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Home --> Telescopes --> 6 inch Dob --> Filter slide and mirror cell
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| The filter slide before painting and assembly. | The finished filter slide. |
I have a deep sky filter and an oxygen III filter. It's a hassle screwing and unscrewing filters to each eyepiece; plus, my filter are 2" diameter, so they aren't compatible with my 1 1/4" eyepieces. With a filter slide, I expect to use the filters a lot more often since they are always ready for use. The filter slide fits inside the tube beneath the focuser, and is held in place by three fixed screws. One issue was the focuser: it is made so the focuser tube can extend as far as an inch into the telescope tube, which would be incompatible with the filter slide; consequently, I used wood spacers between the focuser and the telescope tube so the focuser barely protrudes into the telescope tube even in its lowest position. The filter slide is held in place by friction alone, and can easily be pulled out of the telescope; however, I find it convenient to just leave it in the telescope and store my filters there.
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| The circular disk for the back of the telescope, to which the mirror cell is attached. This arrangement allows an electrical connection from the batteries to the fan without any dangling wires or plugs to connect. |
These days many home build telescopes have at least one fan behind or near the primary mirror. This speeds up the process of cooling the mirror and tube interior to the ambient air temperature. I bought a 5 volt fan from an online electronics supplier, as well as a battery holder and switch. The battery holder and switch are attached to the tube near the lower end. The fan is attached to the mirror cell, so I needed some way wire the batteries to the fan. I didn't like the idea of having to manually plug or unplug the wiring whenever I remove or attach the mirror cell - too risky. So I assembled the electrical contacts shown in the picture. This way there are no wires or plugs to deal with when I attach or remove the mirror cell from the telescope. The springy electrical contacts are cut from a U-shaped spring made to hold photographs in a frame.