Why can some cameras still shoot infrared without removing the internal IR-cut filter?
Asked 8/2/2012
5 views
2 answers
0
I’m trying to understand how a camera sensor responds to infrared light. I used a 760nm IR-pass filter on two compact cameras:
- Camera 1 had its internal IR-cut filter removed, and it captured IR images more easily.
- Camera 2 still had its factory IR-cut filter in place, but it could still capture IR images through the same 760nm filter, just with longer exposure.
So why does this happen? If a camera can still record infrared without removing the internal IR-cut filter, what changes between these two setups? Does removing the internal filter change the sensor’s wavelength sensitivity, or does it mainly increase the amount of IR reaching the sensor and reduce exposure time?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
2
The factory installed IR cut filter on most digital cameras is very thin, and whilst it cuts out most of the unwanted IR spectrum, some IR light does get in. Screw in IR pass filters designed to go on the front of the lens are thicker and usually better at stopping light from the visible spectrum.
So what is happening in the second case is that you are using a good IR-pass filter combined with a weak IR-cut filter, so no (or very little) visible light gets through the first filter but some IR light gets through the second, hence you're able to get IR photos.
The strength of the factory fitting sensor IR cut filter varies between manufacturers and models, some have very weak filters and are thus prized by people who want to dabble in IR without going through the expensive or risky filter replacement option.
You will get slightly different frequencies transmitted with both filters in place, but fundamentally the advantage to removing the sensor filter is that exposure times improve (quite drastically if the IR filter was strong to begin with). In some cases it can go from 10 seconds (requiring a tripod) to 1/200s (allowing hand held shooting). With a DSLR not having a visible-light cut filter on the front of the lens allows the viewfinder and autofocus to work as normal, which aids composition and general shooting!
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
14y ago
0
Generated from our catalog & community — verify before relying on it.
Removing the internal IR-cut filter does not change the sensor’s native sensitivity. It mainly changes how much infrared light reaches the sensor.
What’s happening is:
- The front 760nm IR-pass filter blocks most visible light and lets mostly infrared through.
- The camera’s factory IR-cut filter is not always a perfect blocker. On many cameras it is relatively weak, so some IR still passes through it.
- With the internal IR-cut filter removed, much more IR reaches the sensor, so exposure times are shorter and IR shooting is easier.
- With the internal IR-cut filter still installed, less IR reaches the sensor, so you can still get an IR image on some cameras, but with longer exposures.
So the difference is mostly overall transmission of IR light, not a change in the sensor’s spectral sensitivity. The strength of the built-in IR-cut filter varies by camera model, which is why some cameras work better for infrared than others even when unmodified.
Recommended products
UniqueBot
AI14y ago
Your Answer
Related Questions
Do point-and-shoot cameras use a separate metering sensor, and how does IR conversion affect focus?
Can a full-spectrum digital camera produce separate RGB and near-infrared channels from one RAW file?
Why do DSLR IR-cut filters often block some deep red light below 650nm?
Why do cameras use an IR-cut filter if the Bayer color filter is already on the sensor?
Why doesn't my Canon EOS 1000D record IR light after removing the IR-cut filter?