Mirror box and Mirror cell

My first mirror boxes had the usual open structure. Nowadays I also use a multiplex board as bottom. Why is that? Doesn’t it make it for instance all very heavy? Yes, indeed, and that’s exactly what I want. By making the mirror box rather heavy, I can keep it shallow. This has the advantage that it can be combined with a lower and thus lighter rocker box. This combination is also very sturdy and stable. It also keeps the sides solidly in place, no extra wood is needed to reinforce the sides. The best example of how this worked out can be seen with the 16-inch telescope (picture below).

I kept the 16-inch mirror box heavy, but no more than 26 cm tall, and placed a 12 Volt battery (that fuels the fans) in it for extra weight.

Mirror cell
To the bottom plate of the mirror box I attach the mirror cell, which is unusual, but has to do with the way I collimate the primary mirror. I don't like it much to kneel behind the telescope to adjust the collimation bolts, get up every time to see how the donut of the barlowed laser at the focuser shifts a bit, get down again and so forth. If possible, I want to collimate the primary mirror while looking at the same time at the returning laser light at the focuser.

The trick to achieve that is to move the entire mirror cell plus mirror up and down with large bolts that I twist from above. There are three large collimation bolts that go through both the ground plate and the mirror cell. A large ebonite knob is attached to the top of each bolt, for easy turning while collimating (below, left). The bolt first goes through a long nut that is glued into the metal of the mirror cell (below, middle). Then, the bolt goes through another, similar large nut that traverses the bottom plate of the mirror box, but this one is not glued in the bottom plate of the mirror box. Instead, two other nuts, above and under the bottom plate, just prevent this long nut from moving up and down (below, right). Now, when you twist one of the ebonite knobs, the entire mirror cell and the mirror will move up or down with respect to the bottom plate. And this is your collimation of the primary mirror! It is very easy to perform while you look at the laser light returning to the focuser. This collimation system turns out to be very stable. Whether you point the telescope to zenith or to the horizon, the barlowed laser donut at the focuser moves only very slightly, and this is the case during the entire observation session.

Another advantage of this mirror cell design is the mirror support. The mirror rests against two roller skate wheels, which each can rotate freely in a solid piece of aluminum that are screwed to the mirror cell, while making an angle of 90 degrees (below, left). Since the mirror cell and mirror are linked together in this way, the mirror can not move in relation to the mirror cell or the roller skate wheels. So, unlike in many other systems, there is no friction whatsoever on the mirror when the telescope moves up and down!

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