For film, there are not really dedicated infra red cameras. Often lenses have different focus distance markings due to the differences in diffraction through glass between infrared frequencies and visible frequencies.

With digital, there are two ways of modifying cameras for infrared. Both involve removing the band pass filter (also called the “hot mirror”) from in front of the the sensor.

This makes the sensor “full spectrum.” In addition to visible frequencies sensors also respond to frequencies in the infrared and UV adjacent to the visible spectrum.

Once the sensor is full spectrum, Infrared photography can be done by placing high pass infrared filters in front of the lens before making the photo. There are IR screw in filters available for most common lens thread diameters.

Alternatively, the hot mirror can be replaced with an infrared high pass filter directly in front of the sensor. Then there is no need for screw on IR filters for the lens.

The downside of placing the IR filter at the sensor is inflexibility. The modified camera has a hard limit to the frequencies it will capture. If you know what frequencies you want, then that’s less of a potential concern.

The tradeoff for leaving the camera full spectrum is that screw on filters are always required in the size of any lens you want to use. And that is multiplied by the number of frequencies at which you want to filter.

For starting out, the big unknown is which frequencies work best for you. The easier way is a range of high pass filters that screw onto a lens. Once you know, then a camera with an internal IR filter might be desirable.