Two 200mm dia. medium band interference filters. Note black aluminum ring around the perimeter to facilitate handling and mounting.
270 mm dia. medium-band interference filters.
Since the advent and widespread use of CCD detectors in the 1990's,
research astronomy has depended upon optical filters to obtain accurate,
calibrated, and astrophysically interesting measurements. Whether obtaining
images for broad band photometry, mapping narrow band emission line
distributions, or obtaining spectral energy distributions in spectroscopic
instruments, reliable, high quality, precision optical filters are a
key component of the instrumentation.
Custom Scientific, Inc. has been dedicated to supplying research
astronomers across six continents with such optical filters and other
optical components since 1990. Members of our team have worked on filters
for a wide range of astronomical installations including WFPC/2 that
is now in orbit in the Hubble Space Telescope. We have played a principal
role in developing and refining many of the photometric filter systems
in use today, including Johnson, Cousins, Bessell, Stromgren, Thuan-Gunn,
Harris, IRWG Young-Milone, SDSS, tri-color RGB, DDO, Vilnius and BATC
among others. Each filter is shipped with its own transmission spectrum
in analog or digital format.
As CCD's have increased in size, and as cameras are utilizing ever-larger
arrays of CCD's, the requirements for filter sizes are increasing. We
are very experienced in these large format filters and some examples
are shown on this page.
Also, please note that we also make mirrors, beamsplitters, dewar
windows and many other optical components. Send us your specifications
and we will send you a quote.
We do not have a published price list for the these optical filters
because so many astrophysics observing programs tend to have custom
requirements such as wavelength, bandwidth, redshift, size, and shape.
Therefore, for pricing please contact us
and we will quote you pricing based upon your specific requirements. If you want to consider lower-cost
filters that are usually in stock, please check our list of filters
for amateur astronomy, which includes the
most common photometric and emission line bands in smaller sizes.
A Customized filter wheel.
A 50mm dia. medium band interference
filter with a small, circular coated spot in the filter's
center which is a calibrated neutral density coating (ND1,
T=10%). Note how the graph in the photo shows the transmission
through the part of the filter without ND coating (T>90%)
overlaid with the spectrum through the part of the filter
with ND coating (T=10%). The filter is located near a telescope
focus plane and the neutral density spot can be positioned
to reduce the intensity of a bright star by 90%, yet allow
full transmission of objects close to the star.
Large size, narrow bandpass
filter, 12 x 12 inches (300 x 300 mm). Due to the narrow
bandwidth of this filter, it was fabricated as a mosaic
of four elements 150 x 150 mm each and mounted in a custom-
machined aluminum frame.
Rectangular narrow bandpass filters
for the M2FS multi-object spectrograph.
A 160x160 mm bandpass filter (left)
and a 50x50 ultra-violet filter (right).
7-position, automated filter wheel for
80 x 80 mm filters. The clear aperture is 74 x 74 mm.
Large narrowband filter in anodized aluminum ring.
7-position, automated filter wheel
for 80 x 80 mm filters. The clear aperture is 74 x 74 mm.
Gold coated, λ/10 mirrors. Gold
mirrors have high reflectivity in the infrared.
Housing and contents for liquid
CuSO4 filter. This combination of glass
UV optical filters forms a hermetically sealed cavity that
holds a volume of blue liquid CuSO4. This unique
assembly provides a UV filter that has high transmission
in the ultraviolet and good blocking of unwanted visible
and near infrared light. Photo inset shows magnified image
of nylon set-screw that seals hole used to fill cavity.
When filter is filled, set-screw would be hidden inside
filter housing. A jar of CuSO4 is in the background.
Typical filter spectra
H-alpha 656.3/4.5 nm