Fast CCD-photopolarimeter "x_CCD"

V.V.Korokhin

Camera. Photosensitive element of the system is CCD-matrix (CCD - Charge Coupled Device), installed in the serial camera OS-65D of company "Mintron". The camera was modernized so that frames frequency (25 Hz) falls in 2, 4 or 8 times. This allows back to scale up maximum time of accumulations of signal and, accordingly, threshold sensitivity of instrument. Moreover, this has reduced an information flow what has allowed to enter images into PC with relatively uncomplicated intercoupler.

Intercoupler. Intercoupler serves for the digitization of images from the camera and entering them in PC. High-precision high-speed analog-to-digital converter AD775 of company "Analog Devices" is applied. This ensures high photoelectric features of instrument. Scheme of double buffering digitized information and exchange by information with PC on interruptions is implemented too. This ensures an efficient functioning of the instrument in the multitasking operating systems. Parallel port, working in EPP mode (Enhanced Parallel Port) is used for connection with PC.

Controling program. Program "x_CCD" was developed to control registration and primary information processing. "x_CCD" is a part of the program complex (Beletskij et al, 1998). The program has graphic intuitive comprehensible, suitable user interface equipped by the help system that relieves training and using the program, especially in observation conditions. Let's describe main functions.
Registration:
1. Registration of frames series on PC disk.
2. Image outputting on the monitor in the real-time mode, for instance, for focusing.
3. Typing, viewing, editing accompanying information in the image file in FITS format.
4. Adjusting frame size, amounts of elementary frame in series, filename and other.
Primary processing:
1. Viewing a series of frames in the "cinema" mode.
2. Automatic correction of flat field and darkness signal of frames series.
3. Automatic combining semi-frames.
4. Automatic centering frames series.
5. Automatic centering and summation of frames series.

Main technical features:
1. Amount of elements (pixels) - 752(hor.) h 582(vert.).
2. Size of photosensitive sections (mm) - 4.9(hor.) h 3.7(vert.).
3. Amount of effectively used elements in vertical direction - 576.
4. Clocking modes (from the standard frames frequency) (see Table 1) - 1/2, 1/4, 1,8.
5. Flat field distortions - < 1%.
6. Signal/noise - 50 dB.
7. Camera does not require the cooling.
8. Type of the interface with PC - EPP (Enhanced Parallel Port).
9. Digitization of separate frame - 8 bits.
10. Rate of images entering is corresponding frames frequency (refer to. Table 1).

Parameter/Mode	1/2	1/4	1/8
Full frames frequency (Hz)	12.5	6.25	3.125
Semi-frames frequency (Hz)	25	12.5	6.25
Amount effectively used elements on horizontal direction (columns)	160	320	640
Time of semi-frame accumulations (exposure) minimum Tmin (ms)	0.2	0.4	0.8
Time of semi-frame accumulations (exposure) maximum Tmax (ms)	40	80	160
Minimum luminosity (lux)	0.05	0.025	0.0125