Observatory

 

The observatory is a Sirius Observatories 3.5 metre diameter dome. It is located on a suspended slab built over a large family room. The slab is 170 mm thick reinforced concrete. An integral reinforced concrete beam runs across the width of the slab in order to provide a stable imaging platform. This arrangement has avoided the need to run a concrete pier from the telescope base down through the family room into the ground. Not visible is the upper shutter which has retracted back over the other side of the dome.

 

The image at  left shows the doorway leading to steps down to the family  room. In this view the dome's lower shutter is closed. The upper shutter is fully open, having rolled back over the rear side of the dome.

 

 

This is a view from the front drive. The structure on the roof to left of the dome is a light box. It allows light into the family room from the north during winter months.

 

This is a view from the back garden. A water ring main and sprinklers can be seen running around the edge of the slab. It is fed by a petrol pump from the 33,000 litre concrete tank which is visible at bottom right. The large windows are also protected by motorised (manual override) shutters. These precautions are necessary because fires and high winds are common in the summer months.

 

 

The black housing contains the battery and electronics which operate the upper dome shutter. A solar panel is located on the outside of the dome immediately behind the housing. The white box contains the dome rotation battery, motor and electronics. The motor drives the toothed bar which runs around the lower part of the upper dome. A second solar panel is on the outside behind the white box.  Auxiliary power is provided to the dome rotation controller by a DC power supply located in the storage compartment (shown).  The dome and shutter can be controlled by computer or by manual override switches.

 

 

The MaxDome board, from Diffraction Ltd. in Canada can be seen at top left. The coil is for the wireless connection between this board and a similar board located in the black dome rotation housing shown in an image above. The white cable at bottom left of the board is a serial connection to COM 2 of the controlling computer. The manual dome rotation switch is hanging off the right side of the box. The red switch on the left of the box is the power ON/OFF switch for the MaxDome board. Since this board was installed there have been some changes to the recommended installation orientation and location of the two MaxDome boards in order to ensure reliable wireless communication.

 

 

The D.C. power supply ensures proper dome rotation even after heavy dome use and repeated days without sufficient sunlight to charge the battery.

 

 

This box houses the relays and other circuitry required to open and close the lower shutter. Note the manual override switch.

 

Telescopes

 

 

The main telescope is a 10-inch Meade LX200GPS Schmitt-Cassegrain. It is mounted on a Meade equatorial wedge. When the Optical Tube Assembly is parallel to the forks the telescope is pointing at the South Celestial Pole. This polar alignment makes it possible to take long-exposure photographs with minimal movement of the stars in the image.

The piggybacked telescope is an Orion ED80 refractor. It serves sometimes as a guide scope for the LX200GPS and other times as the main scope with the LX200GPS serving as the guide scope. A Losmandy dovetail plate and rings connect the ED80 firmly to the LX200GSP.

 

 

Heated dew remover strips can be seen around the objective lens' of both telescopes. A dew shield is never needed. A rail runs the bottom length of the LX200GPS and holds two sliding rods each of which has counterweights. Such a system is necessary in order to get proper counterbalance of the auxiliary scope, cameras and accessories. The lower counterweight rod is hidden behind the telescope forks.

 

 

The electronic controller for the dew heater strips can be seen at right centre. The boxes to the right of it are the D.C. power supplies for the two Canon cameras which are used interchangeably. The cables connection to the Meade LX200GPs are (from left to right) the 12V DC power, the connection to the Meade microfocuser, the connection to the telescope handbox ( which is visible at right but seldom used) and the serial connection to COM 1 on the computer.

 

 

The clear plastic box contains the D.C. power supplies for the dew heating equipment and for the LX200GPS telescope. The silver boxes at top center are part of the USB extender cables which connect the cameras back to computer. Note also just left of centre on the ground is a white switch. It is used to break connection between the computer and the Canon SLR camera long-exposure (> 30 second) trigger. It was decided to initially use the standard telescope tripod rather than a custom pier in order to gain experience as to the optimal location and height of a future pier. In reality a pier would add nothing to performance and is not a high priority.

