LingueCapturing the image: Microlenses
When light enters a camera through the lens, it passes through the optics and eventually ends up at the sensor, where it is recorded. Contrary to popular belief, the sensor is not a mass of pixels that are all adjoined but is actually more like a mosaic of tiles with small gaps between each one where the circuitry is stored. If light falls into these gaps, it is not used to form any part of the image and is therefore effectively wasted.
Microlenses are an array of lenses laid over the top of the CMOS sensor that help to direct the light that reaches the sensor into each of the pixel (photodiode) wells. This arrangement ensures that all of the light that makes it into the camera body ends up in a pixel well and can therefore be used to form part of the image.
The EOS 50D DSLR introduced a development in the use of microlenses where the gaps between each lens were removed – this is known as ‘gapless microlenses’. This technology was further developed in both the EOS 5D Mark II and EOS 7D DSLRs with a reduction in the distance between the sensor and the gapless microlenses, thus giving low noise levels at all ISO settings and higher pixel sensitivity.
With the EOS-1D X DSLR, this gapless technology was used for the first time in a full-frame Canon sensor. The technology has also been included in the full-frame EOS 5D Mark III DSLR.
The advantage of using all the light that makes its way to the sensor is that the system is more efficient overall and less amplification is required in the processing circuitry – this leads to improved ISO performance, especially in low light level conditions where the light reaching each pixel can be very minimal.
A diagram showing the EOS 7D’s gapless microlenses (left) compared to the EOS 50D microlenses (right) – note that the distance between the sensor and the microlenses has been reduced. The reduced distance helps to give low noise levels at all ISO settings and higher pixel sensitivity.
