In Part I,  Tim Shoebridge introduced the Sigma SD Quattro as an ideal camera for infrared photography. Part 2 he reveals how he setsup the SD Quattro for infrared and how to get the best out of it.

                             ‘Using a mirrorless camera such as the SD Quattro takes all the guesswork out of obtaining focus with infrared imaging.’

To shoot infrared on the SD Quattro you need to remove the hot mirror from inside the camera lens mount and fit an infrared filter to the front of your lens. There are a variety of infrared filters you can use and it is worth experimenting with different filters to find the one you prefer.

The infrared images shown here were shot using a 720nmfilter, which is a common choice and considered middle ground for infrared photography. I use a filter holder system and obtained 100mm square infrared filter which is compatible with it. This set-up is really useful when swapping lenses but you need to make sure there is no chance of light leaks when fitting the filter in the holder.Infrared has traditionally been a B&W medium, but the advent of digital cameras has created popularity in colour infrared imaging too. For practical purposes I recommend that the SD Quattro is a camera for B&W infrared capture only.

The Foveon sensor in the SD Quattro records colour information in a unique way compared to mainstream Bayer sensors, and infrared light will almost exclusively be recorded by the Foveon sensor in the red channel to a greater degree of accuracy than a Bayer sensor. Given that the Foveon sensor captures pure infrared images as shades of red, it is not possible to achieve a white balance that properly supports colour imaging.

I do not see this as a bathing, my preference is for black& white infrared images over colour ones and colour can still be achieved with the SD Quattro when using wider spectrum filters or capturing full spectrum images. So when capturing infrared images on my SD Quattro I set the colour mode to Monochrome, and within that mode I set contrast to maximum, the filtering effect to red and dial the sharpness down to minimum. These settings give me the strongest images and the best starting point for further editing in post-production.
Obtaining correct exposure has always been a problem in infrared photography, and although modern digital camera exposure meters are incredibly sophisticated, they are designed to measure visible light, not invisible infrared radiation. The Sigma SD Quattro helps take some of the guesswork out of exposure, since you have a live preview of the image on held and in the EVF.
However, even this live preview is not a completely accurate representation of the image and it will require some testing to determine what adjustments to make. With my set-up and the particular IR filter I use, the camera generally overexposes infrared images by between two-thirds and one stop. So when I have the live view and histogram looking exactly as want, I know I need to reduce the exposure by up to one stop to ensure the captured image exposure matches. I must stress this is for my particular set-up, the adjustment you make will be dependent on the IR filter you are using as well as the lighting conditions and your subject. Comparing the histogram before and after capture is simple way to determine the adjustment you need.
 

Understanding how the final image exposure is likely to vary from what the camera’s metering system thinks it will be becomes important when considering exposing to the right (ETTR). Relying on the live view histogram alone when employing an ETTR technique is likely to create clipping in your final image when shooting infrared, in my case by up to one stop.
So why use ETTR for infrared photography? First, it is almost exclusively the camera sensor’s ‘red’ photo sites that record any information. This means the total amount of usable data recorded by the camera sensor for infrared images is significantly less than for regular visible spectrum images, and is a general problem for both Foveon sensors and Bayer sensor converted cameras. Second, the infrared spectrum is much narrower than the visible light spectrum, which is why infrared images are naturally very low contrast and flat. Infrared images are prone to noise but by ETTR we have the best chance to eliminate that noise.

Using a mirrorless camera such as the SD Quattro takes all the guesswork out of obtaining focus with infrared imaging because what you see in terms of focused image through the EVF is what you get in the captured image. I usually focus manually but I have tried autofocus on the SD Quattro when shooting infrared and it worked very well.

But as with any digital camera, you need to bear in mind that the job of any camera plus lento obtain auto-focus is made more difficult with infrared so perfect auto-focus operation is not guaranteed every time.

I strongly recommend you try infrared, it can provide wonderful opportunities to capture images when lighting conditions for traditional photography are not favourable. And with the Sigma SD Quattro you have two cameras in one – it really makes shooting infrared opportunistically practical reality.

 
Click here to view PDF of the original article from Black & White Photography magazine