The Dobsonian telescope T300

Here the telescope that from now on I use. It is intended for an exclusively visual use for the moment. It was carried out in six months of work out of covered plywood external of three layers of varnish marine. The side bearings are dismountable

The collimation of T300 is carried out very simply in two stages. The first consists of an alignment of optics using a laser . This alignment is carried out with the three screws of collimation of the spider, the primary mirror having been aligned beforehand at the time of the first light of the telescope . The completion of collimation itself is carried out on Polaris using a short focal eyepiece.This last adjustment is carried out via two nuts allowing the adjustment of the slope of the 9 points flotation system primary cell. Two points of adjustment are enough, the third being made up by a pivot. The finalization of collimation is thus carried out by the top with the result that for at least one of the adjustments I can see directly in the eyepiece the effect of the turn of key given what return the handling of an extreme simplicity! However, the key is provided with a fastening to the hand using a adequate strap to avoid the possible fall of the key on the primary mirror... The Telrad researcher from now on is equipped with an electric resistance in oder to avoid dew. Used eyepieces for this scope: Televue Nagler 26mm T 5 2" and Nagler 12mm T4 2" and 1.25" - 82° of field -. - The Pentax XW 7mm and 3,5mm / 1.25"- 70° of field - Filter OIII 2" Lumicon.

Nota: the first three photos of this page were taken by Fabrice Vergé-Borderolle

Details of the secondary cage. The spider is tended and fixed at the rings using aluminium squares recovered on amount of window. The secondary mirror is not fixed with glue, it is attatched at the carry-secondary using four adjustable claws in height for before and the back and in slope for the side claws. The focuser board is carried out using an aluminium sandwich of 4mm in order to give him rigidity necessary to the use of the heaviest eyepieces. A rigid baffle paints in nut husk color associated with mate varnish in plywood 5mm was installed in the opposite side of the focuser. Additional black plastic flexible bafflages made up of sorter are envisaged if necessary using fixing scratch.

Sight of underbody of the primary box posed on its rocker. One sees the electric fan fixed at the center of the mirror cell.It accelerates the temperature setting of the mirror which is lower than one hour. This fan models extra dish and silencer is supplied by a small battery 12V/2.1 Ah located itself inside the primary mirror box. This battery is also capable to supplie the anti-dew of the Telrad. We can adapt also counterweight in this box. The mirror cell is a model with three triangles of floating out of 4 mm thickness stainless steel. On each one of these triangles three Teflon points (with slow frozen Araldite after preliminary abrasion) are glued constituting the supports of mirror.

Some steps of the construction of the secondary cage: Sight of left: Standard structure honeycombs of one of the rings of the secondary cage. Each ring consists of triple sandwich three thicknesses of assembled plywood with waterproof white wood glue. The greatest thickness is of 10mm, it is that which is dug to receive the structures. In the center: sandpapering of the two rings sets for on the one hand giving them a perfectly circular form and on the other hand so that they are rigorously identical. Sight of right-hand side: spider in the course of construction. Structure aluminium and screw in stainless.