Hi Michael, thanks for the questions. It is important to understand how a photo is produced from an infrared converted camera to understand what one is seeing in the photo. I’ve provided some insight previously but I left out what you asked about even though it was a question I had when I started with IR photography.
More people have seen photos from thermal imaging cameras than from IR converted cameras. The two are very different from each other but it is easy to think they are similar. A thermal imaging camera uses a specially designed sensor that “sees” only in the longer wavelength/lower frequency Far Infrared spectrum. Far Infrared has much more energy than Visible Light and Near Infrared. I’m not sure how this works to produce an image but generally, in the end, colors are assigned to temperatures.
An infrared converted camera is a camera with a sensor designed for visible light. The design of the sensor produces an image that is flat across the spectrum of red through violet. In order to do this the sensor has a sensitivity roll-off into ultraviolet at one end and into near infrared at the other end. The sensor has an infrared blocking filter to keep the near infrared (a red cast) out of the image. One can purchase a UV blocking lens filter to keep out the UV (a violet cast).
The conversion to IR photography requires the removal of the IR blocking filter and the installation of a visible light blocking filter at the sensor. Because the sensor is designed for visible light it only has a sensitivity to the roll-off in Near Infrared and can not “see” anything close to the Far Infrared spectrum. Near Infrared images do not show temperature any more than Visible Light shows temperature.
However, to either confuse or clarify, visible light is given a temperature value. Light bulbs are often rated this way, so is white balance, both using the Kelvin scale of temperature. Blue light is called cool and yellow light is called warm. This corresponds to the energy levels across the electromagnetic spectrum. Can it be said that visible light is called such because it is a range of temperatures mapped to the color we see by our personal senses?
Color created by the sensor of my IR converted camera is called false color. I guess it could be called false temperature, too. I believe the sensor maps the intensity (energy level?) from the RGB elements of the direct and reflected electromagnetic radiation that is within its range. This is the reality of the Asperitas clouds in my images, not the color or temperature but the tone..
Wow, that was a long row to hoe. I hope I’m not confused or confusing somewhere in my explanation.
I photographed the Asperitas clouds with my IR converted camera, a Fujifilm X-T10 with an XC15-45mm F3.5-5.6 OIS PZ Fujifilm lens. The sensor type is CMOS II and the sensor format is APS-C. The effective pixels is 16 Mpx. The conversion filter over the sensor cuts off visible light smaller than 665nm wavelength. My IR conversion was done by lifepixel.com and they have a vast amount of information at their website.
