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FILTERSFILTERS FORFOR ASTRASTRONOMYONOMY & AEROSPACE

Bringing Information to Filters for and Aerospace

Introduction a wide variety of bandwidths with highly

MEGA OPTICAL designs and controlled cut-on and cut-off edge slope. manufactures custom filters Available scientific can be com- O and standard prescription filters bined to match existing requirements or to to the highest imaging quality standards define novel filters. We continue to offer for , atmospheric scientists, the highest finesse Fabry-Perot interference and aerospace instrumentation companies filters using both metal and dielectric worldwide. Applications include both reflectors. terrestrial and space-based observational instruments. We have supplied projects and Custom Filters programs for a wide variety of prestigious Many astronomy imaging applications Glowing in the universities, , government require the custom design and manufacture like a giant eye, the plane- agencies, and international consortia. As of filters and filter sets. With more than tary NGC 6751 is a cloud instrument technologies and applications twenty vacuum deposition systems—includ- of gas ejected several thousand evolve, we work collaboratively with ing IAD, electron beam, plasma enhanced, years ago from the hot visible customers to develop solutions for the and multi- coating technologies—we spectral, optical, and environmental are able to produce filters of extreme uni- in its center. Images are taken demands that will define observational formity and precision in quantities of one to through different filters, including astronomy and aerospace applications one thousand according to the following Omega filter F555W, in order to in the future. general specifications: isolate nebular gases of different I Range: UV to mid IR temperatures. The images are Large Format Filters I Bandwidths: 0.15nm to several hundred nm I then digitally combined and As observational instruments and detectors Tolerances: Critical throughput, band- increase in sensitivity and size, we con- shape and bandwidth requirements pseudo-colored. Image courtesy tinue to support the needs of the - I Sets: Matching physical and optical of NASA’s Jet Propulsion omy community through development of performance attributes Laboratory. capabilities to produce filters with apertures I Materials: Space-flight compatible as large as 210mm. These filters are well matched for manufacture using Omega’s proprietary ALPHA™ Technology, producing Capabilities and Features temperature, and imaging quality. Contin- uum filter sets are made with precise High Spectral Performance matching of the cut-on and cut-off wave- We provide interference passband filters lengths of spectrally adjacent filters. Space- with peak located from the UV based application filters are manufactured to the mid-IR and with bandwidths ranging using “space-flight compatible” materials. from 0.15nm to several hundred nanometers wide. Our filters meet demanding through- Photometric Filter Sets put and bandshape requirements while We produce a variety of photometric filter adhering to very close tolerances on band- sets (often called “UBVRI”) that isolate width and peak transmission wavelength. broad areas of the spectrum. These filters Many of our filters are designed for high are made by combining a number of filter attenuation of adjacent emission lines. glasses and/or dielectric spectral control Our coating processes assure uniformity of films. They are useful for both imaging spectral performance over the physical area and photometric classification. We produce of large filters. many sets with modified designs to achieve Previously unseen details of a required performance, such as accommo- High Optical Performance mysterious, complex structure dating the spectral response of detectors Our filters are made to rigorous imaging or maximizing peak energy. within the , one of requirements. We start by polishing optical the outstanding features of the glasses to requisite flatness and wedge Narrow-Band Filters Southern-Hemisphere portion of the values prior to coating and assembly. By Our narrow-band filters are highly effective , as revealed by NASA’s designing each coating for the longest free at isolating monochromatic emission and spectral range, we minimize the number of Hubble Space image of absorption lines, featuring high throughput, laminations that cause internal reflection the “Keyhole Nebula.” The picture deep out-of-band attenuation, and close and fringe patterns. After assembly, our control of spectral location. The perform- is a montage assembled from four filters are polished to achieve minimum ance of narrow-band filters is critically telescope pointings with Hubble’s wavefront distortion. Our Broadband dependent upon system speed and operat- Wide Field Planetary Camera 2, Achromatic Twyman- interferometer ing temperature. Much care and attention is enables us to evaluate transmitted wave- using six color filters, including given to the design, manufacture, and front at the filter’s principal wavelength. Omega Optical’s F439W, F555W, measurement of these filters to assure that Durable anti-reflective coatings are peak performance is reached at the desig- and F814W. Image courtesy of deposited on outer surfaces to increase nated system and operating environment. NASA’s Jet Propulsion Laboratory. transmission and reduce ghosting.

Physical Attributes

Many of our astronomy filters are made in sets or as supplements to existing sets. Each filter is designed to match the others in attributes such as optical thickness, bandshape, throughput, attenuation, sensi- tivity to system ratio, sensitivity to Bessell Sets

UR STOCK Bessell Photometric anti-reflective coated. Each filter’s spectral Sets, manufactured to the defini- response is determined by the combined O tion put forth by M. Bessell, offer responses of Schott filter glasses polished N 49 is a remnant high optical quality suitable for demanding to prescription thicknesses. The individual within the Large Magellanic imaging requirements. Filters are polished glasses are then laminated into a single- to stringent transmitted wavefront, wedge, piece optical assembly. The result is a set Cloud, a nearby, small companion and flatness specifications and are then of precision filters at an economical price. to the Milky Way, visible from the Southern Hemisphere. 100

The Hubble Heritage image of 90

N 49 is a color representation of 80 data taken with Hubble’s Wide 70 Field Planetary Camera 2. Omega 60 filters F814W (I) and F547M were R I 50 used to sample light emitted by U B V 40 sulfur ([S II]), oxygen ([O III]), and % Transmission (H-alpha). Image 30 courtesy of NASA’s Jet 20

Propulsion Laboratory. 10

0 300 400 500 600 700 800 900 1000 1100 Wavelength (nm) Figure 1: Bessell Photometric Set Spectral curves of Bessel U, B, V, R, I filters.

Imaging Enhancement Attributes I Transmitted Wavefront Distortion: λ/4 (or better) per inch. I Anti-Reflective Coating: multi-layer dielectric AR coating I Wedge: Less than 30 arc seconds. on both surfaces. R typically <0.5% to increase transmis- sion and reduce ghosting. I Flatness: λ/4 (or better) per inch. I Anti-Reflective Coating Durability: to moderate abrasion I Surface Quality: E/E as defined by Mil-C-48497A. as defined by Mil-C-48497A.

Filter U Filter B Filter V Filter R Filter I Complete Set 1.0 mm of UG 1 2.0 mm of GG 385 2.0 mm of GG 495 2.0 mm of OG 570 2.0 mm of WG 305 (Filters U–I) 1.0 mm of S-8612 2.0 mm of S-8612 3.0 mm of S-8612 3.0 mm of KG 3 3.0 mm of RG 9 3.0 mm of WG 305 1.0 mm of BG 12 Formats Part #: XBSSL/U Part #: XBSSL/B Part #: XBSSL/V Part #: XBSSL/R Part #: XBSSL/I Part #: XBSSL 25mm Round $100 $100 $100 $100 $100 $400 25mm Square $100 $100 $100 $100 $100 $400 28mm Round $125 $125 $125 $125 $125 $500 32mm Round $125 $125 $125 $125 $125 $500 38mm Round $150 $150 $150 $150 $150 $600 50mm Round $250 $250 $250 $250 $250 $900 50mm Square $250 $250 $250 $250 $250 $900 SBIG† $175 $175 $175 $175 $175 $600

Note: Spectrophotometric curve(s) are provided for each filter or set. Instructions for handling and cleaning surface-coated optics are provided for each filter or set.

† Mounted in 1 1/ 8 in. eyepiece, compatible with SBIG filter wheel. Prices listed are U.S. domestic prices. Duties, fees, and taxes required for international sales are additional. Hubble

MEGA OPTICAL has supplied filters and environmental specifications of the for the ’s mission, and have been used to produce O Wide Field and Planetary Cam- countless images of , nebula, and eras WFPC2 and WFPC3, which have been other astronomical features. Omega pro- in service since 1993. These filters were vided five Broad Band and six Medium designed to meet the stringent optical Band filters for the WFPC2.

