WFC overheads

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WFC overheads

Readout and cycle times
Filter changes
Telescope slewing
Guide star acquisition
Guide star tweak
Overlapping tasks

Readout and cycle times

The cycle time is the time taken to complete a single observation of the minimum exposure time (0 seconds) including all the overheads. The time is measured from submitting the command until it returns to the command prompt. This time varies by about +- 1.5 seconds from the average value given in the table below.

Binning	Readout Fast mode	Single Cycle (old)	Single Cycle (new)
	Time (s)
1x1	34	42	39.93
2x2	15	--	16.98
3x3	--	--	10.13
4x4	--	--	6.832

NOTE: The new SDSU code with binning has not yet been commisioned.

Filter changes

The table shows the time (in seconds) needed to change the filters in the filter wheels. The filter wheel has 6 positions and can move in both directions. The times are measured using commands like time filter U noting how many positions the filter wheel has to move.

	Filter position offset
	1	2	3
Time (s)	5.70	7.12	9.82

A much larger contribution to the filter change time may come from the adjustment of the telescope focus to compensate for the difference in filter thickness. The following table gives the times until the focus drive has settled after a filter change.

Focus adjustment time [s]

Filter ID	To ->	191	192	193	194	195	196	197	198	199	200	201	204	206	207	210	211	212	214	215	220	222
From v	Filter Name	B	V	R	I	Z	O3	Ha	stU	stV	stB	stY	U	HE2	O2	KPB	O3r	SII	r	i	g	CLR
191	Harris B	--	0	0	0	14	50	46	61	58	58	58	46	24	37	39	54	59	20	27	37	45
192	Harris V	0	--	0	0	14	50	46	61	58	58	58	46	24	37	39	54	59	20	27	37	45
193	Harris R	0	0	--	0	14	50	46	61	58	58	58	46	24	37	39	54	59	20	27	37	45
194	INT-WFC I	0	0	0	--	14	50	46	61	58	58	58	46	24	37	39	54	59	20	27	37	45
195	Gunn z	14	14	14	14	--	49	45	60	57	57	57	45	22	34	38	53	58	17	24	34	46
196	[OIII]5007	50	50	50	50	49	--	22	38	33	33	33	21	45	40	38	24	35	47	44	40	68
197	Halpha	46	46	46	46	45	22	--	42	39	39	39	13	41	34	29	34	40	43	40	34	64
198	stromgren u	61	61	61	61	60	38	42	--	19	19	19	42	56	51	49	28	17	58	55	51	79
199	stromgren v	58	58	58	58	57	33	39	19	--	0	0	39	53	48	46	21	15	55	52	48	76
200	stromgren b	58	58	58	58	57	33	39	19	0	--	0	39	53	48	46	21	15	55	52	48	76
201	stromgren y	58	58	58	58	57	33	39	19	0	0	--	39	53	48	46	21	15	55	52	48	76
204	RGO U	46	46	46	46	45	21	13	42	39	39	39	--	41	34	30	33	40	43	40	34	64
206	HeII4686	24	24	24	24	22	45	41	56	53	53	53	41	--	24	30	49	54	17	14	24	50
207	[OII]3727	37	37	37	37	34	40	34	51	48	48	48	34	24	--	17	44	49	30	22	0	55
210	Kitt_Peak B	39	39	39	39	38	38	29	49	46	46	46	30	30	17	--	42	47	34	27	17	57
211	redshifted [OIII]	54	54	54	54	53	24	34	28	21	21	21	33	49	44	42	--	24	51	48	44	72
212	[SII]6725	59	59	59	59	58	35	40	17	15	15	15	40	54	49	47	24	--	56	53	49	77
214	Sloan r	20	20	20	20	17	47	43	58	55	55	55	43	17	30	34	51	56	--	20	30	48
215	Sloan i	27	27	27	27	24	44	40	55	52	52	52	40	14	22	27	48	53	20	--	22	51
220	Sloan g	37	37	37	37	34	40	34	51	48	48	48	34	24	0	17	44	49	30	22	--	55
222	Clear	45	45	45	45	46	68	64	79	76	76	76	64	50	55	57	72	77	48	51	55	--

The time for a filter change is the maximum of the filter change time and the focus drive adjustment time.

Telescope slewing

Sorry, no information yet.

Guide star acquisition

Sorry, no information yet.

Guide star tweak

Sorry, no information yet.

Overlapping tasks

The following tasks can savely be done while an exposure is being read out without producing additional noise on the images:

Slewing the telescope to a new target
Filter wheel movement

Back to WFC Homepage

Last Updated: 29 October 2002
Robert Greimel greimel@ing.iac.es