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By Stephen F Tonkin

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Because of the nature of the Teflon, the holes in the strips tend to close up, rather than loosen and tighten around the threads, locking the screws in position. Since the Teflon strips are secured at each end by the four pairs of screws, the strips do not require anchoring to the wall of the tube in order to hold the screws tightly. After installation into the holder tube, the eight screws adjust the stalk's position. The screws, while held firmly by the expanding Teflon, easily adjust with an Allen key.

1 The original focuser and star diagonal. The prism is visible Collimation My collimating tool is a plastic 35 mm film can in which I have drilled two 2 mm holes, one each in the dead centre of the base and the lid. I have found that the easiest way to collimate a refractor is to do so in two stages. First, remove the objective and tape a cross-"hair" of string across the "big end" of the tube. The film can goes into the focuser and the focuser end of the telescope is waggled until the cross is visible through the holes in the can.

The Concept The conventional refractor is undoubtedly a fine instrument which produces high-contrast images. Among portable instruments, a refractor is therefore certainly the kind of telescope that offers most performance per inch of aperture - however, by no means per foot of tube length! But is there anyway out of this trade-off? Once I already had a nicely portable 15 cm (6 in) f/5 Newtonian, I started wanting an even more portable telescope, but one that was optically better. I considered the few options, but neither was I happy with a handy SC (Schmidt-Cassegrain) telescope, because of its compromised resolution and contrast caused by the central obstruction, nor did any fast focal ratio, apochromatic refractor appeal to me - especially when I looked at the prices!

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