Telescope auxiliary systems


Filter Wheel

The Filter Wheel and guider were both manufactured by Astronomical Consultants and Equipment of Tucson, Arizona. Their phone number is: (520) 579-0698. There is a manual written by the Filter Wheel and Guider's designer, Dr. Peter Mack.

One issue with the guider is that, since it is on the rotator, there are cable wrap issues. Since we do not have an ideal solution, the cables may occasionally go bad at the connectors. All of the cables use AMP connectors, which use crimp pins. These can be ordered from a variety of electronics sources, e.g. Digi-key corp: the AMP part numbers for the pins are 1-66103-7 and 1-66105-8. There is a crimp tool in the 1m tool box that allows one to attach wires securely, and another tool for removing pins from their sockets.

The Filter Wheel Housing consists of a removable/interchangeable wheel, four small switches that encode position information, a detent lock that holds the filter in a given position this detent lock is driven by a motor and has three separate switches to sense its position and a rotation motor. All of the switches are simple microswitches that may be ordered from an electronics catalog. Details about the operation of most of these components is in the Guider manual.

There are replacements for both of the motors of the Filter Wheel on the top shelf in the 1- meter control room at Apache Point.

The most complicated part of the Filter Wheel has to do with the Detent switches. Two of the switches surround the Detent motor cam shaft. Of these, the lower most senses when the Detent is completely disengaged. The upper most senses when the Detent is up, but not necessarily engaged in the filter wheel. The final switch is on the opposite side of the filter wheel, near the Detent spring. This switch is activated when the Detent fully engages in the filter wheel. When this final switch is engaged, the filter wheel is said to be "home."

The filter wheel operates as follows: The detent is disengaged. The filter wheel is commanded to run most of the way to the final position. The detent is run in. At this point, the detent is not necessarily engaged. A "run-until-home" command is executed. When the detent engages, the filter is home. The four "encoder" switches are then read to determine whether the filter moved to the correct position. Note, unless the filter wheel is "home" the encoder switches will not necessarily read the correct position. One can get a combination of switches when the detent is not engaged that will give a false reading. How the filter encoder switches work is described in detail in the Guider Manual.

To troubleshoot the filter wheel box, it may be run while detached from the telescope. To do this, remove the top of the filter wheel and take the filter wheel out as described in the "Filters" section of this manual. The main body of the filter wheel box may be removed from its cover by removing the bolts around the perimeter of the filter wheel. The cover stays mounted to the guider module on the telescope. The filter wheel may be reinstalled without the cover plate. It slides in as described in the "Filters" section. Place the top on the filter wheel box. Once you plug the filter wheel back into the control cables, you will be able to run the filter wheel as though it were on the telescope. However, you will be able to see the operation of all the switches and motors.

There are two filter wheels that may be used. One is a ten-position wheel for 2"X2" filters. The other is a six-position wheel for 3"X3" filters.

We had problems with the triggering of the "detent out" switch in the summer of 2011. This was eventually fixed by adjusting an allen screw in the box that triggered the switch. In the process of diagnosing this, Ed Leon documented how the circuitry worked; his diagram can be found in FilterWheelDetent.pdf.


Filters for the 1-meter are located on the Filter Shelf in the 1-meter control room. This filter shelf is the lower most shelf above the computer "Loki." There are three sets of filters available for use on the 1-meter: 1) A Johnson broadband set, 2) A Gunn broadband set, and 3) A narrowband set owned by Dr. René Walterbos. The Johnson and Gunn sets are NMSU property and may be used freely in the 1-meter. The Walterbos narrowband filters may be used in the 1-meter as long as he does not have a priority project on another telescope. Dr. Walterbos' filters are stored in a filter box. The combination to this box is 656.

An SDSS set of filters was purchased from Custom Scientific.

The original UBVRI set of filters was damaged spring 2013 and had shown degradation for some time before that. A new set of UBVRI filters was purchased at that time from Astrodon.

