This is a telescope designed specifically for video occultation measurements. It has large aperture and small f/ratio, and internal video camera with no eyepiece option. It uses two types of video cameras: an NTSC (analog) security camera, PC164C-EX2, and a USB video camera, Lumenera SKYnyx2-0m. An essential part of occultation timing is accurate timestamps on the video, and this is provided by a gps-based reference signal with microsecond accuracy. The analog camera uses a KIWI video timestamp, while the USB camera uses a custom designed optical timestamp slaved to the GPS pulses.
This telescope was designed to be simple to construct and robust for rapid setup in the field. Here are the design goals:
- Large aperture, small f/ratio, and manageable weight
- Compact enough to fit easily in a sedan, and use on a mid-range equatorial mount
- No need for eyepiece and no concern for tube currents since all work is at low magnification
- Easily manufactured with simple home tools: table saw, router, etc. No need for machine shop tools.
- Rigid but lightweight construction that holds collimation around the sky
- Light enough to load onto mid-range equatorial mount
- 10" f/3.6 design, also allowing f/1.8 with 0.5x focal reducer
Occultoscope mounted on CGE, with dust covers in place. You can see the simple wingnuts and slots that provide focus. When a focal reducer is used, fine focus can be made by rotation of the focal reducer in its threads.
Layout of internal components, all from 1/2" poplar plywood. The mirror cell is a doubled piece of the plywood. The two other circular apertures serve as baffles and structural reinforcement. Using f/3.6 rather than f/4 allowed the entire construction with a single 4x8' sheet of plywood, and makes it easier to fit in a small sedan
View of the Lumenera USB video camera at prime focus. Although it looks large, it is not much bigger than a secondary mirror, and such a mirror would have additional losses from the added reflection. The camera brackets are made from easily cut pieces available from home supply stores and do not require any special machining
PC164C-EX2 video camera on holder. Note how little obscuration there is from this small camera, and it is quite sensitive. Its disadvantage is the lack of frame rate control, lack of linearity, and analog rather than digital USB signal. You also need some sort of video2usb converter to record directly to disk rather than to a camcorder
Rear view showing the mirror cell (Parks) and Telrad. No attempt was made to improve air flow since the intended usage is at low magnification, and the 'scope is expected to be pre-equilibrated thermally. The mirror is from a full thickness Pyrex blank. The priority here is to stop light leaks from the outside. The mirror was custom figured by Squirrel Trap Optics. Three wires emerge through the rear cell: ntsc video, USB video, and the light source for the optical timestamp device. One additional wire is needed to provide power to the ntsc camera, but the usb camera is powered directly by usb
Occultation and Video Timing Projects
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