Answer  Tasco — One of the largest distributors of optics for sports, recreations and professional activities, has been called by some, "Trashco"!

Tasco's product line lists binoculars, night vision devices, telescopes, microscopes and magnifiers to riflescopes, pistol scopes, electronic aiming devices, spotting scopes and sport/sun glasses. The companies products are widely sold in department stores and the brand has widespread name recognition. However, Tasco (and many other astronomical telescope brands) are often advertised by magnifying power—the quoted magnifications are often excessive for the telescope aperture, quality of optics and telescope mount. Any telescope can usually be made to produce almost "any magnification" — but will you see anything?

For an example, see the Tasco product information page on Galaxee Astronomical Telescopes. Here is advertised a 675 power, 60mm refractor telescope. Such telescopes will not produce useful images if used at powers above approximately 120x! Tasco provides oculars to make the telescope produce a magnifying power of 675x so the advertisement is not wrong. However, Tasco does not tell you that you "won't see anything" at that power!

Note: The magnifying power of a telescope is simply found by:

Magnification = Effective Focal Length of Telescope / Focal Length of Eyepiece = F / Fe

Example: If F = 1000mm and Fe = 25mm, then mag. = 1000mm/25mm = 40x.

(Barlow lenses are sometimes used in conjuction with eyepieces to multiply the magnification. Thus, if a 2x Barlow is also used, the result is not 40x but 2x40 or 80x.)

So, by inserting into the telescope eyepieces of different focal lengths, the magnification is changed.

But, both light gathering power and resolving power are more important than magnifying power

• Light gathering power is most important   — Without light, there is nothing to see!
• Resolving power is second in importance — Without resolution, the image will lack detail!

  (Aperture . . . the diameter of the telescope's primary lens or mirror . . . determines both of the above quantities.)

• Magnifying power is the least important of these three properties.
  
  

Note: Here is a general rule to estimate the "maximum useful magnification":

50 x Aperture (inches)  or  2 x Aperture (millimeters)

So, in above example, 2 x 60mm = 120x.

(Often poor optics and shaky mounts may limit maximum useful magnifications to half of this.)

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