Astronomy Hacks

Upgrade Your Optical Finder

Match your optical finder to your type of telescope and your observing habits.

An optical finder is a low-power, wide-field refractor telescope with a crosshair eyepiece. The finder has a much wider field of view than the main telescope—typically 4° to 8° versus perhaps 1°—so it is much easier to acquire an object in the finder than with the main scope. If the finder is properly aligned with the main telescope, centering an object in the finder crosshairs also centers the object in the field of view of the main telescope.

Most inexpensive and midrange telescopes come with some sort of optical finder. The type, size, and quality of the finder varies with the size and price of the scope.

• Cheap small scopes include a cheap, tiny finder, usually 5 power with a 24mm single-element plastic objective (5X24). These so-called finders are worse than useless and should be replaced immediately with something better.

• Mid-size and mid-price scopes usually provide a 6X30 achromatic finder with coated glass lenses. A 6X30 finder may be usable until you can replace it with something better, but it provides insufficient magnification and light gathering. A 6X30 finder shows stars not much below 8th magnitude, which is not deep enough for serious use. Unless you observe Luna and the planets only, make it a high priority to replace the 6X30 finder with a suitable 50mm finder.

• Larger and more expensive scopes may include a 7, 8, or 9X50 achromatic finder with multicoated glass ...