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Sky Camera using the Raspberry Pi
Designed by Mark Little
 
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If you are not using a fish eye lens, then a dome cover may not be necessary and it may be possible to use a cheaper camera case like the one shown on the left. While this case is cheaper than the dome camera housing, it has the disadvantage that it does not protect the camera lens and the Printed Circuit Board (PCB) behind it from rain or fog.

A simple means of protecting the camera would be to fix a piece of glass in front on the hole for the camera. The glass used would need to be free of any optical imperfections that would distort the scene being viewed by the camera.
If working with a fisheye lens, then you will need to protect your camera from the direct Sun and provide a dome cover for the upwards pointing camera. A typical transparent dome can be seen in the image to the right. Depending on the dimensions of the camera mount, it may  be possible to use a ready made housing.
To see the options that are available, search for "Transparent Dome Cover" and "weatherproof dome camera housing". For Australian constructors, a weatherproof dome camera housing is available from Jaycar (although it is currently a discontinued line). It should be noted that fisheye lens will need a clear dome and domes with dark strips on either side of the dome may block the image. Ensure that these strips can be removed if there is a chance it will block the camera's view.
When protecting your camera from the direct Sun, remember that the Sun not only moves From East to West each day, it also moves North and South as the seasons change. The two-axes of Sun movement complicates the blocking out the Sun an dout of scope for this article.
To prevent moisture and/or contaminants from getting into the case, the perimeter of the glass should be completely sealed with something like Silastic™ which would act as both an adhesive and a moisture barrier.
The glass would be attached to case front and sealed before the camera is installed, just in case any fumes from the curing of the Silastic has a detrimental effect on the camera optics of Printed Circuit Board (PCB) - better to be safe than sorry!

No matter what your mounting method, you can be assured that dust and grime will accumulate on the cover, as will occasional sprinkling of bird droppings. For this reason, it is important that the mounting location for your camera is easily accessible to allow cleaning.
Next
The Raspberry Pi is capable of interfacing with a video camera via a 15-pin ribbon cable, or via its Ethernet connection. This project deal with using the camera interfaced by the ribbon cable.

Before starting, it should be noted that the cameras commonly available for the Raspberry Pi do not have wide angle lens as are often seen on sky cameras as shown in the image to the left.
It is, however, possible to procure camera which do have a wide angle lens that is more suitable for sky cameras. A Google-search for "Raspberry Pi wide angle fish eye camera" will definitely bring up a selection of suitable cameras. Of course, if you are happy with a smaller area of coverage, then the more standard camera lens configurations will also work.