THE FRED BEST 18 INCH TELESCOPE

Named in the memory of Fred Best who founded the Croydon Astronomical Society at his home in 1956. It is said that it took 18 years to build... An inch a year! Norman Fisher (ex-chairman of the CAS who sadly succumbed to cancer in 1994) was without doubt the driving force behind the project. Without his time and effort there would be no Kenley Observatory today. The engineering work was done by Gordon Main in his home workshop and at no expense regarding his time to the society. Due to the intensity of the project, his health and marriage suffered the consequences. I knew them both well and will always hold the greatest respect for them.

Many people were involved with the optics, notably F.J. Hargreaves who procured the 18 inch mirror blank and who's company Optical Surfaces in Kenley did the grinding and figuring. I recall Norman telling me that the Cassegrain secondary mirror was later re-figured by Horace Dall. He along with Hargreaves were probably the finest opticians in the UK during the 20th century. I maintained the telescope's electronics up to when I left the UK in 1986.

The telescope was novel in that it had two optical arrangements. It could be used as a Newtonian (F4) or as a Cassegrain-Nasmyth (F20). The latter bringing the focus out through the east fork of the declination axis. Moving between foci simply involved changing the optical element at the top end of the tube, either the Newtonian flat or the Cassegrain secondary mirror. I used the telescope many times at both foci, but my most memorable night was visually observing the Orion Nebula (M42) at the F20 focus. The fine filamentary detail was amazing with an effect like a 3D view through the nebula.

Due to advancements in telescope design and control, the CAS sold off the FBT in March 2005 much to the dismay of some of the older/ex membership (me included) and now have a Meade LX200 14 inch SCT installed in the Kenley Observatory (now renamed the Norman Fisher Observatory). I sincerely hope the new owner appreciates what a classic telescope they have and of the toil and effort of those people who brought the project to completion. (Photos taken during a visit in 1993)

INAUGURATION DAY AT THE KENLEY OBSERVATORY   30th June 1979

Unfortunately the only photo I have of this event. I recognise Keith Brackenborough in the centre and Catherine Pillinger (nee: Dowland) just behind him. The person standing close to the entrance looks remarkably like Paul Murdin; one of the earliest members of the CAS and who was the head of the La Palma Operations Division at the RGO when I joined in 1986. I'm looking on (with girlfriend) to the left in the foreground.

A GENERAL VIEW OF THE TELESCOPE

The images above show the detail of the declination slow motion drive mechanism. A 'banjo arm' coupled to the declination axis (via friction pads) allowed the telescope to be manually positioned. The slotted clamp with adjustment bolt at the top of the arm setting the amount of friction required for manual slewing. Small +/- adjustments in declination could then be made using the handset which ran the motor on the fork arm driving the banjo arm through a leadscrew and nut. Interestingly, very similar in operation but of course on a much smaller scale to the 2.5 metre Isaac Newton Telescope (INT) on La Palma.
Looking down the tube with the mirror covers opened.
The tertiary mirror mount (tertiary flat not fitted) can be seen within the central box section. From what I recall this was a bayonet arrangement. The idea being that the mirror cell would realign itself to the optical axis if removed for cleaning. There was a similar mechanism for the top end optics, but in practice this never worked well and perfect collimation was seldom achieved when switching between foci.

These images show part of the unique RA twin worm drive designed by Norman Fisher.

The worms driving the main wheel are themselves driven through a worm. The worms were carefully adjusted so that one acted on the leading edge of a main wheel tooth, the other on a trailing edge. This effectively removed most of the backlash from the system which would have been much greater using a single worm drive.


Page updated: 22nd July 2010