Kosmos Stuttgart 110mm Schiefspiegler, a kit from 1964

In the summer of 2006, I had the opportunity to acquire a Kosmos 110mm Schiefspiegler telescope with a focal length of 2720mm.

It was built from a "Kosmos kit" by an amateur astronomer from the Lake Constance area.

A stamp on the back dates the optics to 1964 and identifies them as the work of optician Dieter Lichtenknecker, who was based in Weil der Stadt at the time.

I acquired the tilted-component telescope from my friend Uwe Weigele.

He had obtained it from an estate. To this day, the telescope is kept in its original old wooden "violin case."

Soon I was able to purchase second hand an original Kosmos eyepiece focuser from the stock of Hans-Ullrich Keller of Stuttgart, replacing the homemade one made of Pertinax.

The telescope was restored, and the tube was professionally repainted in white.

I finished the Schiefspiegler’s "cradle"—a base component commercial available at the time—and the mirror cell’s cover plate with a period-appropriate Hammerite hammered-effect paint.

Old brass parts, screws, and zinc sheets were allowed to retain the patina they had acquired over the past 60-plus years.

A defect in the primary mirror cell damaged the mirror, causing a conchoidal chip at the edge.

The compression springs for the adjustment screws had insufficient clearance from the edge of the primary mirror; during adjustment, the mirror would tilt and snag on the springs, resulting in the chip.

The problem was resolved by using springs with a smaller diameter.

Unfortunately, my primary mirror already had some damage on the front surface. Fortunately,

I was able to acquire a freshly recoated 110mm Schiefspiegler optics set—originally made by Dieter Lichtenecker in 1962—from the Solingen Public Observatory for my telescope.

This one also had damage, but only on the back!

Unfortunately, the mirror set didn't fit—for reasons unknown to me at the time! It was impossible to reach focus.

Measuring the primary mirror revealed a focal length of only 1360 mm instead of the specified 1620 mm!

That made Uwe prick up his ears. Acting on his tip, I found a "+" sign on the edge of the secondary mirror and a "-" directly opposite it! These markings point to a secondary mirror with a cardioid deformation—a very rare *Schiefspiegler* variant with an f/20 focal ratio! This will soon be clarified with Uwe's help.

Now I have a handsome vintage telescope of Swabian manufacture from the 1960s, as well as the mirror set for a rare *Schiefspiegler* (oblique-mirror telescope) kept in an old biscuit tin—which I passed on to Uwe.

Despite having slightly imperfect optics, my Schiefspiegler proved this week—during the 4th TTS, observing Jupiter and the Sun in white light with a Herschel wedge—that it is still a razor-sharp instrument.

-now I see chips on the edge of the mirror as patina :-)) -