Polaroid ST-8E, ST-9E, ST-7E manual System Features

		Section 4 - Camera Hardware
	A/D	Temperature	Electromechanical	Electronic
Camera	Resolution	Regulation	Shutter/Shutter	Shutter
			Wheel/Vane
ST-5C	16 bits	Closed Loop	Shutter Wheel	0.01 second
ST-237	12 bits	Closed Loop	Shutter Wheel	0.01 second
STV	10+2 bits	Closed Loop	Shutter Wheel	0.001 second
ST-6	16 bits	Closed Loop	Vane	0.01 second
ST-7E/8E/9E	16 bits	Closed Loop	Shutter	None
		Table 4.2 - System Features

How these features affect the average user are discussed in the paragraphs below:

A/D Resolution - This is a rough indication of the camera's dynamic range. Higher precision A/D Converters are able to more finely resolve differences in light levels, or for larger CCDs with greater full well capacities, they are able to handle larger total charges with the same resolution.

Temperature Regulation - In an open loop system like the original ST-4 the CCD cooling is either turned on or turned off. While this provides for adequate cooling of the CCD, the CCD's temperature is not regulated which makes it important to take dark frames in close proximity to the associated light frame. Closed loop systems regulate the CCD's temperature to an accuracy of ±0.1° C making dark frames useful over longer periods.

Electromechanical Vane - Having the vane in the ST-6 means the host software can effectively "cover the telescope" and take dark frames remotely, without the user having to get up and physically cover the telescope.

Electromechanical Shutter - Having the shutter in the ST-7E/8E/9E gives streak-free readout and allows taking dark frames without having to cover the telescope. While the minimum exposure is 0.11 seconds, repeatability and area uniformity are excellent with SBIG's unique unidirectional shutter.

Shutter Wheel - The Shutter Wheel, used in conjunction with the camera's Electronic shutter, allows you to cover the CCD for taking dark frames and in the case of the ST-5C/237 allows replacement with a mini internal color filter wheel.

Electronic Shutter - Having an electronic shutter involves having a CCD with a frame transfer region. These CCDs actually have an array that has twice the number of rows advertised, where the bottom half is open to the light (referred to as the Image Area), and the top half is covered with a metalization layer (referred to as the Storage Area). In frame transfer CCDs at the end of the exposure, the pixel data from the Image Area is transferred into the Storage Area very rapidly where it can be read out with a minimum of streaking.

In addition to the system level differences between the various cameras, Table 4.3 below quantifies the differences between different CCDs used in the cameras:

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