CTIO 5.75X5.75-inch Filters

A. Walker 18 Dec 2002

The Mosaic II imager, used at the Blanco 4-m prime focus, takes filters that are 146x146mm and 12mm (nominal) thick.

Focus offsets are referred to the R filter, since this is the filter we use for taking focus frames each night when the Mosaic is installed in order to monitor telescope performance.

We are (slowly) measuring these filters, let us know if there is any one you particular want to have us scan. Note that the Sloan set (griz) and the Johnson-Cousins BVR (but not I) sets should be near-identical to those at KPNO, see the KPNO Mosaic Filters. [1]

A set of standardized filter names and IDs have been developed to ensure proper application of astrometric solutions and real-time display processing (as well as future archive uniformity). These official names are listed in the Mosaic filter list [2]web page.

Filter	Center wavelegth	fwhm	focus offset microns	NOAO code	Status

U	3570	650	-185	c6001	OK
B	4360	990	+10	c6002	OK
V	5370	940	+30	c6026	from 21 OCT 2000
R	6440	1510	0	c6004	OK ... filter offset ref
I	8050	1500	+10	c6028	from 24 May 2003

VR Stubbs aka VR Supermacho	6100	2000	0	c6027	transmission curve [3]

C (Wash)	4000	1000	+260	c6006	OK
M (Wash)	5020	1020	+260	c6007	OK
D51 (DDO)	5130	154	-55	c6008	OK

[OII]	3727*	50	?	c3012	not tested yet
[OIII]	4990*	60	+130	c6014	OK
Halpha	6563*	80	+65	c6009	cwl, fwhm nominal
Halpha+8	6650*	80	-35	c6011	cwl, fwhm nominal
[SII]	6725*	80	+60	c6013	cwl, fwhm nominal

u (SDSS)	3600	400	+230	c6021	cwl, fwhm approx, Red Leak! [4]
g (SDSS)	4813	1537	+30	c6017	"set #2" (in use 8/2000-)
r (SDSS)	6287	1468	+120	c6018	"set #2" in use 8/2000-)
i (SDSS)	7732	1548	-20	c6019	"set #2" (in use 8/2000-)
z (SDSS)	9400	2000	-15	c6020	OK

Bj (Tyson)	4350	1650	?	c6024	#3, on loan from A. Tyson
I (Tyson)	8800	2000	?	c6025	cwl, fwhm approx

White	6500	5000	?	c6016	just a piece of fused silica


Retired Filters
g (SDSS)	4825	1380	?	c6015	"set #3", red cut-off a bit too red (in use <8/2000)
V	5370	940	115	c6003	small chip in corner, in use <10/2000
Bj	4350	1650	?	--	broken...
Bj	4350	1650	?	--	broken...
I	8050	1500	+25	c6005	Filter damaged Nov 2002- The are civered by CCD-1 (SW corner) is unusable

* = NOTE that the central wavelength of narrow band filters (actually all filters, but it is only significant for narrow band filters) is shifted aprox. 15A to the BLUE in the f/2.87 beam of the Blanco 4m + PFADC corrector as compared to the transmission measured in parallel light. The central wavelengths quoted above are nominally for when the filters are used at PF, with the aprox. 15A shift included.

Last updated: 2003 June 4 by C.Smith

Staff Contacts:
Alistair Walker: awalkerATnoao.edu
Chris Smith: csmithATnoao.edu

u leak

Subject: There is a leak -- just how much does it matter -- your call
Date: Fri, 8 Mar 2002 16:25:43 -0700 (MST)
From: Buell Jannuzi

Hi Guys,

Well there is a red leak in the ctio SDSS u' filter -- at a very low level, but perhaps enough to explain the flat field counts Mauro reports -- I'm afraid I have not had time to think this through carefully. Below are attached the asci data files containing the traces (done in the center of the filter) made by Jim DeVeny. The good news is that in the band-pass the ctio SDSS u' filter is a good match to the tracing I have on file for the actual SDSS u' filter (measured in air -- not in vacuum as actually used). The bad news is that while the SDSS u' does not appear to have a red leak (actual measurements of that filter between 8100 and 1100 angstroms so nothing), apparently because in addition to the 1mm UG11 + 1mm BG38 there is a film to, and now I'm quoting the message I got in 1996 about this filter, "suppresses a strong leak around 7000 Angstroms and acts as an AR coating in the passband. Now, the ctio SDSS u' filter does not have strong leak at 7000 -- but does have a leak near H-alpha (0.04%, tiny), with an increasing leak longward of 8000, but again, not huge -- but very significantly different from the SDSS filter.

As I said, I'm not 100% sure the measured leak accounts for Mauro's measured count difference in the flats he took last night -- but given the tracing I'm hard pressed to understand how the ctio SDSS u' filter could yield more counts than the Harris U without there being a significant leak (one might have hoped that the poor red response of the CCDs might have helped, but it looks like they are hot enough in the red to see some of the leaked light).

Buell

Attached files:

ctioSDSSu_leak.gif [5]
ctioSDSSu.gif [6] --- the SDSS u', the ctio SDSS u', and the KPNO Harris CuSO4 U
ctiosdssu.dat [7] --- asci data file from the tracing done in the band pass by J. DeVeny
ctiosdssuleak.dat [8] --- asci data file from the tracing done over broader wavelength range, by DeVeny

Note that the two data files will differ ever so slightly in the region covered by both tracings, but the slit used was 5 times larger (lower res) in the second set up.