This telescope was moved from the RGO site at Herstmonceux in 1979 and after re-engineering work
done at Grubb Parsons in Newcastle was the first to come into operation on La Palma in 1983. The large
building was designed for the requirement at the time to accommodate the f/50 Coudé focus with two optics
laboratories on the second floor, but this was never commissioned.
The mechanical, electrical and electronics workshops are also housed in this building along with offices
for staff. However, there were always problems with heat rising from the offices into the dome so these
days most staff have office space in the WHT annex or work at the ING sea level office in Santa Cruz.
I found it quite difficult at first navigating around the building as the stairwells at the east and
west entrances are very similar not to mention the vast amount of heat lock doors one has to pass through.
Its quite a maze inside, but I soon got used to it!
The INT is an equatorial fork mounted telescope and can work at f/3.29 (corrected prime focus) or f/15
at Cassegrain. The telescope weighs 90 tonnes and the polar axis disc floats on a film of oil forced under
pressure through a series of pads mounted below and behind the disc. The telescope is so perfectly
balanced in that if the free motion clamps were released, it is possible for a single person to move the
structure by hand... I did it once when we thought there were problems with a bearing.
A photo of the INT building after it had been re-painted several years ago. I think it looked better
with the red solar screens!
The INT in 1986 fitted with the original prime focus CCD camera
The plaque reads: NEI GRUBB PARSONS, Isaac Newton Telescope, 2.5m reflector, 1967,
Resited and renewed 1983
The Cassegrain instrument configuration in the 1980's.
The blue racks contained the power supplies and controller for the Image Photon Counting System
This detector was certainly the most complex piece of equipment we had to maintain. If it hadn't
been used for a time, it required a 'bake out' period of several hours when the temperature of
the water circulating in the cooling jacket around the image intensifier tube was raised to dry
out any dampness. As the tube operated with a 40 kilovolt supply this was important to prevent
Bringing up this instrument at the start of an observing run was always a nerve racking
experience as problems sometimes occurred. When photon events seen on a small display monitor
started to appear as the voltage ramped up, it gave one confidence that all was working.
The IPCS was eventually phased out when CCD's that could work efficiently at blue
wavelengths were introduced, but I doubt if even today they perform as well as the IPCS did
as a blue light detector.
This image also shows the infamous open well below the step ladder on the polar disc. The
story goes that a support astronomer fell into it one night! After the incident the well was
closed off and the entire observing floor wood panelled.
The Isaac Newton Telescope in 2005
A few years ago the telescope was re-painted and has lost its 'two tone' appearance as can be
seen in the 1986 image above. For more than 2 years it has been operating using only the Wide
Field Camera at prime focus, but later this year the Cassegrain Spectrograph (IDS) as seen in
the image to the right will be offered again as a common user instrument.
Showing the motorised counterweight system
I suggested this as an idea in the mid 1990's to the mechanical group and it was accepted and built.
Previously, electronics racks from the Cassegrain turntable were removed and heavy weight frames
fitted when changing to prime focus imaging. Now its simply the case of moving the weight boxes
up or down depending on whether the secondary mirror or wide field camera is fitted. This also has
the advantage of halving the time to do the instrument change to prime focus plus the Cassegrain
instruments are always available to allow spectrograph setups or engineering work to be carried out
during prime focus observing.
The telescope at the Access Park position
During the day when observing at prime focus, the telescope is left in this position to allow
the CCD camera cryostat to be filled with liquid nitrogen and to change the filters within the
Wide Field Camera if needed.
Looking down from the balcony with the primary mirror cover petals opened.
THE INT WIDE FIELD CAMERA (In use since 1997)
The CCD camera consists of four EEV 2K x 4K chips mounted in the blue cryostat and servoed at
a temperature of 153o
C) using liquid nitrogen to minimise
thermal noise. The WFC is fitted onto the original prime focus rotator, but in practice this
never needs to be moved. A large format CCD chip used for autoguiding is mounted alongside the
science chips and can usually detect a suitable guide star.
for more information on the wide field camera and some nice images.
Click here to have a look around the INT control room.