Astronomical telescopes are becoming ever more popular with consumers as their prices have come down. Quality astronomical telescopes are now widely available at fairly reasonable costs. This has created a large number of inexperienced users of astronomical telescopes. It is common for such telescopes to come equipped with a variety of accessories, including, for example, various ocular lenses, erecting lenses, Barlow lenses, prismatic diagonals, etc. Many other accessory types are also available, including a penta mirror diagonal and special zoom lens which are available from the assignee of the present invention.
A problem arises when an inexperienced user attempts to use multiple accessories in series which are, in fact, optically incompatible. For example, compound lens systems such as are found in an erector lens, a zoom lens or a Barlow lens significantly reduce the amount of light reaching a user. Prismatic diagonals are also compound lens systems which considerably reduce the total light transmitted there through. The light penalty associated with combining some of such compound lenses in series, e.g. associating a prismatic diagonal with a zoom lens, is too great for practical viewing. Thus, the zoom lens cannot be used in conjunction with a Barlow lens and a Barlow lens should not be used with an erector lens. Finally, due to practical limitations, the zoom lens cannot be used with an astronomical telescope without also using the penta mirror diagonal.
It is clear, then, that a need exists for a system and method which prevents an inexperienced user from attempting to use optically incompatible telescope accessories in series with one another. Such a system and method should be inexpensive and easy to implement, yet also easy to understand.