Guide to digital infra-red (IR) photography

Introduction

Conventional (visible light) photography is the formation of images with light at wavelengths from 380nm to 750nm.

Infra-red (IR), or more correctly known as near infra-red (NIR), photography is the formation of images with humanly-invisible light at wavelengths from 750nm and above. Most IR photography involves wavelengths up to 1200nm. IR photography is done with a very dark (opaque-looking) IR-passing filter which could be made of glass or plastic.

Generally, there are 2 broad methods to produce IR images with digital cameras. First, the attachment of an IR-pass filter over the lens. Second, the attachment of an IR-pass filter replacing the imager (CCD/CMOS sensor) pass filter

IR filter over lens

Common IR-pass filters include Hoya R72, Cokin P007, Wratten 87, Wratten 87C. Darker, more opaque-looking filters transmit IR-light in the higher wavelengths and produce IR-images that resemble high-contrast black-and-white images.

Attachment of IR-pass filter over the lens is a cheap, but is a slow and troublesome method of doing IR photography. With a DSLR camera, composition and focus must be done before attaching the IR filter since the filter is very dark (causing a viewfinder black-out). Exposure times are a time-consuming guess work, and can be very long (maybe over 20 seconds) even on a bright sunny day, and made worse by in-camera long-exposure noise-reduction processing. In addition, many camera-lens-imager optical systems were not designed for IR transmission, resulting in hot spots (optical flare in the center) on IR images.

IR filter over imager

Attachment of IR-pass filter over the imager (by removing the camera?s visible light filter) requires skillful camera dismantling and precise focus calibration. These procedures can only be performed by a qualified camera technician. Very often, focus calibration requires the use of proprietary service software available only at authorized service centers.

With an IR filter over the imager, IR photography is faster and easier to do. Exposures are short (not requiring a tripod). Since the IR filter is attached over the imager, there is no viewfinder black-out with DSLR cameras, hence the feel of a normal (unmodified) camera. The occurrence of hot spots is unlikely, making many more lenses IR-compatible with DSLR cameras.

Starting IR photography with a dedicated digital camera

1. Obtain a digital camera to be modified into a dedicated IR camera. Most people use their old or backup digital cameras that are still in good working condition, Digital SLR or Compact camera.
2. Send your camera to ACS and a qualified camera technicians with specialized tools and proprietary diagnostic/calibration will dismantle the camera in a specialized clean booth ,the ban pass filter is removed and replaced with the dedicated IR filter and the auto exposure meter is altered to correctly respond to the same wavelength. Once the camera is assembled the focus is calibrated to best suite the main lens used with the camera.
3. When you receive your IR-modified and calibrated digital camera, you may shoot IR images almost as easily as normal conventional photography. Try Auto White Balance (AWB) first, or for better control over the results, use custom white balance (CWB) by measuring on a patch of grass/leaves or at the blue sky.

Advantages of a dedicated (IR-modified) digital camera

• Increased transmission of infrared light on to the imager results in faster exposures and lowered ISO.
• Fast exposure allows handheld photography and freezing of moving subjects. Fast exposures are also less susceptible to electronic noise.
• Lowered ISO images are less vulnerable to electronic noise, hence resulting in smoother and higher definition images.
• With a DSLR camera, composition and focus is possible through the viewfinder. There is no black-out due to an IR filter attached over the lens.
• With only an IR-pass filter fitted, visible light is eliminated in the captured images; hence optical interference from visible light is absent. This can result in sharper (properly focused IR light) and stronger contrast images.
• IR-modified cameras can be, and should be, focus calibrated for the IR spectrum since IR does not focus on the same focal point as visible light. Even in the visible light spectrum, red and blue do not focus on the same focal point.
• If the digital camera was modified properly with focus calibrated for IR, there is no need to manually compensate the focus. (Only the lenses within the calibrated range)

Colours & white balance

Using Auto White Balance (AWB), some digital cameras may produce IR images with a strong yellowish/reddish/brownish colour cast known as false colour. This is due to the characteristics of the imager and processing algorithms. Post-processing in Adobe Photoshop (or similar) is required to remove/reduce this false colour effect. False colour can be removed/reduced by shooting images with Custom White Balance.

Using Custom White Balance (CWB) measured on sun-illuminated grass/leaves (a ubiquitous available midtone), IR images tend to appear more monochromatic.

When using the Colour mode, random spots of colour (colour artifacts) may occur in images. If the camera has Black-and-White mode, using this mode will eliminate colour artifacts, and may strengthen the monochromatic appearance in IR images.

Generally, there are 4 possible combinations of photographic modes to shoot infrared images.

• Colour mode with AWB
• Colour mode with CWB
• B&W mode with AWB (unavailable on some cameras)
• B&W mode with CWB (unavailable on some cameras)

More false colours can happen with other white balance settings such as Tungsten or Fluorescent.

Post-processing of IR images

1. Open your IR images in Adobe Photoshop. Click Image > Adjustments > Auto Contrast if your images are underexposed due to the filter.
2. Click Image > Adjustments > Channel Mixer. Select Red Channel in Channel Mixer, slide your Red percentage to 0% and Blue to 100%. Now select Blue Channel in Channel Mixer, slide your Blue percentage to 0% and Red to 100%. The basic process is done.
3. You can still further tweak the colours to your desired effect.
4. To enhance whites/highlights:
   Click Image > Adjustments > Selective Colour. Select Neutrals. Slide the Black to a negative percentage to enhance whites/highlights. Experiment with the Method - Relative or Absolute.
5. To obtain a cyan-tint:
   Click Image > Adjustments > Selective Colour. Select Black. Slide the Yellow to a positive percentage.
6. To obtain a yellow-tint:
   Click Image > Adjustments > Selective Colour. Select Black. Slide the Cyan to a positive percentage.

Full Spectrum (Clear Filter) options

Full Spectrum (Clear Filter) options for those interested in the UV, Visible and IR spectrums. The prices for these filter options, including installation service, are the same as the pricing table above. We can also special order most filter variation that you may need. Some of our customers have ordered special filters covering narrow or wide areas of the spectrum for specialty photography, including Astrophotography, Solar photography, Fireworks photography and others. Also, we are constantly testing conversions on models that are not listed below. If you are interested in having a camera model converted that is not listed above please contact us as we may be able to accommodate your needs.

Light spectral range, most full spectrum converted D-SLR cameras are sensitive from 250nm to 1100nm.

Advanced Camera Services Limited

Unit 10 Linmore Court Threxton Road Industrial Estate Watton Norfolk IP25 6NG

T 01953 889 324 F 01953 880 086 ACS_2005@BTconnect.com