Located under southern Australian skies, our suburban backyard observatory is located under dark skies in the state of NSW, Australia. We are currently touring Australia with our portable 8" f/4 astrograph looking for dark skies to photograph the Australian night sky.
The primary imaging telescope (the one used to take photos) is a customised 305mm (12-inch diameter) Newtonian reflector telescope with a fast photographic f/ratio of f/5. When teamed with a Multi-Purpose Coma Corrector (MPCC) from Baader this telescope is ideal for deep-sky imaging.
The telescope made by GSO Optical was supplied by
The Binocular & Telescope Shop as a dobsonian telescope. I then
took the optical tube assembly and modified it to better suit astrophotography.
Such modifications consisted of
improving the telescope's image contrast by installing light baffles inside
the telescope tube - this modification improved the contrast tremendously
both visually and photographically. Other modifications included stopping stray light from entering the telescope
around the focuser mount and especially the primary mirror mount.
The primary telescope was fitted with a 2-inch Crayford-style focuser with a 10:1 micro-focus and 2-inch camera adapter. Focus is achieved using DSLR Focus software software and a USB connection from the laptop to the camera which returns snapshots to the computer screen where you can check for good focus.
Telescope custom mount.
This entire collection of equipment is all mounted to the top of the equatorial mount head with brackets and fittings that I made in my own backyard. The Losmandy saddle plate is replaced with my own 12mm thick aluminium plate which uses all six mounting holes on top of the equatorial head. This large aluminium saddle-plate seats two hand made tube seats which then seat the optical tube assembly (OTA). The OTA is then held in position with luggage rack straps which are tension adjustable enough to crush the OTA, they certainly do a good job of holding the OTA in position.
The imaging camera is a 8 Mega-pixel thermo-electrically cooled Canon 350D Digital SLR camera modified for astrophotography work. I modified the camera by removing the manufacturer's filter over the image sensor and replaced it with a clear optical glass filter that I purchased from Edmund Scientific. This modification permits the camera to see further into the spectrum where objects like nebula emit their light.
The guidescope is an old Meade branded 4.5-inch f/9
Newtonian reflector that I originally purchased from a local optics dealer
many many years ago. The guidescope is mounted and pointed with Bonney
Lake Astro Works 5.5" guidescope rings and a modified dovetail rail
intended for a 10" Schmidt-Cassegrain telescope that I fitted to my own
docking plate. Usually is used with a 1.8x Televue Barlow
guiding at f/16.
I built the observatory from a flat roof heavy gauge 2.4m x 3.0m garden shed. I was careful not to choose a garden shed made from dozens of small panels, rather I selected a manufacturer who provided each wall as a complete panel so that the complete shed is only 5 panels (each wall and the roof).
I split the roof into two halves, each side of the roof slides open partially or fully. Castor wheels fitted to the underside of the roof, travel up a carved timber beam when the section of roof is pulled open. This has the effect of lifting the roof off the walls and carrying the roof weight on the wheels so that the roof easily slides open. When the roof is pushed closed the wheels travel down the timber channel so that the roof perfectly sits on the walls just as it completely closes. The roof is then latched down to a 100x25mm timber beam that is ramset around the inside perimeter of the observatory walls. Truss angle brackets also join these beams at the corners. This makes the entire observatory very rigid and strong, particularly when the roof is off.
Once the roof is closed, a number of gate-lock latches are used to secure the roof to the inner perimeter beam.
The walls of the observatory are sealed
from the inside with clear weatherproof sealant and roof is sealed to the
walls using foam inserts cut and glued into position. During extreme wind
conditions a 3 metre long 150x50mm treated pine timber plank is placed on
the roof to assist the roof in remaining where it belongs.
The observatory sits on a concrete slab I made 150mm thick with 500mm deep 350mm square pier footings in each corner of the slab. The centre 1-metre of the slab is thicker, 200mm+, and the slab is reinforced with 2 layers of F72 (7.2mm) steel fabric, one layer near the bottom and one layer near the top of the slab.
I ordered the concrete for the slab to be a high strength mix, meaning that the concrete supplier will use more cement in their mix than usual. When these types of slabs begin to dry they have the appearance of looking greenish due to the higher amount of cement used in the concrete, this adds to the expense of the slab but the strength will much higher than that of a normal slab.
2007 - Paul Mayo PaulandSylvia@campingunderstars.com