocked.