Fork mount
The fork mount is a type of bracket for telescopes . It is used on the one hand with many large telescopes, on the other hand often with amateur telescopes (for example from Celestron , Meade ). The fork mount is suitable for parallactic mounting for medium and high geographical latitudes , azimuthal mounting for all latitudes. It is not suitable for different telescopes, but is always specially designed for a certain optical tube. It is ideal for short lengths ( Cassegrain telescope , Ritchey-Chrétien-Cassegrain telescope ), less so for longer tubes ( Newton telescope , Kepler telescope ). With conventional, equatorially mounted fork mounts, the fork is rigidly connected to a more or less long hour axis. This, in turn, is supported by two roller bearings that are as far apart as possible in order to keep the bearing stress low due to the high cantilever load. According to the much better construction by Rudolf Pressberger ( Purgathofer observatory , Davidschlag observatory ), there is no "visible" hour axis. The fork support is partially shifted into the fork itself and reduced to a small, and therefore low-friction, support bearing near the center of gravity. The cantilever load on the bearing is significantly lower. The drive element itself takes over the definition of the hour axis. This new type of fork mount was published 20 years ago in the magazine “ Der Sternenbote ” under the name “New Austrian Telescope Precision Mount” (ÖPFM) . In Austria, seven telescopes with mirror diameters between 40 cm and 100 cm have been built very successfully based on this construction.
A special form of this type of mount is the one-armed fork mount . This is one of the more recent developments, with the advantages of a significant weight reduction while saving space at the same time. The models of the more recent times (see illustration) manage entirely without a counterweight, as the main axis is movably mounted so that the mount can adapt to the weight it is expected to carry. However, the cantilever load on the bearings is high again and occurs in both axes.
A disadvantage of some commercial fork mounts is the susceptibility of their undersized arms to vibrations, which could only have been managed by a stiffer construction that would increase the weight again and was therefore not used.
The advantage is that the telescope does not have to be broken through, so you can keep the exposure running for astro images when the object passes through the north-south meridian. Schmidt telescopes are therefore almost always mounted in a fork in the professional sector.