TRISPEC Readout Mode, Overhead, and Saturation Levels

Readout Mode and Overheads

The instrument has the only one readout mode what reads out a full area of frame, currently. The readout area and the overheads are the below table. The overheads include the time to readout and to write the data to disk. Since the array controller and program readout and write the data of three channels by turns (not simultaneously), 1 minitute (= 30 + 15 + 15 seconds) is required as the total overhead with a simultaneous exposure.
  Readout Area
Optical CCD 512 x 512 30
IR1 InSb 256 x 256 15
IR2 InSb 256 x 256 15

Minimum Exposure Times

The minimum exposure times of three channel are the below table. The minimum exposure time on the optical channel is limited by the shutter speed of the mechanical shutter. Although the mechanical shutter controls the exposure of the only optical channel, the shutter shuts out all light from telescope, since it is on the front of the window of the insturment. Since the shutter must be opened during simultaneous exposure, the exposure time on the optical channel must be longer than those of the infrared channels.
  Minimum Exposure Time
with Simultaneous exposure
Minimum Exposure Time
with Single exposure
Optical CCD 1.302 1.000
IR1 InSb 0.302 0.302
IR2 InSb 0.302 0.092

Saturation Levels

The saturation levels of three arrays are the below table. However, unfortunately, we have been not able to measure them and linearity accurately yet (especially for the infrared arrays). Please notice that they have some uncertianess. For safety, the count should be remained under 80% of  the saturation level on the infrared channels.
  Saturation Level
Optical CCD 60000
IR1 InSb 10000 (*)
IR2 InSb 10000 (*)
(*) 8000ADU is safe

[Z-lab Home Page] [TRISPEC Top Page]

Last Modification Date: 2001/03/27
Last Modification Author: Makoto Watanabe <>