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Guide to FOCAS imaging exposure times
Background-limited operation
With a read noise of 8-10 e- rms, FOCAS achieves
background-limited performance (BLIP) when the background level
reaches ~300 e-, as indicated by the following table.
Filter | Background |
Min. BLIP time (s) |
(mag/arcsec2) | e-/s/pixel |
---|
U | 21.3 | 0.6 | 500 |
B | 21.9 | 4.0 | 80 |
V | 21.1 | 7.6 | 40 |
R | 20.5 | 12.0 | 25 |
I | 19.5 | 22.9 | 13 |
Note: these background levels are for dark time. BLIP times
will be significantly reduced at other lunar phases.
Saturation magnitudes
The following table lists the point source saturation magnitudes in
good (0.3'') seeing for a number of different exposure times.
Filter | Saturation magnitude |
Maximum exposure (s) |
1 s | 10 s | 60 s | 300 s | 900 s |
---|
U |
11.9 | 14.4 | 16.4 | 18.1 | 19.3 |
52 000 |
B |
14.6 | 17.1 | 19.1 | 20.9 | 22.1 |
7 500 |
V |
14.5 | 17.0 | 19.0 | 20.8 | 22.2 |
4 000 |
R |
14.4 | 16.9 | 18.9 | 20.8 | 22.2 |
2 500 |
I |
14.1 | 16.6 | 18.6 | 20.6 | 22.8 |
1 300 |
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