This is the new Pommier Observatory. It consists of a 10’6” diameter Ash Dome on a supporting structure building. I absolutely love this new dome. It is the real thing! It has independent upper and lower shutters. The lower shutter covers the sky from the horizon up to 30 degrees above the horizon and I will rarely image things in that part of the sky. Therefore, I can leave the lower shutter closed and it greatly reduces stray ambient light in the dome. The shutter motors are quiet and the dome rotation motor is very quiet. The door is below the dome and I can enter and leave as often as I want without interrupting imaging. The dome electronics keep the dome slot centered on the telescope’s position and updates every few seconds, so it tracks my targets across the sky flawlessly. An enormous advantage of a dome observatory compared to a roll off roof observatory is protection from the wind. Wind will not enter the dome through the dome slot, simply because it has no exit. So the telescope remains rock steady for imaging even on the windiest of nights. Wind can still hit a telescope in a roll off roof observatory and shake it, leading to jiggly stars. Also, wind hits a flat wall of a roll off roof observatory and creates turbulence that spills over the telescope, degrading seeing conditions. In contrast, wind will flow smoothly around the curved surfaces of a dome observatory maintaining better seeing conditions.
The new imaging system in the new Pommier Observatory is a PlaneWave CDK400 system. A CDK 400 system consists of a CDK17 (17-inch) telescope mounted on an L500 mount.
The CDK17 is a fantastic telescope. It is fast, at f/6.8. The optics are truly superb. It produces a completely flat field with stunning clarity and pinpoint stars from corner to corner of my 35 mm CCD chip. It has a fused silica mirror and carbon fiber trusses that resist expansion and contraction and hold sharp focus throughout the night regardless of how much the ambient temperature changes. The CDK17 has many built in fans that help it reach ambient temperature quickly and blow air across the primary mirror surface to remove the boundary layer of air that can blur images. I added several accessories to the CDK17, like the IRF90 rotator/focuser, the Electronic Focuser Accessory, and the Delta-T Heater dew control system. See those pages for details on them.
The L500 is an equally amazing mount. It is direct drive, so it has no gears and therefore no periodic error and no backlash. Once it builds a pointing model, it precisely center targets on the CCD chip. It tracks flawlessly for long periods of time. Although I usually still autoguide when there is a suitable guide star (see page on the IRF90), I can also now image subjects with no available guides star by just letting the L500 run all by itself and I still get perfectly round stars even with long sub-exposures. This enables me to image subjects I never could with my Compustar C14 due to lack of a suitable guide star. The L500 has through the mount cabling to prevent cable wrap.
The PlaneWave CDK400 system is mounted on a massive concrete pier. The pier is 30” in diameter and rises 4.5 feet above the observatory floor in order to put the intersection of the right ascension and declination axes of the L500 mount at the center of the 10’6” Ash Dome. This massive pier is necessary to handle to torques of the L500 direct drive mount. The cylindrical portion of the pier above ground weighs about 1 ton and there is an equal amount of concrete in the ground as a rectangular footing with a cylindrical projection into the ground beneath that to prevent the pier from leaning over time. The pier is extremely stable. I can open and close the observatory door, walk around on the observatory deck, and the dome motors can rotate the dome to update the alignment of the dome slot with the telescope aperture, all without jiggling the telescope/mount and ruining a sub-exposure.
I added the IRF90 Integrated Focuser/Rotator to my CDK17 telescope. Combining this with the PlaneWave Electronic Focuser Assembly (EFA) allows it to automatically obtain pinpoint focus. It takes a series of 5 images at different focal points, analyzes the stars in the image for their full width-half maximum (FWHM), then plots a parabolic curve of focal position vs. FWHM and determines where on the curve is the optimal focus. It then sets the focus to that position. It nails pinpoint focus every time. It can be programmed to check focus at pre-defined time intervals throughout the night. However, the fused silica mirror and carbon fiber truss construction of the optical tube actually hold that focus all night long and I have yet to encounter an instance in which it adjusted the focus.
The rotator rotates the camera to any position angle to compose my images and acquire the best possible guide star. It has an accuracy of 1/1000th of a degree, so I can precisely reproduce the rotation angle of the camera if I come back to acquire more data on any given target or to shoot flats just as they would have been on the night the images were acquired.
I added the PlaneWave Delta T Heater System to my CDK400 System. The CDK 17 has ambient temperature sensors, temperature sensors on the primary mirror backplate, the primary mirror, and the secondary mirror. Those components are also pre-wired with electronic heating elements. The Delta T system monitors the temperature of all these components and if the difference between them and ambient temperature is such that the optics are in danger of forming dew, it will activate the heating elements and keep them dew-free. The CDK 17 also has a large number of fans that help it reach ambient temperature rapidly and can remove the boundary layer of air on the primary mirror that can distort images.
The PlaneWave L500 mount is mounted equatorially on the observatory pier via a PlaneWave Wedge. The Wedge is attached to a PlaneWave Pier Adaptor Plate, which is bolted to the concrete pier. The wedge has adjustment bolts that allow the polar alignment to be adjusted +/- three degrees in both azimuth and altitude. The PlaneWave Pointing Model software will plate solve images and determine the error in the polar alignment and advise how many turns of the azimuth and altitude adjustment knobs are needed to achieve better polar alignment. After that, the Pointing Model will compensate out virtually all errors and the L500 will beautifully center targets. Of course, with a fork mount, no pier flips are ever required.
The imaging camera is an SBIG STL 11000M CCD camera. It has a CCD chip containing 11 million 9 micron pixels with the same dimensions as a 35mm film frame. Personally, I still prefer the aspect ratio of a 35mm film frame for my images compared to the square images with the 16000 chips in other cameras. The STL 11000 is a self-guiding camera with a built in separate guide chip for autoguiding. It also has a built in 5-position filter wheel in which I have Baader Planetarium L, R, G, B and H-alpha filters.
This is the Electronic Focus Accessory (EFA) I added to the CDK17. It controls the IRF90 focuser/rotator. See the page on the IFR90 for details on its operation and capabilities.
The EFA has a plug-in hand controller, pictured in the inset at lower left, that permits adjustment of focus and rotation when the telescope is being used visually. The rate of focus change or of rotation change can be adjusted by the Rate button on the hand controller. The hand controller can be clipped to the rear plate of the telescope when not in use.
