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How Do Filters Work in infrared/ full spectrum camera?

Sunday, July 3, 2011

We add filter to add its color to our image? Well not always like that in infrared photography. We can refer to traditional photography, why a black & white photograph need a filter red, yellow, orange, while the result is black and white? It is a misconception to think that a colored filter adds its color to an image. The main idea of colored filters transmit wavelengths that are a similar color to the filter and block ones that are not. For example, uunder tungsten light which rich red an yellow tone, a blue filter that's used to colorcorrection it doesnt intended to add blue to the image. It subtracts the red and yellow tones, so it rendering the image more neutral. This happen on traditional photography. While in digital this filter can be replaced with custom white balance.
In much the same way in digital infrared, the various deep red filters used for infrared photography,are intended to totally or partially absorb visible light while allowing the transmission of infrared light. This will give you a nice white leaf while other are change to colorless, because most color absorb by the filter.
So what is the effect if we put color filter in front of full spectrum camera
here it the example
first take alook at the full spectrum image

As you can see the leaf will looks brown, the green leaves reflect infrared and make the color change
Blue filter 
Blue filter will reduce the reddish effect while other are still looks same
creating a yellow leaves and enhanced the blue sky, my favorite filter.
Red filter
the red block most of color, but not over all, the result is very different from what we see in normal eyes
It will give you interesting effect, and with further process you will get more dramatic result

The infrared filter
The infrared filter block almost all color, leaving a white leaf, the result is very different from what we see in normal eyes, a traditional look of infrared images.

The color filter and IR filter is a round piece of glass within a metal or plastic mount that allows it to be threaded on the front of a DSLR / prosumer lens. The most famous is hoya filter (hoya R72 for infrared) , there are other but non common like Green L. These filter are sold in various sizes to mount directly onto different sized lenses. This one is expensive and depend on the lens filter thread.

Other color/ IR filter type are square filter. The famous one is cokin (cokin P007 for infrared) other like Hitech IR, is made from high quality resin, the cheaper ones is tian ya filter ( all my color filter use the  tian ya, only the infrared, i use cokin or hitech, never use hoya because it too expensive).  The square filters are attached with Cokin modular concept, a system which includes a holder that attaches to the front of the lens with an adapter ring. The system's square filters slip into the holder. We may need different sized attachment rings to fit your various lenses, you won't have to buy a different IR filter for each lens because the same holder and filter can be used with different sized adapter rings. More economic, but bulky on lens. This system is adopted by Chinese brand filter tian ya and green L.

All this filter is not intended to attach to pocket pocket camera, so if you want to attach it, you need to be more creative. See my camera to know how to attached the filter in front of pocket camera


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