CCD Readout Selection Guide (MV)

Spectroscopy:

S/N improvement can be made by evaluating the slit width and the seeing size when executing binning.

The binning size in spatial direction is estimated by 1/2~1/3 of the seeing size.

The binning size in slit direction is estimated by 1/2 of the slit size.

Partial readout mode is used for target acquisition, and it is necessary to take at least three exposures for the images (slit image, object image, image on the slit).

Notes

Overscan:

Overscan region is installed in every frame in order to dump the constant bias.
Overscan X size = 75 (For 1x1 bin）.
x=1~(overscan size) and Y=* are the overscan for chip1. (Overscan=[1:overscan,*])
x=(image X size)-(Overscan size) ~ (image X size) and Y=* are the overscan for chip 2. (Overscan=[image x size-overscan:image x size,*])
(Note that the overscan appears at different X positions for chip1 and chip2.)
The gap size between chips 1 and 2 is approximately 5 arcsec (49 pix) (Barely narrowed down from that in our previous SITe chips).This measures the distance from the last sensitive pixel in X on chip2 to the first sensitive pixel on chip1. In specific, it seems that effective pixels are lost due to the overscan installed on the gap between the chips, but there is no effective pixels lost since the overscan is read from the empty current with no electric charge flowing.

Actual read-out time:

CCD should be wiped for 3 seconds before every exposure. It will be a dead time when taking continuous scientific exposures, but in a lot of cases when the CCD wiping takes place at the same time as the slit is moving, no time is lost.
The following readout time is applied in each of the modes. The table indicates the actual time including the time spent for the data transfer and the FITS transfer added to the time spent for reading out the CCD. There is a slight difference in the readout time according to the computer loads, etc.
After change to Messia V system:
- Readout speeds got slower to reduce readout noise (8-10e- -> 4-5e).
- For some readout modes, fast readout can be used to speed up the read-out time.

Read Speed

Read Area

Binning
(xXy)

Readout
time (sec)

Image size
(spaceXdisp)

Overscan size
(x width)

e/ADU
(chip1, chip2)

Main Purpose

Normal
Whole
1X1
166
2047x4095
75
2.1 for imaging

Fast
Whole
1X1 130
2047x4095 75 4.05
for imaging
good for sky-limited noise conditions, (BB imaging, etc.)
for MOS pointing

Normal Whole
2x1
85
1023x4095
37
2.1 for spectroscopy

Normal Whole
3x1
61
683x4095
25
2.1 for spectroscopy

Normal Whole
4x1
49
512x4095
18
2.1 for spectroscopy

Normal Whole
2x2
52
1023x2047
37
2.1 for spectroscopy and imaging

Fast
Whole
2X2
42
1023x2047 37
4.05
for spectroscopy and imaging

Normal Whole
3x2
37
683x2047
25
2.1 for spectroscopy

Normal Whole
4x2
29
512x2047
18
2.1 for spectroscopy

Normal Whole
2x3
36
1023x1365
37
2.1 for spectroscopy

Normal Whole
3x3
26
683x1365
25
2.1 for spectroscopy

Normal Whole
4x3
20
512x1365
18
2.1 for spectroscopy

Normal Whole
3x4
19
683x1023
25
2.1
for spectroscopy

Normal Whole
4x4
15
512x1023
18
2.1 for spectroscopy

Normal Part
1X1
20
2047x199
75
2.1 for slit viewing (center slit)

Normal
Wide Part 1X1
27
2047x400 75 2.1 for slit viewing (center slit)
X2 wider FOV

Normal
Wide Part 2X2
15
2047x400 37
2.1 for slit viewing (center slit)
2X wider FOV
binned for maximum sensitivity for fainter targets

Normal Upper Part
1X1
30
2047x199
75
2.1 for slit viewing (offset slit)
(only for offset slits)

Normal
Wide Upper Part
1X1
36
2047x400 75 2.1 for slit viewing (offset slit)
2X wider FOV

Normal
Wide Upper Part
2X2
22
2047x400 37
2.1 for slit viewing (offset slit)
2X wider FOV
binned for maximum sensitivity for fainter targets

CCD Readout-Mode Selection Guide

Imaging:

Spectroscopy:

Notes

Overscan:

Actual read-out time:

Read Speed	Read Area	Binning (xXy)	Readout time (sec)	Image size (spaceXdisp)	Overscan size (x width)	e/ADU (chip1, chip2)	Main Purpose
Normal	Whole	1X1	166	2047x4095	75	2.1	for imaging
Fast	Whole	1X1	130	2047x4095	75	4.05	for imaging good for sky-limited noise conditions, (BB imaging, etc.) for MOS pointing
Normal	Whole	2x1	85	1023x4095	37	2.1	for spectroscopy
Normal	Whole	3x1	61	683x4095	25	2.1	for spectroscopy
Normal	Whole	4x1	49	512x4095	18	2.1	for spectroscopy
Normal	Whole	2x2	52	1023x2047	37	2.1	for spectroscopy and imaging
Fast	Whole	2X2	42	1023x2047	37	4.05	for spectroscopy and imaging
Normal	Whole	3x2	37	683x2047	25	2.1	for spectroscopy
Normal	Whole	4x2	29	512x2047	18	2.1	for spectroscopy
Normal	Whole	2x3	36	1023x1365	37	2.1	for spectroscopy
Normal	Whole	3x3	26	683x1365	25	2.1	for spectroscopy
Normal	Whole	4x3	20	512x1365	18	2.1	for spectroscopy
Normal	Whole	3x4	19	683x1023	25	2.1	for spectroscopy
Normal	Whole	4x4	15	512x1023	18	2.1	for spectroscopy

Normal	Part	1X1	20	2047x199	75	2.1	for slit viewing (center slit)
Normal	Wide Part	1X1	27	2047x400	75	2.1	for slit viewing (center slit) X2 wider FOV
Normal	Wide Part	2X2	15	2047x400	37	2.1	for slit viewing (center slit) 2X wider FOV binned for maximum sensitivity for fainter targets
Normal	Upper Part	1X1	30	2047x199	75	2.1	for slit viewing (offset slit) (only for offset slits)
Normal	Wide Upper Part	1X1	36	2047x400	75	2.1	for slit viewing (offset slit) 2X wider FOV
Normal	Wide Upper Part	2X2	22	2047x400	37	2.1	for slit viewing (offset slit) 2X wider FOV binned for maximum sensitivity for fainter targets