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Testing optics
We re contacted regularly with customers who wish us to re-coat their mirrors and who wish to have an optical test carried out prior to carrying out the re-coat to put their mind at rest that the mirror in question is actually worth both the effort and expense. We are also asked, again quite regularly, if we can carry out thorough optical tests on their complete telescope or single optical part.

Below is a list of prices which is by no means fully comprehensive. It will however answer most of your price queries in having an optical component(s) tested.
To discuss the tests briefly first to allow you to judge which, if any of these tests are what you consider appropriate for your needs.
The tests re grouped into 2 basic areas, Interferometric tests and non interferometric tests. As the name suggests, one uses an interferometer, the others don’t. One group is expensive, the other not so. One group has an accuracy of up to 96%, the other is limited up to 80%

Interferometry Testing
Interferometric tests we carry out are done by implementing our GPI Zygo and other ancillary equipment including an air table on which your optic/telescope is mounted along with the whole Zygo to remove as much as possible of vibrations and smooth out the ones which still manage to get through this dampening system. The testing lab is air conditioned for consistent temperature into which your test object is place and left for 24 hours to schieve temperature stability. If you care to click on this link the whole arrangement of our Zygo will be revealed.

This testing method is lengthy and quite technically involved. It will reveal and report the slightest errors if present in the object under test to a level which will in most instances, be above what you or most people need. The printed report is a document which is respected world wide and is accepted throughout the optical world. Our Zygo on numerous occasions has settled battles between many customers and their telescope suppliers where the shop or dealer has refused to accept that the customer has a definite problem with the telescope but the shop is more than reluctant to accept liability. Our Zygo has been used in several legal cases and has always, without exception, come down firmly on the side of correctness, be it either the dealer or customer, it doesn’t take sides, it just tests and reports the truth about optics being tested. All these type of tests are including a full Zygo graphical report.

Non Interferometric tests
These tests can be varied in application depending on what the customer wishes to have measured or displayed. They use primarily white light, microscopic pin holes, very fine Ronchi lines, colour filters etc. The results fot hese tests are able to highlight any problems with images the telescope produces, star images distorted, fuzzy, problems around the field edge, telescope won’t focus at all, false colour visible etc, etc. These tests although capable of detecting very small errors, they are not easily used to measure the accuracy numerically or as accurately as the Zygo does but, overall, with the technician’s experience, he can after carrying out these tests, make a decision on the accuracy on the optic/telescope under test to within 80-85% of the actual accuracy that the Zygo would be able to display. Around 90% of all the tests we carry out for external customers are within the non Interferometric test band.

As mentioned above, we can’t cover here every possible telescope design, refractor, reflector, catadioptric, size, make, speed etc but, the table will give you a very good idea and something to work with and enable you, if so required, to contact us with a plan of action at a cost quite close to actual. We can if so requested give a full typed report on the test if you so wish. Or, as a large proportion of customers request, a verbal confirmation is adequate. The choice is yours.

Which ever test you decide on, we always collimate your telescope as good as is possible prior to the test.
 

Non interferometric tests

Aperture

Newtonian type
Reflector

Cassegrain type
Reflector

Refractor

Objective lens only

Primary mirror

Secondary
flat mirrors

75-114mm

20

20

25

35

20

n/a

115-160mm

22

22

30

45

22

n/a

161-220mm

25

25

40

60

25

n/a

221-260mm

30

30

50

90

30

n/a

261-300mm

35

35

n/a

120

35

n/a

301-400mm

40

40

n/a

n/a

40

n/a

400-500mm

60

60

n/a

n/a

60

n/a

501-600mm

80

80

n/a

n/a

80

n/a

Full typed reports 25

Interferometric tests ZYGO - Fizeau

75-114mm

n/a

75

75

100

75

n/a

115-160mm

n/a

75

75

100

75

n/a

161-220mm

n/a

90

90

135

90

n/a

221-260mm

n/a

100

100

150

100

n/a

261-300mm

n/a

140

140

225

140

n/a

301-400mm

n/a

160

160

n/a

160

n/a

400-500mm

n/a

190

190

n/a

190

n/a

501-600mm

n/a

240

240

n/a

240

n/a

Secondary
flat mirrors

Flat secondaries Under 50mm

n/a

n/a

n/a

n/a

n/a

5

Flat secondaries 51-100mm

n/a

n/a

n/a

n/a

n/a

15

Flat secondaries 101-180mm

n/a

n/a

n/a

n/a

n/a

25

All include full Zygo graphical reports. Prices do not include VAT

You may also be interested in these pages:

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OPTICS : Telescope Mirrors : Elliptical Flats : Mirror Cells : Zygo : Optics Finish Note : PV Explained
Mirror Recoating : All About Optics : Optical Coatings : Optical + Telescope Testing

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