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What are some differences between cheap and expensive telescopes?
Wiki User
∙ 10y ago
There are hundreds of progressive lenses (also known as multi-focal or vari-focal lenses) available and they vary in price massively. The price mainly depends on the type of "design" of the progressive lens surface. Older style "conventional" progressives lenses are made using semi finished blanks. A semi finished blank is a lens which is already half made. The progressive (graduated) lens surface has already been ground onto one side of the lens. This is the part where all of the channels/corridors and reading additions are ground. An example of one of these lenses is a Hoya Summit Pro or an Essilor Varilux Comfort lens. With a conventional progressive lens, when your glasses are ordered, the lens laboratory will grind your prescription onto the other side of a semi finished blank. The wearer may find that they will be aware of distortions when they rotate their eyes to look away from the center of the lenses. Because of these problems, new lenses have been developed to reduce these optical errors (perceived by the wearer as distortions). "Free form" lenses have been designed to compensate for the errors. This means that the lens manufacturer takes into account the eyes rotation and tries to correct the errors that usually occur at every pin point on the lens surface. This technology is usually ground onto one side of the lens only but the lab will still use a semi finished blank to make the lenses. An example of one of these lenses is a Hoya iD LifeStyle (formerly called an "FD") lens. There are also lenses available which are completely customised to suit the wearer and they will be made completely from scratch without using a semi finished blank. They will also compensate for the optical errors at every point on the lens but this will be done on both sides of the lenses. This type of lens is the best option for any progressive lens wearer but it is also the most expensive. An example of one of these lenses is a Hoya iD Classic (formerly called an "iD") lens. Another thing that can effect the price is the lens material and any coatings or extra options such as transitions.
Wiki User
∙ 14y ago
Wiki User
∙ 10y agoThe differences between telescopes lies entirely with the optics. The eyepieces in cheap equipment usually are poorly made and just not as clear. Another important factor is the telescopes stability, one that is flimsy is almost useless.
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