Roger Van Haelewyn
Each classic refractor or reflector is equipped with a small finderscope. This device helps to find celestial objects, and to put their image on the optical axis of the main instrument.
Normally the finder is a small refractor with a large field of vue and a crosswire in the eyepiece; the modern finder uses a laserbeam.
For the amateur sunobserver it is risky for his eyes to use a finderscope or any other device pointing at the sun. There exists no practical system and normally the observer uses the method of the "shortest shadow", moving the refractor or telescope until he observes the shortest and "roundest" shadow of the instrument on the ground. Some people are very handy but also a lot of them are fumbling and moaning, especially when using higher magnifications and smaller fields. When the instrument is alt-azimuth mounted the "problem" is obviously more ennoying.
Why not build a "sunpointer" ?
Our sun is undoubtedly a strong source of light, throwing shadows of each object.
To build a sunpointer we need an "object" and what we use as such, only depends on our phantasy. In my sunpointer I use a nice piece of plastic recuperated out of an old dishwashing machine. It is a piece of a square grid and has a beautiful geometrical form throwing precise shadows.
The shadow of the grid falls on a small projection screen, not a nontransparent metallic plate but a semitransparent piece of glass, glued to an aluminum window. With a permanent marker a shadowsection of the object has been drawn on the semitransparent glass. The whole device is fixed on a metallic base which can be positioned relative to the optical axis of the refractor or telescope with the aid of three adjusting screws and one blocking screw.
The adjustment of the whole system permits to put the sun's image on the optical axis when the shadow of the "object" falls exactly on the drawing.
The nice thing is the semitransparent glass screen : you can see the shadow of the "object" through it and at the same time move the instrument to find the correct position, without leaving the eyepiece !
Very simple, efficient and fast to use !
Photo 1 : shows the device mounted on a TeleVue 101 refractor next to a Starbeam finder with laserbeam
Photo 2 : details of the three adjusting screws and the blocking screw
Photo 3 : the projection screen with the semitransparent glass, the drawing of the shadowsection and the shadow of the object.
Photo 4 : the "object", my phantasy
Roger VAN HAELEWYN
Mol, Summer 2001
