CMOS sensor trends and astrophotography, from amateur astronomers perspective

Nowadays, even in low light conditions, digital camera can quality pictures with higher ISO, noise and hot pixels have been gradually reduced.

Sony has introduced back illumination process for consumer market. Sony BSI sensors evolved  from Exmor to now Exmor RS( stacked) technology. This stacked technology allows further chip size reduction, which has strong demands in smartphone camera market.

Digital astrophotography is also benefited from such advances, utilising Back Side Illumination technology

Exmor:
Within the CMOS sensor, it outputs low-noise digital signals by "on-chip column AD conversion" and "dual noise reduction" to suppress noise in the first half of the process

In low light conditions, when a wide aperture is desirable to collect as much light as possible. At apertures wider than f/2.0, back-illuminated Exmor R sensors are significantly more efficient at collecting light than conventional, front-illuminated sensors. Back-illuminated sensors’ high tolerance for more oblique incident light angles also reduces the vignetting effect that some lenses produce around the edges of the frame. 

 Exmor R(back illuminated) has the advantage of higher light collecting efficiency, especially for incoming light angled at 10 degrees or more from optical axis, and for lens aperture of f/2.0 or larger.

but at the same time, pixel size is getting smaller to around 1 um(for mobile markets and surveillance)

So far digital camera were mostly using up to 5th gen Exmor R sensors.

The biggest sensors used in astro cams were mostly micro four thirds, APS-C, and just a few Full Frame size. Will these mean an slow end to digital astrophotography, which is asking for

• unprocessed RAW image output

•  low readout noise
•  high quantum efficiency
•  long > 100 seconds exposure ( for Deep Sky Objects)
•  big pixel size ( still relevant ? )
•  without colour filter array ( in narrow band Astrophotography)

Light pollution: 

At the same time, due to worsening light pollution around the world, human related air turbulence, narrow band imaging with monochrome sensors is used to fight against these conditions.

Most consumer market sensors are with colour filter array, monochrome type is often not an option, and such experts has to remove such by debayer process. But such retrofit could degrade or even damage the photodiodes just below the microlens layer and bayer layer. This process is both low yield and time consuming. All in all narrow band imaging is very promising, but need expensive narrow band filters same time.

above picture is cross section of NC81366W used in Nikon D4

In ten years time, it is hard to say, whether latest sensor advances , will still be in reach to amateur astronomers or not.

Those marked in red circle are used in astro cams. year on x-axis is year such sensor is used in DSLR. This is relatively  3 to 5 year behind DSLR market.


reference:
FRAMOS
chipworks

who's who in 2015 mobile camera market