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.