Moin,
hier eine Stellungnahme von Barry Pemberton, welche mich über Wolfgang Ransburg erreichte.
Mit der Veröffentlichung dieses Schreibens schliesse ich das Thema.
beste Gruesse
Matthias
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<i>Hello forum members,
Firstly, apologies for writing in English, my German is very bad indeed.
I would like to give all interested forum members an insight as to how we use our GPI Zygo for testing, primarily, paraboloids for Newtonians. Due to some 'Trade Secrets' I am not able to go into detail on some aspects but, please be assured, these areas have been developed with Zygo technicians and confirmed as accurate by The National Physical Laboratory in London.
Testing paraboloids consistently accurately with a laser interferometer is very difficult. Up to a couple of years ago we had a Zygo Mk4 interferometer which is a good instrument but has a couple of failings, both of which have been voiced earlier this week. To test an aspheric mirror with normal methods involves the use of a perforated flat of the same, or larger diameter and, at least as accurate as the mirror under test. Both the aspheric mirror, the Zygo and the flat have to be perfectly in line to carry out an accurate test and this can introduce errors if not done properly. Also, the mirror under test has to be reflective coated to carry out the test. If the mirror fails the test, the coating has to be removed, re-figured and then re-coated. so you can see, in a production environment this is not an ideal situation.
We approached Zygo and asked what a GPI would be able to do for us in terms of testing an uncoated, unfinished (possibly) aspheric mirror. Their initial response was exactly the same as the traditional method above, using a flat or, a slightly different method with a polished, small ball, which has similar alignment problems. In conjunction with Zygo we developed, prior to buying the GPI, a method of testing the mirrors without any reflective coating being needed and avoiding the problem of mis alignment. I am unable to elaborate any further here as the actual set up was expensive for us to develop and we consider it secret. At this point I would like to point out that many, many people have asked for more details on this process but unfortunately we have had to politely reply that we are not prepared to go into further details. Of the many people who have asked questions of this aspect, all but two have understood the secrecy of the set up and accepted our explanation. The two who didn't and went to great lengths to find out by threats etc, still appear to be aggressive to Orion Optics.
We validated the procedure by testing a mirror with the assistance of Zygo technicians and then sent it to The National Physical Laboratory very close to London. The results were so close as to be virtually indistinguishable. with this confirmation and the procedure finalised, we bought our GPI from Zygo along with some additional accessories and testing hardware.
We now can test, because of our set up procedure, flats, spheres, ellipsods, paraboloids and hyperboloids without having any coatings present on the mirrors. This enables constant monitoring of our production stages from polishing to final coating. We even test, on a random basis, an uncoated mirror and then coat it and re-test. This gives quality assurance to the coating evenness, its reflectivity also measured on our Lambda 25 photospectrometer.
I would dearly love to be able to be an active member of this forum but feel that because of accurate translation problems and the residual ill feeling from a year or so ago, it would not be realistically possible. However, if any one has a technical question which they would like to ask me directly I will give as full and accurate reply as my knowledge and process information will allow.""""
We would prefer to leave the German forums to you to monitor.
Regards
Barry
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