What’s the difference between an infrared filter and an ND filter for photography?
Asked 4/5/2019
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2 answers
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I’m confused about the difference between an infrared (IR) filter and a neutral density (ND) filter. I already have a Big Stopper, but I’d like to try infrared-style images. I’ve seen photos where foliage looks bright or unusual in tone, and I’ve also seen “white hot” heat-source images. Can an ND filter do that, or do I need a specific IR filter? Is there a recommended lens filter for this kind of photography?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
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ND stands for "neutral density" - it is a filter type that (in theory) absorbs all wavelengths of the visible light by the same amount.
Effect of a ND-filter. CC-BY-SA 2.0: Robert Emperley
IR filters filter out all but certain wavelengths - the (near) IR wavelength of the filter. So basically, they are IR-pass filters, not IR-block filters. Thanks @TheLuckless!
As @Hueco states in his comment, IR filters will cut everything below a certain value. That value might be between 650 and 720nm - visible light, however, does go up to 750nm. Thanks for clarifying that, Hueco!
Typical result of using an IR filter. Some effort was put into post-production: The red and blue channels were swapped. CC-BY-SA 2.0: Jannis
What you think of (white heat source, everything else red-ish) is most probably a thermographic camera - they differ from regular cameras in a lot of ways, including lenses that are (typically) made out of Germanium.
Thermographic image. CC-BY-SA 3.0: Lutz Weidner
Originally by user69369. Source · Licensed CC BY-SA 4.0
user69369
7y ago
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Generated from our catalog & community — verify before relying on it.
An ND filter and an IR filter do very different jobs.
An ND (neutral density) filter is meant to reduce the amount of visible light reaching the sensor, ideally evenly across the spectrum. It mainly lets you use longer shutter speeds or wider apertures in bright light. A Big Stopper is an ND filter, not an infrared effect filter.
An IR filter is an IR-pass filter: it blocks most visible light and passes near-infrared wavelengths. That’s what’s used for infrared photography effects such as bright foliage and dark skies. Those classic IR images often also involve post-processing, such as channel swapping.
The “white hot heat source” look you mention is generally thermal imaging, which is different from normal photographic infrared. Standard camera IR filters do not turn a regular camera into a thermal camera.
So if you want infrared photography, you need a dedicated IR-pass filter, not just an ND filter. Common IR filters cut visible light below a certain wavelength and pass near-IR. Your results will also depend on how much IR your camera sensor still records.
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AI7y ago
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