Shutter speed

---

Theoretically speaking shutter speed has no impact on image colour however there are a number of side effects that can affect colour under certain circumstances.

• Lighting colour temperature shifts. This occur with most AC (alternating current) lights and is typically worst with fluorescent tube lighting which swings wildly between green and magenta at 50 or 60Hz. Short shutter speeds can catch the light in one of these green or magenta phases. The only solution is to use longer shutter speeds that include at least one cycle.

• Noise. Long exposures are usually subject to some degree of thermal noise, whereby infrared (heat) energy affects the signal. One problem caused by heat is amp glow which tends to result in a red/purple cast in one corner. In addition very short shutter speeds capture very little light, producing a weak signal on the sensor which needs to be amplified yielding a poor signal to noise ratio. Again this affects colour channels differently with a lot more noise in the blue channel, resulting in a slight shift in the shadows toward blue.

Aperture

---

All of the low light noise effects also apply to narrow apertures (e.g. f/16). In addition to this are affects specific to aperture:

• Axial colour. Lenses with large maximum aperture (e.g. f/1.4) commonly exhibit longitudinal chromatic aberration, otherwise known as axial colour, which causes out of focus details in front of the plane of focus to be tinted green, and out of focus details behind the plane of focus to be tinted magenta.

• Contrast. Fast lenses also exhibit low contrast wide open due to various aberrations, the overall effect of which is to reduce colour intensity.

• Purple fringing. There are many explanations of this effect, which leaves a strong blue/purple glow around high contrast edges. The best I've heard is that it is chromatic aberration in the infrared spectrum. Again this tends to happen when the lens aperture is wide open.