Hampshire Astronomical Group

Celebrating 50 years (1960 - 2010)

12" Dome

The observatory complex's has a 12-inch (300mm) f5.5 Newtonian reflector which has been designed for CCD and electronic imaging, although one can use the telescope for visual observing.

The telescope has an aluminium closed tube, whereas all other reflecting telescopes on site have open surrerier truss designs. The value of a closed tube is it stops any stray light from entering onto the very sensitive detectors. The disadvantage is one can sometimes suffer from thermal tube currents which can degrade the image. This problem can be avoided by allowing the telescope and mirror to cool to the ambient temperature before the observing session this can typically take anything up to ½ to 1 hour depending on atmospheric conditions. There is now a mirror cooling fan fitted which help considerably with thermal disturbances.

The telescope is mounted on a fork mount and is computer controlled through commercial AWR electronics and software. This software does interface with standard PC hardware, although in an observatory as compact as this one, such computers are often felt to be rather bulky and so laptops are brought to the observatory for each observing run. This has the added advantage of avoiding damage to electronic equipment held in the damp unheated conditions that often prevail in an observatory.

The telescope was custom made by the renowned telescope maker Ron Arbour, who was well known for making 'one-off' high quality telescopes. The mirror was ground and figured by members of the Group. This has since been independently tested and assessed of having a high quality figure. The mirror cell and flat 'spider' was made by the late Norman Fisher.

In order to assist with tracking, a small auto-guiding telescope and CCD has been fitted and this helps considerably with tracking. This is also liked to auto-guiding software which interfaces with the main AWR drive.

The observatory dome, which is home made of fibre glass on plywood rib construction, has had some further engineering refinement on the dome rotation system and it now rotates with the push of a couple of fingers making access to the night sky much easier.

Through observational experience, it was originally noted that there was some thermal dissipation from the concrete walls, they have now been cladded with industrial building cladding and painted whiote to reflect much of the solar radiation. This has made a significant improvement to the thermal properties of the dome and the stars are now much sharper.

The inside of the dome has been completely painted in matt black. The internal walls have been further cladded and a vinyl floor laid over the original concrete base. An addition to the main telescope was the fitting of a 4 inch f10 refractor piggy-backed onto the main telescope.

This refractor was mounted in order to give the observatory further flexibility with the possibility of solar observing and also fitting another CCD camera in order to provide longer focal ration imaging.

The telescope has been used to image many celestial objects including the moon and many deep sky objects. For the recent Transits of Mercury and Venus, the telescope was fitted with a special white light solar filter and video images were obtained of the planet moving across the face of the Sun.

The telescope has also been used in tracking fast moving comets.