MODS Rainbow Logo

The Multi-Object Double Spectrographs
for the Large Binocular Telescope

[MODS1 and MODS2 on the LBT - 2014 April 9]
MODS1 and MODS2 (left and right) on the LBT - 2014 April 9

MODS1 and MODS2 are a pair of low- to medium-resolution Multi-Object Double CCD Spectrographs/Imagers designed and built by OSU for the twin 8.4-meter diameter mirror Large Binocular Telescope on Mt. Graham in southeastern Arizona. The two MODS are identical two-channel spectrographs, one for each of the direct f/15 Gregorian foci of the LBT, that can work in tandem on a single target to exploit the full 11.8-meter effective aperture of the twin LBT mirrors. They may also be configured individually for increased multiplex advantage (e.g., take spectra of twice as many targets in the same field), configured for complementary observations (e.g., MODS1 for red-only and MODS2 for blue-only when spectral features of interest might otherwise be lost to the dichroic cross-over wavelength region), or as half of a hybrid configuration with one MODS on one focal station working in parallel with the LUCI spectrograph on the other focal station to provide nearly continuous medium-resolution simultaneous spectral coverage from 0.32 to 2.5-microns. Parallel MODS+LBC configurations for joint imaging and spectrophotometric time-series work are also possible.

Each MODS is a seeing-limited spectrograph and imager working in the 320-1100nm wavelength range with a 6x6-arcminute field of view. Gratings provide a spectral resolution of R~2000 and double-pass prisms provide a low-resolution (R=500-150) faint-object mode. Multi-object spectroscopy is accomplished using laser-machined focal-plane slit masks fed into the beam from a 24-position mask cassette. A beam selector below the slit carries a dichroic that splits the incoming beam into separate red- and blue-optimized channels at a wavelength of 565nm. Each spectrograph channel has separately optimized collimators, dispersers, cameras, and detector, allowing simultaneous operation across the entire CCD band. The beam selector can also direct light into the red or blue channels alone, providing blue-/red-only modes to extend wavelength coverage into the dichroic cross-over for one channel. The MODS science detetors are 3Kx8K monolithic E2V CCDs; blue-coated standard silicon on the blue channel and extended-red coated 40-micron deep depletion silicon on the red channel.

MODS1 passed its laboratory acceptance review in April 2010 and was shipped to the LBT in May 2010 where it was reassembled and tested in the mountain instrument lab. It was successfully installed at the LBT left direct Gregorian focal station on 2010 August 31. After thorough technical and science commissioning from September 2010 through May 2011, MODS1 entered regular service for science observing in September 2011.

MODS2 was assembled and tested at OSU starting in 2011, and passed its laboratory acceptance review in August 2013. It was shipped to LBTO in October 2013 for re-assembly and testing, and installed on the LBT for the first time on 2014 April 9. Technical and science commissioning ran from 2014 until early 2015 when MODS2 became available for limited science operation.

Full binocular operation with both MODS was initiated at the start of 2016 in shared risk mode, and became the default observing mode in fall of 2016.

Instrument Characteristics

MODS Instrument Characteristics

CCD Detectors

Gratings and Prisms


Slit Masks

Estimated Performance

Detailed Optical Specification

Mechanical Systems

Information for Observers

User Manuals:
MODS Instrument Manual [v1.4, 2013 Jan 20 - 5Mb PDF]
MODS Observing Scripts Manual [v1.3, 2013 Jan 20 - 1Mb PDF]
MODS Basic CCD Reduction (modsCCDRed) [v2.0, 2019 Feb 2 - 3Mb PDF]
MODS Spectral Data Reduction Pipeline (modsIDL) [v1.0, 2019 Feb 20 - 4Mb PDF]

Observing Preparation Tools
modsTools - Observing Script Preparation [Updated: 2013 Jan 20]
modsView - Target Visualization & Guide-Star Selection [Updated: 2016 Oct 15]
MMS - Multi-Slit Mask Design Software [Updated: 2013 May 6]
Observing Planning Tools [Updated: 2012 Nov 6]
MODS1 Instrumental Sensitivity [Updated: 2013 May 16]

