Attaching an Instrument to the WIYN 0.9-m Telescope

Marko Ristic
Rochester Institute of Technology
January 11, 2019

This is a compilation of pictures and notes taken during the attachment of the RIT Polarization Camera on the WIYN 0.9-m telescope in January, 2019.

The RIT Polarization Camera was the first external instrument to be attached to the telescope without substantial large-scale planning and coordination around the attachment of the instrument.

As such, these notes may be incomplete and may not necessarily represent the attachment of all types of instruments onto the telescope.

The purpose of these notes is to serve as a primer and general source of useful information for attaching instruments to the WIYN 0.9-m.

Ideally, these notes will serve as a comprehensive guide to attaching instruments to the WIYN 0.9-m telescope in the future.

Further expansion of these notes from others' experiences is welcomed and highly encouraged.

Instrument Attachment Pictures

Above is an image of the RIT polarization camera attached to the back of the filter-shutter assembly (FSA).

The four cardinal directions are identified relative to viewing the FSA from below.

Without the camera, the back of the FSA is exposed and the bolt holes are made apparent. There are five (5) holes arranged in a pentagonal pattern.

Note that the bolt hole pattern is NOT SYMMETRIC IN ALL DIRECTIONS - there is only symmetry along the axis (pink line) halving the pentagon.

Below is a drawing of the WIYN 0.9-m bolt hole pattern as well as a link to view and download the drawing.

• Click here to download WIYN 0.9-m Bolt Pattern Drawing PDF

Useful Measurements

Below are some images and notes which will provide potentially useful measurements for determining whether or not an instrument is suitable for the WIYN 0.9-m telescope.

The notebook introduced to the image of the bolt holes helps determine the size of the aperture in the FSA.

Each of the spaces in the binding of the notebook is 0.55 inches (1.4 cm) away from the next. There are roughly 9 spaces from one corner to the opposite corner of the aperture.

The aperture is approximately 5 inches (12.6 cm) from one corner to the opposite and houses 4-inch-by-4-inch (10cm-by-10cm) filters.

The distance from the back of the FSA to the CCD in the HDI is approximately 4 inches (10 cm).

At this distance from the FSA, the secondary mirror focuser sits roughly in the middle of its movement range.

The maximum focal distance from the FSA to the CCD is approximately 6.625 ± 0.5 inches (17 ± 1.3 cm).

This maximum distance was assumed by using the distance from the FSA to the RIT Polarization Camera and the resultant focuser position.

Distances from the FSA farther than this will NOT ALLOW THE SECONDARY MIRROR FOCUSER TO FOCUS ON THE CCD.

Distance from FSA	Focuser Position
4 inches	32700
6.625 inches	55000
Very rough approximation: 8500 focuser steps per inch distance from FSA

Important!

When the focuser is moved a given distance dx, the focal point moves a distance of 2dx; light from the primary has to travel an additional distance dx to reach the secondary and light from the secondary must travel another additional dx to reach the CCD, resulting in a total addition of 2dx to the total optical path length.

Each focuser step was found to be 0.5 μm, so each focuser step should result in the secondary mirror moving the optical path by 1 μm.

However, the approximation of 8500 focuser steps per inch (1 inch = 2.54 cm = 25400 μm) shows that the focuser has to move one-third the distance moved from the back of the FSA.

This discrepancy was noted, however its origin has not yet been identified as of the writing of these notes.

Helpful Tips

Finally, a list of helpful tips is included below, some of which have been discussed in further detail prior in the document.

• Telescope pointing is accurate, but it would be wise to bring some finding charts to verify positioning and orientation, especially if using an instrument with a small field of view.

• The maximum focal distance from the back plate of the filter-shutter assembly is 6.625 ± 0.5 inches (~ 17 ± 1.3 cm). Distances from the filter-shutter assembly farther than this will not allow the secondary mirror focuser to focus on the CCD.

• Use 1-inch or shorter bolts/screws for attaching the instrument to the back of the filter-shutter assembly. Bolts/screws longer than 1 inch pose the danger of damaging filters or the filter wheel.

• Remember to move telescope filters to empty if using personal filters.

• Open the CCD shutter on the telescope software - it does not open by default! Also remember to close it after your instrument has been taken off the telescope so that HDI can properly take bias frames.

• There is no power connection on the telescope itself it is supplied from the platform surrounding the telescope. Therefore, bring many extension cords and power strips! It would also be wise to bring cable ties to secure power strips and manage cables around the instrument/telescope.

• Bring a long ethernet cable (50 ft or longer) to connect the computer taking data to either a) a second laptop in the control room which will communicate via an ethernet connection or b) the router such that the machine has internet and can be remotely accessed (TeamViewer, etc...).

• Bring an external hard drive on which to save backup data.

It is highly encouraged that future observers who attach their own instruments on the 0.9-m revise and expand these notes for completion.

Please contact Michael Richmond or Marko Ristic for questions, concerns, or additions to the document.