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22 inch F 3.4 Mirror recently
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Iris Nebula: image by
using optics made by Nichol Optical
Optical is a business dedicated to making high precision
astronomical optics. I have been making astronomical optics for in
excess of 30 years and have supplied optics to customers in
Germany, France, Belgium, Denmark, Sweden, Netherlands,
Ireland, Japan, Slovenia and South Africa as well as the UK.
To ensure my optics are of the highest quality a variety of
tests are used. Together with the more traditional Foucault
and Ronchi tests I also employ the Ross null test (using a
certified lens), and the
double pass null test or, autocollimation test as it is also
known. These are well established tests and are used
widely by professional optical shops the world over.
Parabolic mirrors are generally finished using the Ross null
test or autocollimation test, these tests are quantitative
in nature and do not produce a set of numbers describing the
mirrors surface. I do not produce a test certificate giving
a detailed numerical analysis of a mirrors surface.
With a null test a perfect mirror produces straight bands
when viewed with a ronchi grating, any curvature of the
bands indicates the amount of spherical aberration present.
For a given mirror a computer simulation may be generated
showing the degree of curvature in the observed ronchi bands
for varying degrees of spherical aberration. In order to
assess a mirrors surface the observed curvature of the
ronchi bands is compared with a computer generated image.
With experience this test method is easily capable of
revealing wavefront errors of 1/8 wave and smaller.
more information about optical standards please read the
notes on my articles
page. Perhaps the best recommendation for any optic
is confirmation of it’s performance in a telescope, I am
pleased to say that I have received much feedback from
customers who have been delighted with the performance of
their optics, for further information please see the