Titan Mount at YFOS
YFOS is the New Hampshire Astronomical Society's dark sky site. We decided to buy a Losmandy Titan mount and I undertook the project of designing a pier. As we wanted to have the pier ready before the Titan arrived, I got a dimensioned sketch of the mount from Scott and used it as a design guide. I also made a mechanical drawing of the observatory and roll-off roof to ensure that the finished project would fit inside. I used 3-D CAD software called Solid Edge for all the designs.
The pier is made up of a steel base plate 24" in diameter by 2" thick. Welded to it is a 4' length of 10" schedule 40 steel pipe, topped with a 5/8" thick plate. As our roll-off roof observatory is not exactly aligned north-south, the offset is compensated for in the top plate, otherwise there would not be sufficient adjustment in the mount to achieve polar alignment. We chose to make our own adapter rather than order the MAL adapter Losmandy sells. The pier is filled with dry sand for vibration damping and the level of sand was adjusted to give the lowest center of gravity for the pier plus mount plus telescope. I used a composite design of the pier, mount and telescope that allowed me to calculate the center of gravity as a function of sand level using Solid Edge.
A mechanical drawing of the adapter and a photograph of the pier are shown. A complete set of mechanical drawings for the pier is available.
German Equatorial Mount Fuzzy Zone
In a typical GEM, there's an area around the Meridian that can be viewed with the telescope on either side of the pier. In Mel Bartel's ScopeI program, this is referred to as a Fuzzy Zone. In the original implementation, a single parameter was defined resulting in a zone that was equal on both sides of the Meridian. Several people on the Yahoo scope-drive group suggested the need for an asymmetric Fuzzy Zone so I undertook writing the software to support it.
While a Fuzzy Zone is one where the telescope can go beyond the Meridian, by setting the parameter negative, you can also define a Safety Zone where the telescope can't get to the Meridian. One of the problems I encountered in designing the code was visualizing what was happening. The telescope drive input parameters are concerned with where the telescope is pointing, but the Fuzzy and Safety Zones are concerned with where the bottom end of the telescope is going.
The following is a discussion of the Asymmetric Fuzzy Zone parameters and some diagrams to help illustrate the various situations.
Polar Alignment of an Equatorial Mount
I've spent a good deal of time over the past several years working on this problem. While the traditional method of drift alignment is well documented and produces excellent results, it takes some time to get good alignment. This is fine for a permanent installation, but for the observer with a portable setup, any time taken aligning the mount is time taken away from observing.
One can always treat an equatorial mount as an alt/az mount with the azimuth axis tipped well away from vertical and do a classical two-star initialization. However, unless the mount was fairly close to polar alignment to start with, photography will be compromised and all the advantages of an equatorial mount will be lost.
What I was looking for was a computer algorithm that would take the results from a two-star initialization and use them to assist in the alignment process rather than using the results to convert from the mount's reference frame to the polar reference frame.
The following is a monograph that details the solution. The algorithms have been implement in Mel Bartel's ScopeI software.
Nikon CPU Lens Adapters
Many of the Nikon Nikkor lenses contain a PROM chip that gives the camera lens information such as focal length, f-number, etc. If this chip is missing, light metering in the camera is turned off requiring the user to quess at shutter speed and/or f-number to get the correct exposure.
There are several sources for adapters to couple a camera to a telescope, but the camera needs to be used in Manual Mode, quessing at the shutter speed to get the correct exposure. For stationary objects there is time to take several shots to bracket the exposure, but for dynamic shots a critical scene may be lost. Following are descriptions of adapters I made to integrate Nikkor PROM chips with telescope-to-camera adapters.
Prime Focus 2" Adapter
Turning the mounting plate over, you will see a lever that is used to control the lens aperture. This should be removed. In the photograph you can see the flexible circuit containing the PROM.
The plastic ring used to manually set lens aperture can be lifted off the lens. We need this as it has a small tab on one side that closes a switch on the camera to indicate the aperture ring is locked. On the opposite side you will find a small ridge that should be cut off using a sharp knife. This will provide a smooth surface to mount the ring to the adapter. The wide horizonal tab should not be removed. In the lens it is used to limit the movement of the ring but we will use it to hold the ring rigid in the adapter.
I purchased a damaged Nikkor 24mm f/2.8 lens and disassembled it to retrieve the pieces needed. The mounting ring is fastened to the lens by three screws. Removing them allows you to remove the entire end of the lens, including the PROM contacts and the circuitry.
Note the orientation of the plastic tab to the left of the screwdriver relative to the contacts. You must maintain this same orientation when assembling the adapter.
If you have metric taps, the screws should be saved, otherwise 2-56 screws can be used. Make sure the heads are small enough to fit into the recesses in the mounting ring.
Pictured are the four parts that make up the adapter. The 2" barrel is from an Orion prime focus adapter, but this could be made from a brass or aluminum tube. It screws into the adapter with 24TPI threads.
The finished adapter
This photo shows the ring fitted to the adapter which is machined from either a piece of 1/2" plate or same 2-1/2" round stock.
Note the slot in the adapter that holds the wide tab on the plastic ring. This should be machined prior to drilling and tapping the three mounting holes so the location of the hole on the same radius as the small tab can be set.
The mounting holes are on a 26mm/1.024" radius.
Eyepiece Projection Adapter
The Meade adapter I owned already had a Nikon bayonet mount so I just needed the PROM circuitry. In this case, the circuity from an AF-G lens was the best choice as these lenses have no aperature ring so no external parts need to be added to the adapter.
I acquired a damaged 28-80mm 3.3-5.6G zoom lens and disassembled it to remove the entire PROM flex mounted circuit. Also saved was the light baffle that mounts to the adapter ring. This is used to mount the PROM circuit in the finished adapter.
NOTE
Some Nikon zoom lenses have the PROM circuit mounted on a
hard board. These would be much more difficult to integrate.
This is the PROM circuit with the camera contacts. The contact strip to the right reads the lens's focal length information while the contract strip below reads the focal distance. Both can be cut off as the information they read can be ignored.
This is the camera adapter with the PROM circuity mounted using double sided tape. I glued an HDPE 35mm film can to the baffle using JB Weld. As HDPE is notoriously difficult to glue, I drilled holes around the end and allowed the epoxy to extrude through the holes to give a gripping action.
This is the assembled adapter showing the mounted baffle. In some Nikon lenses, the baffle is attached by screws that thread axially. As bayonet rings for prime focus and other adapters don't have an inside flange to mount to, baffles that attach with radial screws are needed.
The finished adapter
