We start with only the finest quality! Fine or precision annealed low
expansion borosilicate glass substrate, Schott Supremax 33,
unless otherwise noted. Each substrate is tested under polarized
light for internal strain and striae. No work will commence on any
substrate unless it passes this test, including optics sent to us for
re-figuring. All of our substrates are free of any edge chips.
After diamond generation, fine grinding, polishing, and figuring, each
optic receives several hours of testing in our atmospherically
controlled shop. We use not one, but several precise optical tests.
The results from each test are cross-checked against each other in
order to provide an accurate qualitative and quantitative assessment
of the optical quality.
Our testing methods include.
*Foucault-Null Test: Used to obtain a reading of the overall
correction and to inspect the optical surface for smoothness. The
overall correction reading provided by this test is verified against
results obtained from Interferometry. In most cases we use a double-
pass null test.
*Figure of Revolution Test: Used for detecting stress induced flexure
errors and astigmatism. The primary mirrors manufactured at
Ostahowski Optics, Inc. are tested in the horizontal optical axis using
an optical mounting sling. The most common and severe stress
flexure aberrations are astigmatism and trefoil. Each optic receives
extensive testing to determine if the optical surface is exhibiting
stress flexure or true astigmatism. The astigmatic error that is not
induced by mounting stress is always removed during optical
figuring. Every primary must pass this surface of revolution test.
*Interferometric Testing: Interferometric testing is the standard that
aerospace industry, professional optical labs, government labs, and
well informed consumers, use for a quantitative assessment of the
optical wave front quality. Interferometry is a time consuming and
expensive process requiring a high degree of technical expertise. It
produces accurate test results enabling us to consistently produce
outstanding mirrors. This is the final test that all Ostahowski Optics,
Inc.. mirrors undergo and must pass.
We employ several different types of interferometers, each
has a specific use depending upon the optic, or system. During
interferometric testing the shape of an optic's wave front is
determined by superimposing its wave front over a reference wave
front that is certified to be highly accurate. Constructive and
destructive interference created between the superimposed wave
fronts generate the interference fringes. A CCD camera is then used
to capture an image of the interference fringes and send it to a
computer. Interferometric fringe analysis software is then used to
analyze the data points along the fringes and accurately determine
the deviation between the two wave fronts. Interferogram averaging
minimizes the effects of any air currents that may be in the light
path during testing providing accurate information about the true
wave front quality. The fringe analysis software then generates us a
detailed report. Mirrors certified by zonal Foucault test rarely attain
the same quality of results when tested by an interferometer and
almost always overstate the quality of the mirror being tested.
Test Data Provided
Ostahowski Optics, Inc. test data reports contain the following
Strehl Ratio (primary optics and optical systems)
RMS Wave front Error
Peak to Valley Wave front Error
Wave front Map
Fine grind inspection
After polish Inspection
Surface of revolution