Instrument Calibration

Data Reduction Tools
Basic 2D CCD Reduction Package (modsCCDRed v2.0.4) [Updated: 2019 Feb 2]
modsIDL Spectral Data Reduction Pipeline (modsIDL v1.0) [Updated: 2019 Feb 20]

MODS1 at the LBT

Shipping, Re-Integration, & Commissioning: May 2010 to June 2011

[MODS1 Structure Moving Day - 2010 May 7]
MODS1 on the truck in Columbus ready to head to Arizona
2010 May 7
[MODS1 arrives on Mt. Graham - 2010 May 17]
MODS1 arrives on Mt. Graham
2010 May 17
[MODS1 lifted to the LBT LDG rotator - 2010 Aug 31]
MODS1 being lifted to the LBT left direct Gregorian focus
2010 Aug 31
[MODS1 on the LBT at last - 2010 Sept 1]
MODS1 installed on the LBT and powered up
2010 Sep 1
[MODS1 Image and Long-Slit Spectra of the Crab Nebula - 2010 Nov 19]
MODS1 Images and Long-Slit Spectra of the Crab Nebula
2010 Nov 19
[MODS1 MOS Spectrum of Abell 1689 - 2011 Mar 17]
MODS1 First Multi-Object Spectrum: Galaxy Cluster Abell 1689
2011 Mar 17

MODS2 at the LBT

Shipping, Re-Integration, & Commissioning: Oct 2013 thru Dec 2014

[MODS2 Structure Moving Day - 2013 Oct 1]
MODS2 on the truck in Columbus ready to be transported to Arizona
2013 Oct 1
[MODS2 at MGIO Basecamp - 2013 Oct 7]
MODS2 at MGIO Base Camp outside Safford, transloaded onto the observatory truck that will take it to up to the summit.
2013 Oct 7
[MODS2 Mountain Re-Integration - 2014 Jan 11]
MODS2 with all of its mechanisms re-integrated and the covers off in the LBT Mountain Lab
2014 Jan 11
[MODS2 Installation on the LBT - 2014 Apr 09]
MODS2 being mounted on the LBT right direct Gregorian focal station for the first time
2014 April 9

Design and Fabrication Images

Team MODS Progress Reports

External Project Reviews

Conceptual Design Review (1999 Mar 8-9)

Preliminary Design Review (2001 Sept 26)

LBTO Progress Review (2004 Apr 22-23)

Joint LBTO/TSIP Progress Review (2005 March 7-8)

Project Documents

Online Document Archive

Project Publications & Papers

MODS Project Personnel and Vendors

Team MODS:

[MODS1 and TeamMODS - 2010 Feb 15]
MODS1 and Team MODS in the Instrument Assembly Lab - 2010 Feb 10
Project PI:Richard Pogge
Project Scientists: Paul Martini and David Weinberg
Instrument Scientist: Bruce Atwood
Sr. Mechanical Engineer: Tom O'Brien
Optical Designers: Paul Byard (ret.), Ross Zhelem
Mechanical Engineer: Mark Derwent
Software Systems Developers/Engineers: Ray Gonzalez & Jerry Mason
Electronics Engineers: Dan Pappalardo & Mark Johnson
Design Engineer: S. Ralph Belville (ret.)
Senior Instrument Makers: Dave Brewer & Dave Steinbrecher
Electronics Technician: Ed Teiga, Brandyn Ward
Graduate Students: Jason Eastman, Jennifer Marshall, Rebecca Stoll
Student Engineering Assistants: Andy Krygier, Chris Colarosa, Justin Randles, Josh Rosenbeck

Our Sponsors:
The National Science Foundation NSF/NOAO TSIP Program

MODS is supported by the Ohio State University with major support provided by grants from National Science Foundation's Division of Astronomical Sciences Advanced Technologies and Instrumention (AST-9987045) and NSF/NOAO TSIP Programs, and with matching funds provided by the Ohio State University Office of Research and the Ohio Board of Regents. Graduate students have been supported by the David G. Price Fellowship in Astronomical Instrumentation.