 

Cameras

 

 

Above is the 8 megapixel Canon EOS 350D digital SLR camera which connects at prime focus to the LX200GPS via a Meade f /6.3 focal reducer. The focal reducer is contained in a TA2P 2-inch adapter sourced from Scopestuff. The adapter along with a matching T-adapter ring connects the camera to the microfocuser on the telescope. The TA2P splits apart allowing it to be used either with or without a focal reducer. It also has a female thread inside its 2-inch barrel into which various filters can be screwed. Cables connecting the camera are (from left to right) the shutter controller, the USB image transfer and communications cable and the power cable to the fitting which replaces the camera's DC battery this allowing mains powered operation.

A second camera, a 6 megapixel Canon EOS 300D digital SLR, is used interchangeably with the camera above. As well as having fewer pixels it also has a slower, USB 1.0 connection. In practice this is not a significant problem because the high resolution RAW images are generally held inside the cameras during imaging sessions.  The EOS  300D had been modded, which is to say I have opened it up and removed the UV/IR filter window which is located inside it (just in front of the CMOS image sensor). The filter has been replaced with an AR coated optical glass blank which passes the H alpha wavelengths to a much greater degree than does an unmodded camera. Unfortunately it then also passes unwanted IR wavelengths which can lead to star bloating. To avoid this a narrow-cutoff, high-transmissision UV/IR filter is screwed into the TA2P adapter. It passes the H alpha wavelengths.

 

 

The guide camera (also usable for planetary imaging) is a Deep Sky Imager from Meade instruments. It is relatively inexpensive and makes it possible to guide on stars down to about magnitude 10. It is powered from the USB cable which connects to the back of the computer. Between the DSI and the Meade 2-inch diagonal is a 2X Barlow which doubles the focal length of the Orion ED80 from its native 600 mm to 1,200 mm. This meets to requirement that to focal length of the guide scope be at least half that of the telescope used to to the imaging. The 10-inch LX200GPS has a native focal length of 2,500 mm. The diagonal is needed to enable the DSI  to be brought to focus.

 

Computer

 

 

All telescope, camera and dome control is done from this computer. Images are downloaded to and processed in this computer. The LCD clock is also a temperature thermometer and is used to check the temperature at which camera dark frames are taken.

 

 

On the top of the computer can be seen the wireless access point which connects via wireless to an ADSL broadband modem which is located in the house below. Cables into the rear of the computer, working from the top down are,  the COM 1 serial cable to the LX200 GPS telescope, the cable connecting the parallel port to the Canon SLR shutter control (drive transistors are located inside the shell of the connector), the COM 2 cable to the stationary dome controller, and separate USB 2.0 cable connecting each of the Canon digital SLR and the Meade DSI.

 

Software

A typical imaging session comprises powering up the computer, dome, telescope and cameras and then bringing up the POTH (telescope and dome hub) screen on the computer. It is used to connect to the dome and, if necessary to bring it to it's home position. It is also used to remotely open the upper and lower dome shutters. 

Software Bisque's The Sky planetarium program is then started and connected to the telescope's serial port via the POTH hub. By clicking on a bright star shown on the computer screen the telescope slews to point to it and the slit of the Sirius dome follows automatically. During the imaging session the dome remains synched to the telescope even to the extend of making periodic adjustments during an extended, automated imaging session.

Diffraction Limited's MaxIm DL software is then started and connected to the Meade telescope via the POTH software hub (thus The Sky and the MaxIm  DL share the telescope's COM1 port) and also to the Canon DSLR and Meade DSI cameras. An image is taken through the Canon DSLR and MaxIM DL used to centre the star on the computer screen. A synch operation is then performed in The Sky. Focusing of the Digital SLR is then done using a Hartmann mask and by 400% magnification of images on the computer screen, using small faint stars.

The Sky program is then used to direct the telescope to go to the desired object for imaging.

Final alignment is done in MaxImDL which has controls for very precise pointing of the telescope. A guide star is found in the FOV and the MaxIM used to to do an initial guide. Position errors in pixels, are shown graphically on the computer screen. The Canon DSLR is then disconnected from MaxIm DL and connected to the ImagesPlus software program.

ImagesPlus then runs an automated multi-exposure imaging session which typically lasts for several hours. It is also used to download images from the DSLR and to set up the various camera setting.

From then on the imaging session requires no further human intervention. The Meade LX200GPS mount  follows the target image, getting guide corrections via its shared COM1 port, and the slit in the dome moves automatically every few minutes to maintain alignment with the telescope.