As more types of modifications of webcams occured in the world I have decided to collect information from various SONY datasheets and place it into one place. The main goal is to compare the sensitivity of various chips and also create some comparison table with unified criteria - not all catalog measurements were done in the same conditions.
Original SONY CCD chip datasheets can be downloaded directly from SONY website.

According to SONY datasheets the sensitivity of CCD chip is defined as voltage of signal output at the center of screen when exactly defined light conditions are kept. The voltage value listed in datasheet is not directly measured value, but recalculated value from measured value for specific defined exposure time.
This sensitivity parameter tells nothing about signal to noise ratio of the output signal. Unfortunately S/N ratio of the chips is not defined in the datasheets. Also there are many other parameters which are important for overall image quality.

Before doing any conclusions from the following tables and graphs, please, read all the text carefully.
All tables and graphs are based on datasheets values with defined conditions.
The article doesn't tell, that CCD chip with the highest sensitivity value must be automatically the best choise for astro imaging.

The tables also include saturation parameter, which defines the upper limit of dynamic range.

1, Catalog parameters

The first table shows data in a form as it is provided by company datasheets:

⁽¹ Sensitivity measurement
The sensitivity of color CCD chips is measured for G (green) signal

⁽² Measurement conditions
Use a pattern box (luminance 706cd/m2, color temperature of 3200K halogen source) as a subject. (Pattern for evaluation is not applicable.) Use a testing standard lens with CM500S (t = 1.0mm) as an IR cut filter and image at F5.6 or F8. The luminous intensity to the sensor receiving surface at this point is defined as the standard sensitivity testing luminous intensity.
The value of signal is recalculated to nominal 1/30s exposure (i.e. if exposure during measurement was 1/100s, then the voltage value is multiplied by 100 and then divided by 30).

⁽³ Sensitivity measurement
The value of signal is recalculated to nominal 1/50s exposure (i.e. if exposure during measurement was 1/100s, then the voltage value is multiplied by 100 and then divided by 50).

As we can see, the chips were measured in the same light conditions, but color chips were measured with larger relative aperture (F5.6).

2, Parameters recalculated for the same objective lens (F8)

The next table shows the same data recalculated to the same measurement conditions - all with F8:

Note - sensitivity of ICX254AL, ICX255AL and ICX409AL chips was recalculated to 1/30s exposure.

Now we can see noticable higher sensitivity of B/W CCD chips.

3, Parameters recalculated to the same object pixel size

As ICX424 chips have larger pixel size, for the same object size (in pixels) higher focal length must be used. For the same scope (objective lens / primary mirror) it means, that bightness of object will be descreased (by the other words - the F ratio will be changed).

The next table compares sensitivities for the same object size:

⁽⁴ Sensitivity recalculation
Because of not square pixels, the sensitivity value was recalculated for getting the same pixel resolution in horizontal direction and even higher vertical resolution as it would be in case of 5.6µm x 5.6µm chip.

The following graph shows the chip sensitivities from the above table (the higher values are better):

As we can see, the most sensitive chip for the same object pixel size is ICX255AL chip used in surveillance cameras. In webcam category the most sensitive is ICX098BL.

4, Comparison table for exposure times needed for the same object brightness and pixel size

The following table compares exposure times of the chips for achieving the same object size and brightness.
As a base for comparison was selected ICX098AK chip and exposure time 100s.
The values are calculated according to typical sensitivity values (linear CCD characteristic is assumed).

Chip name	Type	Exposure time	The shorter times are better
ICX098AK	Color	100 s
ICX098BQ	Color	76 s
ICX098AL	B/W	39 s
ICX098BL	B/W	31 s
ICX424AQ	Color	102 s
ICX424AL	B/W	43 s
ICX255AL	B/W	24.5 s
ICX409AL	B/W	20.5s

4, Conclusion

The aim of the comparisons was to compare various chips for achieving the same image size and brightness.
Although ICX424 chips offer higher sensitivity catalog values than ICX098 line, for the same object size the longer exposures are required.
The most sensitive is ICX409AL chip. The only pitty is, that Astromeccanica's KC381 camera is not able to do long exposures (it's planetary camera).

However the image quality is affected not only by sensitivity, but also by signal to noise ratio, dark current and dark shading. The backgrounds from the newer SONY CCDs are very uniform, making small signals easier to pick out.

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Last Update: 14.09.2005