You may have noticed the so called adjustable variable infrared filters that are popping up on Ebay and elsewhere online. Here is one example:
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So how do these adjustable IR filters work and are the results any good?
Although the concept is intriguing in reality though the results are quite poor and it’s all due to physics. The way these filters are made is by taking a simple variable ND filter, which is a sandwich of 2 types of polarizers and adding a red longpass filter on top of the stack. At this point some of you may already have figured out the issues just from reading the previous sentence. That’s right, all the problems you experience with variable ND filters transfer over and are made worse with the capture of two different light spectrums, visible and infrared.
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The dreaded cross pattern is just as bad here, gets progressively worse the stronger IR effect you dial in. Also, because of the qualities of stacked polarizing filters you also induce a lot of softness to the image, washing out fine detail considerably. I guess if these effects is what you are after then great, this is a perfect filter for you but for the general photographer who is seeking the finest image capture possible this filter just isn’t a good idea.
Don’t believe me? No problem, go buy one and try for yourself, heck they come from China so are cheap enough for a simple experiment right? Here is an Ebay listing full of them.
For those that still want to be able to adjust the IR effect in camera you’d be best served by using our external IR filters in front of the lens. Just remember this point: you can override your internal (in camera) IR filter by using a STRONGER external IR filter over your lens but not the other way around. So if you are starting with a Super Color IR Conversion (590nm) then placing any of these over your lens will work: Enhanced (665nm), Standard (720nm) and Deep BW (830nm). So as long as the wavelength outside is higher than inside it will work with great results. It’s like having multiple conversions all at the same time.
The only drawback is for people without Live View because IR filters are quite opaque you’d be blocking your viewfinder in your DSLR, of course cameras with Life View and all Mirrorless cameras don’t have this problem as the sensor sees through the filters just fine.
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