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4. AP155 automated focusing assembly (Robofocus)
5.AP155 Star spike mask (home made - really cool results!)
7. Focusing arrangement on the FSQ106N
8. Radio link from observatory to house for remote control
9. Ritchey-Chretien RC400 Equipment
10. Software control systems used
The mounting pillar is custom made from welded steel. The intention was to create usable space inside the pillar to accommode the cables and power supplies. There are two steel sheves inside that support the AC to 12VDC transformer for the AP 1200GTO mount, the AC to 12VDC transformer for the CCD camera assembly and a separate set of 12VDC regulated connection sockets for other accessories. The transformer for this regulated supply is beneath the computer desk behind the left hand front wall in this photo. All the shelves, top flange and base flange of the pier have 40mm diameter holes in the centre to allow the free run of plugs and cables. The pillar has a 600mm square flange welded to the base. This flange is bolted down onto a 1 cubic metre concrete block set into the ground. Around this block the concrete base of the building is 150mm thick.
Power cables are routed under the wooden panelled floor to a fused distribution box on the observatory wall. Operational cables for the PC to mount and accessories are routed under the floor in the opposite direction to avoid interference. The floor is raised 25mm off the concrete base by wooden slats to reduce vibration in the mount and to raise the floor above the rainfall level outside.
The mount control electronics and hand control are currently on the chip kit "D". The only problem I have ever encountered with the mount is the physical connection of the 12VDC input jack. This needed to be tightened with pliers to avoid intermittent bad connection and the resulting loss of power.
With the risk of snagging and the inherent weight of the cabling needed to operate the focuser, camera and heater or cooler it was important to keep them tidy. However it is important to ensure that pulsing power supplies such as for a Kendrick dew remover or raw AC power are kept away from data cables as these can cause interference and data corruption. The rest were placed inside a cable tidy shown in the photo and this was loosely hung onto the mid-section of the scope or the mounting plate to enable freedom of movement of the telescope to any position.. This detail can seriously affect your financial health and imaging results and should not be ignored. On a couple of occasions the mount has set off to park and lost its bearings (due to my error) resulting in the whole cable assembly getting jammed between the telescope mounting plate and the fixed mount. This was very bad news!! Fortunately, no damage was done but it could have damaged the drive electronics.
Incidentally, the spare cable you can see running over the floor is a serial cable I was using to test out PulseGuide. This is not now used and has been removed.
When taking digital images of faint objects, it is important to get rid of the subtle variations in the distribution of light in the optical system. This is called Flat Field processing and involves taking a set of exposures of an evenly illuminated field with exactly the same, unmoved, camera and telescope setup that was used for taking the astronomical images. This will allow the effects of light obstruction in the optical path (vignetting), dust specks on the optics and filters and internal reflections (hot spots) to be removed from the final images. To achieve this I use a light box that provides an evenly illuminated white field at the front of the telescope.
The light box is mounted on the observatory wall so that when the telescope is parked after an imaging session, the flat fields can be taken immediately by pulling the light box out on its extending swivel and covering the front end of the telescope. The flat field images can then be taken and saved in the same imaging files as the astronomical images for later processing. The positioning of the light box is shown in the picture below.
The light box is mounted on an extended TV wall bracket and it sits unfixed on the TV support plate. This allows the box to be easily moved forward onto the front of the parked telescope. The power to the light box is from a variable (by switch) wall socket transformer giving 1.5, 3.0, 4.5, 6.0, 9.0 and 12VDC outputs. The box is made from artist's foam filled card with a 9mm plywood front face.
Inside the box and set around but shielded from the Acrylic screen are four white LED's linked in parallel to the power socket mounted on the front face. I use these LED's with the 3VDC switch from the transformer to achieve around 25,000 ADU level of illumination in 10 second exposures on my ST-2000XM CCD camera. There is no other form of baffling inside the light box and it works fine with the setup I have.
The AP155 refractor was first fitted wth the Astro-Physics RoboFocus Bracket. This is an inexpensive but neat and rigid method of fitting the stepper motor of the RoboFocus to the rack-and-pinion shaft of the AP155 focuser assembly. The instructions for fitting are supplied with the bracket kit and the bracket is made with the correct sized slots for the RoboFocus supplied nuts and bolts. This only involves the removal of one of the AP155 focuser knobs and slipping the clutch collar over the exposed shaft. The photo below shows the assembly.
When the RoboFocus has been fitted the clutch collar grub screws are tightened on to the rack-and-pinion shaft and the stepper motor shaft. This clutch pressure on the rack-and-pinion shaft is easily capable of supporting the camera assembly without slippage. To demonstrate how well engineered the Robofocus is, I show below the current load that it is supporting - in excess of 10 pounds weight. This is the AP Field Flattener, The SBIG ST-11000M CCD Camera and the SBIG ST-L (an 8 position x 2" filter wheel unit).
This mask is used on the AP155 refractor to create the traditional star spikes (diffraction spikes) of type that appear on systems that use secondary mirror supports. It took 30 minutes to make from a sheet of 1mm thick textured black plastic sheeting available from any signmaker and some dressmakers black elastic. The only tools needed were a cutting knife, cutting mat and some superglue. The total cost was under £1.50 ($3 at todays exchange rate)
The circular cut-out on which the diffraction cross-hair was mounted was made from a piece of plastic sheet 200mm square.The hole diameter is the inside dimension of the dew shield on the AP155. The cross-hair itself was made from 1mm diameter fine black elastic used by dressmakers. The cross-hair was located into 1mm wide slots cut into each corner of the square. The webbed brackets were cut from the same plastic sheet and superglued to the mask at 90° intervals. Both the brackets and the mask were slotted to help strengthen the joint and each of the brackets were set back from the rim of the mask aperture by just the thickness of the dew shield - about 1.5 mm. This prevented the mask from slipping in to the aperture but positioned the mask itself exactly central on the dew shield. The brackets were all drilled out with holes in the same position to allow another piece of black elastic to run through them.
