Filter Wheels

Table 3.8: Filter Wheel Specifications

Drawing:	RCT001/6
EOS Drawing:	SCH-4025-1
Sketches:	MM 10-3
Motor:	d.c. servo with 25:1 reduction
Motor Encoder:	Scale: 1183.033 for FW1
	Scale: 1182.261 for FW2
Rotation:	Positive is left as viewed through access port.
Overall Encoder:	1000 lines per rev. giving 1 arcminute
Limits:	none (although SCH 4028-1:3 shows limits)
FW1 Controller:	PMAC#12
FW2 Controller:	PMAC#13
FW1 Drive Amplifier:	Amp 9
FW2 Drive Amplifer:	Amp 10
Homing:	one per wheel connected to the HomeFlag
Notes:	FW1
Positions per wheel:	9 (1,2,3,4,5,6,7,8,9)
Max Speed:	10 degrees per second 5 deg/sec/sec acc.
Filter Size:	4.5 inch
Thickness:	2-10 mm

Note: The schematic show "detents", these notches are closed when the filter is in position. They are connected to the +LIM.

There is a large set of filters available at the RCT. Each is a round filter close to 4.5 inches in diameter with widths ranging between 2 and 10mm. There is a set of broadband filters approximating the Johnson set and its extensions. Most of these are of the "colored glass" type. The broadband I filter, however, is an interference device. There is a larger set of narrowband interference filters centered on various nebular emission lines and off-line regions that will contain continuum emission.

The filters fit into large wheels located in the combined filter/guide camera box on the back of the telescope. Each wheel has 9 openings, with one slot (no. 9) left open on each filter wheel. This way, one filter is positioned in the beam along with an open slot on the other wheel. The filter slots are printed on the wheels with each number (1-9) stamped on the edge of the wheel directly opposite from the slot. The filter wheels rotate in both directions, either through a gentle push by hand or when commanded by the observatory software. The filters lock into position where a detent grabs onto notches on the side of the wheels.

The broadband filters, which are used extensively, are all located in filter wheel 1. Many of the narrowband filters are put in filter wheel 2, which is the wheel most easily removed from the telescope. A third filter wheel is available for storing a separate set of filters off the telescope. This wheel can be swapped with wheel 2.

Below are the current filter assignments to wheels 1 and 2. Some filters are kept in storage along with empty wooden filter boxes for the filters on the telescope. These filter boxes are kept in storage cabinets in the dome or control room.

[Filter Wheel 1]

Table 3.9: Current Filter Wheel Assignments

Position	Filter
1	U
2	V
3	B
4	R
5	I
6	I+
7	$H_{\alpha}$ Narrow
8	[NII] 6585
9	open

[Filter Wheel 2]

Position	Filter
1	Red Continuum
2	[SII] 6731
3	[SII] 6716
4	[NII] 5759
5	Green Continuum #2
6	[0III] 5007
7	$H_{\beta}$
8	Hel 4689
9	open

Table 3.10: There is a single numbering scheme also used to specify the filters. It ranges from 0 to 16 inclusive.

Numbering
#	FW1	FW2
0	9	9
1	9	1
2	9	2
3	9	3
4	9	4
5	9	5
6	9	6
7	9	7
8	9	8
9	1	9
10	2	9
11	3	9
12	4	9
13	5	9
14	6	9
15	7	9
16	8	9

Table 3.11: Filter Data

Filter Name	Header Value	Andover Part #	Central Wavelength (Å)	Width (Å)	Trans. plot$^1$
U	u	ANDV8303			U.gif
B	b	ANDV8666	4248	964	B.gif
V	v	ANDV8667			V.gif / Valt.gif
R	r	?			R.gif
I	i	ANDV8669	8105	1674	I.gif
I+	?	ANDV8307??			Iplus.gif
HeI4686	4686a/heii	ANDV8163	4689	29	HeI4686.gif
green continuum #1	?	ANDV8164	4807	47	gr_cont1.gif
$H_{\beta}$	4861a/hbeta	ANDV8165	4865	29	Hbeta.gif
$[OIII]$ 5007	5007a/$[oiii]$	ANDV8166	5008	25	OIII5007.gif
green continuum #2	5300a/green _continuum _#2	ANDV8167	5312	90	gr_cont2.gif
$[NII]$ 5755	5755a/$[nii]$	ANDV8168	5759	29	NII5755.gif
red continuum	6450a/red _continuum	ANDV8169	6458	80	rd_cont.gif
H$_{\alpha}$ (wide)	?	ANDV8282	6564	17	Halpha_wide.gif
H$_{\alpha}$ (narrow)	6563a/halpha _1nm	ANDV8281	6565	9	Halpha_narrow.gif
$[NII]$ 6584	6584a/$[nii]$	ANDV8283	6585	10	NII6584.gif
$[SII]$ 6717	6717a/$[sii]$	ANDV8284	6716	9	SII6717.gif
$[SII]$ 6731	6731a/$[sii]$	ANDV8285	6729	8	SII6731.gif

$^1$ See Appendix