I deceided to contstruct a 13" f6 dobsonian telescope to observe the some fainter deepskyobjects.

I grinded the optics in the year 2007/2008. Final foucault testing using couldermasks was done with several persons.

It seems that the mirror was almost 1/8 lambda.

After a Monte-Carlo analysis it seems that we can safely assume that the mirror is 1/7 lambda.

However, with a startest I detected astigmatism in the primary mirror. I deceided to reparabolyze the mirror. I'm still in the progress of doing that.

The astigmatism is very good seen with a detailled foucault test.

The ronchitest also shows a hint of the astigmatism. With a wiretest (no pics) it is obvious that the source of the error is astigmatism.

The telescope itself was finalised in summer 2008. The mirror sits safely in a 18-points sling mirrorcell.

The effects of the mirror-deformation under its own weight is easily calculated with a PLOP-simulation. Here it seems that 18 points is the best solution for minimize deformation.

This is the final telescope. Remarks the curved spider to minimize spidervane effects on bright stars and planets.

After a interferometertest of the secondary it seems that here we also have some problems. This is probably caused by the silicone to which the secondary is glued to its holder.s