The elastic cord shown passing through the bracket holes in the above picture fits around the AP155 dew shield and holds the whole assembly comfortably in place.
The final trick was to place the mask on the scope at the preferred position of the spikes relative to the CCD X-Y axes and place just one pair of insulating tape strips snugly on either side of the bracket but on the dewshield surface only. I was surprised that this simple method holds the mask firmly in the same position yet the mask can be repeatedly removed and replaced with exact repeatabiliy on the dewshield. Obviously, if the dewshield is taken off and then replaced on the telescope, then this will not repeat the positioning exactly relative to the telescope. The picture below shows the spike generator in place on the AP155 dew shield.
The Takahashi was mounted onto the AP155 tube rings using (a) AP mounting plate compatible hinged tube rings from Parallax (b) Home made aluminium spacer blocks to raise the Tak an extra 20mm clear of the AP155 (c) AP Losmandy sliding bar. The Losmandy plate into which the sliding bar was set was bolted to the top of the two AP155 tube rings.
A RoboFocus stepping motor was attached to the Takahashi rack and pinion mount as shown in the second picture above. One of the focusing knobs was removed and a collar was supplied with the motor to fit the FSQ106N shaft exactly. The AP155 also has the RoboFocus motor setup and the same controller is used when imaging with one or the other of the Tak or the AP155 (or the Newtonian when it replaces the whole of this scope assembly from time to time).
The observatory PC is controlled directly from the keyboard/mouse below the shelf in this picture. However, once the observatory has been opened and (if necessary) the telescope re-synchronised on a star, a PC is used in the (warmth of the) house to take over control of the observatory PC. I have now chosen to use RADMIN for this remote PC control as it is secure, fast and easy to manage. It is also well supported by AVG Internet Security, which is the firewall and virus protection system that I use.
I use a Buffalo 54 Mb/s PC card in the observatory and a Belkin Wireless Pre-N Router in the house. The radio standard used is 802.11g and the configuration I use is a simple Peer-to-Peer link. To achieve a real life data rate of around 11 - 20 Mb/s a higher gain aeriel is needed in the observatory. Without this the data rate falls to 5 - 11 Mb/s.
In the first picture, the PC and the web controlled mains power switch can be seen in the D.I.Y cabinet. The 19" widescreen monitor is sat on top but this is always switched off except when performing tests and maintenance so as not to throw light into the path of the telescope. The Paramount telescope mount has been roughly aligned and the main cables have been installed and are ready to connect to the various devices on the telescope when it is bolted to the mounting plate.
In the first picture, the PC and the web controlled mains power switch can be seen in the D.I.Y cabinet. The 19" widescreen monitor is sat on top but this is always switched off except when performing tests and maintenance so as not to throw light into the path of the telescope. The Paramount telescope mount has been roughly aligned and the main cables have been installed and are ready to connect to the various devices on the telescope when it is bolted to the mounting plate.
In the second picture, the RC400 has been bolted to the mounting plate and the black anodised rear cell plate can be seen with the integrated controller for the primary and secondary mirror dew heater controls and the primary mirror cooling fans. However, in the climate of New Mexico, the dew heaters are not required. The black focusing device is attached to the rear cell plate. This is a Strlight Instruments FTF 3545 electronic focuser - 3.5" inside clear diameter. Inside this focuser the AstroTech Field Flattener lens is mounted which corrects the prime focus field such that it is flat across a 45 mm diagonal imaging chip. The red anodised device attached to the focuser is an Optec Pyxis 3.5" Rotator which allows the whole of the camera and filter assembly to rotate by remote control. This allows the object that is being imaged to be framed in the optimum way and/or a suitable guide star to be located for all imaging sessions. The camera and filter wheel are attached to the focuser. The camera is the SBIG ST-11000M anti-blooming 11 Mpxl monochrome CCD camera with an integrated ST-237 guide CCD chip. The filter wheel unit is the SBIG FW-8L with eight positions for filters. It is set up with Luminance, Red, Green, Blue, Clear, Hydrogen-alpha, Oxygen-III and Sulphur-II filters.
The third image is a close-up of the very rugged and high quality FTF 3545 focuser and its electronic drive.
10. Software Systems
The following sofware systems are used on the observatory PC. The PC's operating system is Windows XP Pro. The indoor laptop operating system is Windows XP Home.
Telescope positioning - TheSky planetarium software V6.00.60
Camera control - MaxIm DL version 4.53 or CCDSoft V5.00.1186
Image acquisition - MaxIm DL version 4.53 or CCDSoft V5.00.186
Focusing system - Robofocus/FocusMax V3.2.6
Mount alignment - Star drift on imaging CCD and TPoint
Periodic error correction - PEMPro
Telescope Control (whilst imaging) - TheSky, MaxIm DL or CCDSoft
Image processing - CCDStack, Registar and PhotoShop CS
Remote PC control - RADMIN