Lawrie
Joined: 25 Sep 2008
Posts: 13
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 Posted: Wed Oct 08, 2008 6:06 pm Post subject: Finders |
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Finders
A problem common to most amateur telescopes is the inadequacy of the finder provided. Of many telescopes used over the years, rarely has any finder been very useful. They have invariably been awkwardly placed making them difficult and uncomfortable to use and their quality can leave much to be desired. Their only virtue seems to be that they look good in the sales blurbs.
On an early 10" alt/az reflector it was replaced with a "rifle sight". This was a 3/4" wide strip of 1/8th thick aluminium about 12" long. Three inches at each end was bent up at right angles. One end had a V notch filed in it whilst the other end was filed to a point. The points had a dabs of luminous paint and the whole thing was mounted on the old finder mount. It merely required that a star be placed between the V points and "balanced" on the rear point for it to be centred on the main scope. This was far easier to use and more convenient than trying to squint up the old finder.
Nowadays, with "health n'safety" regulations, this device would probably be considered too dangerous to use in the dark. In any case luminous paint, which is radio-active, is almost impossible to buy now.
Red Dot finders are another possibility. They, like the rifle sight, are used with both eyes open which makes them easy to use, although there is still a some awkwardness when trying to find the position where you can see the red dot! They use batteries which usually run out just when you haven't a spare handy and it is too easy to leave the finder on after a session which can aggravate the condition.
Green Lasers. Special mounts can be bought for them and there is now a specific finder device which uses one. Otherwise one has to fiddle about with the push-down switch and they are not very effective if the air is clean and dry. They rely on a certain amount of moisture in the atmosphere to show the beam. In any case their use is a little controversial as cases of irresponsible use have resulted in prosecutions! |
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