Great care should always be taken in the handling of filters. Only hold them by the edge. Remember that filters are very fragile. Do not drop them. Avoid getting fingerprints on the filters. The filters will need periodic cleaning even with careful handling. Use canned air to gently blow filters free of dust. Dust blowing is the most commonly required cleaning action. In the event that something more difficult to clean off gets on the filter, there is a filter cleaning kit on the Filter shelf in the 1-meter control room. The kit contains solvents for gentle cleaning of the filters. Use only lint free wipes or medical grade cotton to wipe the filters.

There is hardware for installing filters in the filter wheel on the Filter shelf in the 1-meter control room.

To install/remove filters:


As noted above, the Guider was built by Astronomical Consultants and Equipment of Tucson, Arizona. They can help with obtaining spare motors or other parts that might have failed. The cabling is documented in the Filter Wheel and Guider manual as noted above. Note this box uses motor controllers Applied Motion Products 3540M

The guider module is a self-contained unit that may be entirely removed from the telescope. This is useful when diagnosing problems. There are two stages the first is a radial (X) stage for positioning the camera in the telescope field of view. The second is a focus (Y) stage that moves the pick-off mirror further from and closer to the guide camera. Note the focus mirror does have the effect of acting like a radial stage.

One issue with the guider is that it is wired such that the limit switches are recorder tripped if the limit circuit is open. This means that in the case of connection/wire failure, the limits will read open and the stage will not move. So if the stage is not moving, it's a good idea to check the limit circuitry/wiring.

Another issue is that occasionally on the focus stage, the gears become disengaged.

Some notes about the guider:

Filter/guider wiring redesign, July 08

Six cables from telescope:

Mirror Covers

MIRROR COVERS ARE CURRENTLY NOT IMPLEMENTED. The old system, described below, was too unreliable.

Mechanical drawings of the mirror covers along with electrical drawings are in The Blue Notebook. There are six mirror cover motors. They are Pittman motors, part number GM9413-5 and are available from Automation Solutions in Englewood, Colorado; phone number (303) 792-5518.

When operating the mirror covers, the telescope must always be near vertical. To open the mirror covers manually: There are three switches on the TCS box on the left-hand side of the rack in the dome. Flip the left-most to manual control. Flip the middle switch to "Set 1" Hold the "Open" switch up until the covers stop moving.

To close the mirror covers manually: As above, make sure the left-most switch is in the manual control position. Flip the middle switch to "Set 2." Hold the "Close" switch down until the covers stop moving.

The "Set1"/"Set 2" switches refer to which set of limit switches (i.e. the open or close set) are active and determine the order in which power is applied to the mirror cover motors. "Set 1" is for "open" and "Set 2" is for "close."

To move the mirror covers via computer, make sure to leave the left-most switch in "Computer Control."

There are two possible weak points in the mirror cover design. 1) The motors themselves may be right at the torque limit. New motors should be investigated and identified to replace those that are currently in place. 2) The mirror covers have a rigid coupling between the motor and the covers themselves. Perhaps this should be replaced with either a flex coupling or a slip coupling of some sort.

Occasionally, the bottom two mirror covers don't seem to close completely. This is easily remedied by loosening the set screws in the motor shaft-couplings and gently pushing the covers all the way closed. Re-tighten the set screws. This should be checked about every two weeks.

The most common failure mode with the mirror covers is damage to the gear head due either to the torque problem mentioned above or mirror cover collision. If the mirror covers fail, loosen the set screw that holds the mirror cover to the motor on each mirror cover panel. At this point, the mirror cover panels will be free to swing open. Open the mirror covers in the correct order A panels first, B second and C third. Re-tighten the set screws that hold the mirror cover panels to the motor shaft. If a given mirror cover panel will not remain open, strap it open using duct tape or cable ties. Replace the damaged motor.

Some possibly useful information if one wanted to redesign the mirror covers: the mirror cover central rest is about 17 inches diameter. The tertiary baffle is about 16 inches diameter and extends upward starting about 5 inches above the central rest.