100

90

80

70 439W 606W 60

50 Hubble image of a giant star-

40 forming region in the southern

% Transmission 380W 622W 814W 30 sky known as the Carina Nebula

20 (NGC 3372), combining the light

10 from three different filters tracing

0 emission from oxygen (), 300 400 500 600 700 800 900 1000 1100 hydrogen (green), and sulfur Wavelength (nm)

Figure 2: Wide Field and Planetary Camera (WFPC2) Broad Band Filters (). The color is also represen- Spectral profiles in Figure 2 are actual measured curves of filters installed and operational on WFPC2 tative of the temperature in the since 1993. ionized gas: blue is relatively hot

and red is cooler. Omega Optical 100 filters F439W, F555W, and F814W 90 were used to make this image. 555 80 675 Image courtesy of NASA’s Jet 70 Propulsion Laboratory. 60

50

40 % Transmission

410 547 791 30

20 467 10

0 300 400 500 600 700 800 900 1000 1100 Wavelength (nm)

Figure 3: Wide Field and Planetary Camera (WFPC2) Medium Band Filters Spectral profiles in Figure 3 are actual measured curves of filters installed and operational on WFPC2 since 1993. The panoramic picture at right is part of a 360° view comprised of 243 images taken by ’s panoramic camera over several

Martian days (sols) during the

Thanksgiving holiday, 2004 near

Husband Hill. It is an approxi- mate true-color rendering Exploration Rovers generated from images taken MEGA OPTICAL provided all filters for (Pancam) is a camera equipped with through Omega Optical’s 750, the two Mars Exploration Rovers eight filters per detector which provides (MER), Spirit and , high-resolution, multispectral panoramic 530, and 480nm filters. Photo O launched in 2003. Working with NASA Jet images of the Martian landscape. The filters courtesy of NASA/JPL/Cornell. Propulsion Lab and Cornell University, include those for geological investigation as Omega manufactured filters which serve as well as imaging. The Rover is also components of each MER’s three equipped with two Navigation Cameras (Nav- camera systems, utilized for scientific imag- cams) and four Hazard Avoidance Cameras ing and navigation. The Panoramic Camera (Hazcams), all of which use Omega filters.

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70 L6 L5 R4 60 R5 50 R6 40 R7 30 L7 L4 L3 R3

% Transmission 20

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0 300 400 500 600 700 800 900 1000 1100 Wavelength (nm) Figure 4: Panoramic Camera Filters Spectral profiles are actual measured filters from Rovers Spirit and Opportunity, which have been imaging the Martian surface since 2004.

λeff Bandpass λeff Bandpass Name (nm) (nm) Comment Name (nm) (nm) Comment L1 719 179 EMPTY R1 440 25 Blue Stereo R L2 753 20 Red Stereo L R2 754 19 Red Stereo R L3 673 16 Geology R3 803 20 Geology L4 602 17 Geology R4 864 17 Geology L5 535 19 Geology R5 903 25 Geology Left Filter Wheel L6 483 27 Geology Right Filter Wheel R6 933 24 Geology L7 440 25 Blue Stereo L R7 1001 28 Geology L8 440 20 Solar ND5 R8 880 20 Solar ND5

Table 1: Pancam Filter Characteristics Capabilities Projects Omega has extremely broad capabilities Omega Optical has years of experience servicing the professional astronomy mar- designing and manufacturing imaging system ket. Following is a partial list of filters sup- filters critical to astronomical and aero- plied to researchers, university programs, space projects and programs including: and government agencies. I AURA Obtained using 13-filter, 11-color Solar Observation I Canadian-France-Hawaii Telescope multispectral composites of H-Alpha Company selected soil, outcrop, and loose H-Beta I CONICA I ESA Mission rock targets, such as those in the Nebula and Cometary Studies I European Southern Very OII picture below, the visible to near-IR Large Telescope OIII images reveal mineralogical detail I GRANTECAN SII through characteristic reflectance I NASA JPL Star Dust Project CIII I NASA JPL Hubble Space Telescope: signatures. Images were obtained CII WFPC2 and WFPC3 Narrow bandpass by Spirit at the Gusev and I NASA JPL Martian Rovers 2003–2004: Opportunity at the Meridiani IR Astronomy Opportunity and Spirit J,H,K bands I Observatories of the Carnegie Institute Planum. Photo courtesy of Photometric Sets of Washington NASA/JPL/Cornell. Bessell (U,B,V,R,I) Johnson/Cousins (U,B,V,R,I) Stromgren (U,B,V,Y) Beta wide and narrow SDSS (u’, g’, r’, I’, z’) Thuan-Gunn

Other Detector Compensation Harris R Mould R-I Cover image courtesy of NASA JPL Hubble Space Telescope WFPC2 NGC 6369 The Little Ghost

© 2006 Omega Optical