New Foveon Sensor, The Latest in Unconventional Sensor Design

PC Mag, Image Resource, DP Review and Pop Photo all have articles today on the new Sigma DP Quatro featuring a redesigned Foveon sensor.

 I suspect the timing has less to do with overwhelming interest and more to do with a news embargo timed to end today.  I have to admit, though, having four articles written on the same day is great for P.R.


How the Foveon Sensor Works

Conventional digital camera sensors utilize a single layer of photodetectors and a mosaic patterned filter.  The filter limits light hitting the detector to a specific color.  Different color are allowed through at different areas of the sensor.  These results are combined to produce a full-color image.

The Foveon sensor takes advantage of one of the properties of Silicon.  Light wavelengths (color) penetrate silicon to different depths.  Blue light only penetrates slightly with red penetrating the most.  The sensor uses three layers of photodetectors, each capturing light penetrating to different depths.

The depth is used to tell the camera what color is being captured.  The top level yields blue, the middle green and the bottom red.

(Technically, the top layer captures all light.  The middle all light except blue.  The bottom only captured red.  Determine blue/green requires a little extrapolation based on the light captured by the layer below.)

This design allows the sensor to capture all the light hitting the sensor instead of limiting the light to certain wavelengths.  The original generation of cameras using the technology did capture very detailed images, largely due to the ability to eliminate the color filter and low-pass filter used by typical camera sensors.  Unfortunately, they were also prone to noise at higher ISO settings.

The original sensor had three layers with equal resolutions.  This has been altered in the latest version so that the top layer has a much higher resolution than the lower two layers.  The top layer's resolution is four times that of the second and third layer.  (Top is 20MP, second and third 4.9MP each.)

Lowering the resolution of the bottom two layers may help lower image noise and increase processing speed.


Camera Design
The DP line comes in three fixed-lens versions.  The DP1 has a 19mm lens, the DP2 a 30mm lens and the DP3 uses a 45 mm lens.  (Equivalent to 28mm, 45mm and 75mm, or wide-angle, standard and minor telephoto.)

A large amount of the body has been eliminated. Viewing an image of the 30mm lens model emphasizes just how much of the body has been eliminated.  The lens extends above the camera body.

This is from the CNet review.  The published a day before the other sites.

The grip faces the opposite direction from what is used on most digital cameras and appears to have been angled slightly.  It almost looks as if Sigma decided to flip the typical body over, putting the lens on what originally was the back and the lcd on the front.

Prices have yet to be announced.