ISPI Overview

The Infrared Side Port Imager ISPI (eye-spy) is a facility infrared camera at the CTIO Blanco 4-m telescope, serving a broad range of science programs through the following capabilities:

1-2.4 micron imaging with 2K x 2K HgCdTe HAWAII-2 array
0.3 arcsec/pixel sampling matched to f/8 IR image quality of ~0.6 arcsec
10.25 x 10.25 arcmin field of view,
broad band J,H and Ks, as well as a set of narrow band filters.

ISPI is one component of a fixed instrument complement for future Blanco operations; the others are Prime Focus MOSAIC for optical imaging, and Hydra for multiobject optical spectroscopy. This fixed complement will lower operations costs on the Blanco as CTIO meets its committments for SOAR commissioning and operation, as well as Gemini operations support.

While ISPI's basic capabilities derive from its science mission, the project also faced realities of cost and schedule, space envelope at the 4-m Cass focus, and the future mix of instruments available to the community on the Blanco, SOAR, and Gemini South telescopes. The result is a conservative design which employs existing elements wherever possible (e.g. the optical design), uses a single large array, and has no spatial filtering (occulting masks) or spectroscopic capability. The ISPI project delivered a highly capable instrument quickly and at low cost. It complements future IR capability for high spatial resolution imaging and spectroscopy on SOAR and Gemini South, and a very-wide-field IR imager to be shared between the NOAO 4-m telescopes (NEWFIRM).

Block Diagram [1]

ISPI Filters [2]

ISPI Mechanical Design

ISPI is side-looking so that it may be mounted on the 4-m simultaneously with Hydra II. The space envelope is constrained by the mirror cell above and Hydra below. The refractive optical system is enclosed in a cylindrical, straight-through design with a strong heritage from the facility IR camera CIRIM. Liquid cryogens are used for instrument cooling.

The design separates into two dewars with separate cryogen tanks which surround the optical path. The fore dewar has the entrance window, collimator, and filter wheel assemblies. The aft dewar holds the camera and detector assemblies. The cylindrical construction provides a very stiff assembly to meet flexure requirements. The diameter is 14 inches and the total length of the dewar assembly is 45 inches, the weight for the complete assembly is expected to be ~220lbs.

The filter wheels provide 16 positions including darks and opens. There is a single fixed Lyot stop. Alignment to the telescope is accomplished by adjustments at the telescope interface.

March 22, 2004

ISPI Optical Design

The ISPI optical design originated with a design produced by Charles Harmer (NOAO) for the U. Florida IR camera FLAMINGOS [3]. This design was a close match to our science-defined specifications, was already optimized for the Mayall 4-m, and allowed cost savings by joint procurement of optics. Hence we adopted it for ISPI, with a slight reoptimization of element spacings for the Blanco telescope by Harmer and Maxime Boccas (CTIO).

This is a refractive, collimator-camera system with an intermediate cold pupil image. The f/3 camera employs one aspheric element; all other surfaces are spheres. Design performance is shown graphically below with spot diagrams (box size is 2x2pixels, ie. 36x36 microns)
The camera optics coupled to the Blanco 4-m give the following performance for 80% encircled energy diameter:

Band	Best in Field	Worst in Field	Spot Diagram
J	0.36"	0.48"	J Spot Diagram [4]
H	0.36"	0.48"	H Spot Diagram [5]
K	0.48"	0.55"	K Spot Diagram [6]

Note: The best and worst are not obtained respectively on axis and in the corner

The optics have been produced by Janos Technology, Inc [7]. The FLAMINGOS implementation has had first light [8] confimation of excellent image quality on Kitt Peak telescopes.

Ray Trace

ISPI Ray Trace

March 22, 2004

ISPI GUI

ISPI is operated through a Graphical User Interface, allowing the user to control the array and the filter mechanism. Through the GUI a limited set of telescope control functions is accessible, enabling the user to perform small off sets and to set the telescope focus. Telemetry of ISPI is also made available through the GUI. The ISPI GUI is an ARCview application, which allows the user to control both the instrument (array control & filter mechanisms) as well as some limited telescope , such as small off sets and telescope focus.

[9]

March 22, 2003

ISPI Performance

ISPI throughput

based on data taken on Dec. 21, 2004

Band	Background Flux (electrons/sec) per pixel	Integrated Flux (electrons/sec) for m=15 star
J	165	3000
H	1125	4565
K_short	1925	3085

The exposure calculator [10] on the CTIO Infrared Instrument web page [11] has been updated accordingly.

March 26, 2005