Lens alignment accuracy

The newly announced Stellarvue SV135 f5.4 Dual-Fluoro Triplet is 'posed to have its elements aligned to an accuracy of 3 microns throughout. Does anyone know what "typical" alignment accuracy is for a apo from Tak, TV, AP etc ??
Thanks,
Robert

It can be hard to re-aligh if it goes out of alignment!! 8O

Dmitri

To answer your question directly, it is typical to edge and center each individual lens element in a triplet apo to an accuracy of .0001" wedge tolerance (which is approximately 2.5 microns). I don't know any of the top apo makers that do not routinely achieve this minimum level of accuracy in their centering.

Each element is normally edged as a unit on the same machine in sets of three so that they come out with the same exact diameter. They don't need to be exact, but it makes final adjustment easier.

The elements are then placed into a cell where the edge positions are held by the cell wall. The spacers between the elements must be held to a thickness tolerance of approximately 1/2 tenth (.00005"). Even then the final adjustment of the spacing is usually tweaked by carefully polishing off an infitesmal amount of material until all signs of coma are gone. This is done during the final alignment process. It compensates for any wedge in the glass or the spacers and spacer positions. Another way to do it is to provide 3 screws around the periphery of one of the elements which allows the optician to move the element sideways to counteract coma. It is not a precise way to do it because it inevitably introduces a tiny bit of lateral color, but it is the easiest, fastest and cheapest way to do final alignment.

Roland Christen