sigma2

SIGMA2

The SIGMA2 is a compact astronomical ccd camera camera.

The SIGMA2 uses - as well as the SIGMA1 – KODAK ccd sensors. This ccd sensors offer high quality performance at affordable costs. A full 16 bit AD resolution, a 2 stage thermoelectric Peltier cooling and a fast USB computer interface is a matter of course.

Full frame or Interline ?

The design of the SIGMA2 makes it easy to use a lot of different ccd sensors. The well known full frame types can be used, as well as the some interline sensors and the new KAF8300 chip with 8,3 mega pixel.

Full frame sensors are characterized by its very high quantum efficiency (QE) up to nearly 90% and its low noise behavior. This is possible because the entire surface of each pixel can be used to collect light. In this case we talk about 100% fill factor. Interline sensors needs a portion of each pixel to store the collected charge during the readout process. The light collecting surface is reduced at this area and thus the qe is also reduced. Micro lenses on top of each pixel is a way to improve the sensitivity of the sensor up to 60% qe, but the high quantum efficiency of the full frame type cannot be reached.

Another important difference between full frame - and interline sensors is the full well capacity. It describes how many electrons can be stored in each pixel. The full well capacity of a interline sensor is significantly lower as of full frame sensors. This is a direct consequence of the reduced fill factor. As a first approximation it is save to say that the full well capacity of a interline sensor is 2 or 3 times lower as of a full frame sensor with same pixel geometry.

Unfortunately full frame sensors didn't only offer advantages. On of the main disadvantage is the behavior at over exposure. When the maximum capacity of a pixel is reached additional electrons tend to flow into adjacent pixels. This effect is known as blooming. This is what interlines sensors do not suffering on.

The SIGMA2 can be equipped with following ccd sensors:

Sensor	Typ	Pixel	Pixel	max. QE	Antiblooming

KAF1603ME	FULL Frame	1536 x 1024	9u	83%@580nm	No
KAF3200ME	FULL Frame	2148 x 1472	6,8u	87%@650nm	No
KAF6303E	FULL Frame	3072 x 2048	9u	65%@600nm	No
KAI2020	Interline	1600 x 1200	7,4u	55%@460nm	Yes
KAI4022	Interline	2048 x 2048	7,4u	55%@460nm	Yes
KAF8300	FULL Frame	3326 x 2504	5,4u	56%@550nm	Yes

Some differentccd sensors

The cooling stage

Semiconductors (a ccd sensor is also a semiconductor) creating thermal noise during operation. The higher its temperature of the sensor, the higher the noise in the image. An effective way to reduce thermal noise is to cool the sensors down as deep as possible. Thus, the SIGMA2 is equipped with a 2 stage thermoelectric Peltier cooler which is able to reach -40°C difference to ambient. The required temperature is precise controlled with an accuracy of +-0,1 C°. A precise controlled temperature is essentially for working with dark frame libraries. You better should use the clear sky for collecting photons instead of doing dark frames.

The ccd chip in the sigma2 is embedded in a air proofed chamber. The humidity inside the chamber is held below 5% with the help of a special desiccant. This prevent the sensor getting wet during cooling. If the desiccant is exhausted after some years of use, it can easily changed without opening the camera body.

The Shutter

Full frame sensors must be prevented for incident light during the readout process, otherwise you get an effect which is called smearing. For this reason the SIGMA2 is equipped with a mechanical shutter. The shutter type is a new designed “rotating shutter”. The advantage of this shutter type is to get uniform illuminated images – also with very short exposure times.

The SIGMA2 needs only a power connector and USB for the pc communication. Cables for both connectors are part of the shipment. The camera was designed to work with a single 12V supply. This can be a simple accumulator or a stabilized power supply for stationary use.

Beside the USB connector, some status LED`s are visible. It shows the status of the shutter, the camera itself and indicates possible errors.

Filter wheel needed ?

If desired, the SIGMA2 can be equipped with an internal 5 position filter wheel. The filter wheel can handle standard 1-1/4 inch color or narrow band filters. This option can be ordered for all sensor types except for the KAF6303. The wheel is controlled by USB bus.

Depending on whether the SIGMA2 is equipped with - or without a filter wheel, the max. thickness of the body is 68mm or 78mm.

Free Website Templates