Lisäokulaarit

Lisäokulaarit, often referred to as Barlow lenses, are optical devices that screw into the focuser of a telescope or microscope and are then inserted into the eyepiece holder. Their primary function is to increase the magnification of the optical instrument. They achieve this by optically extending the focal length of the objective lens or mirror. A common Barlow lens has a magnification factor of 2x, meaning it doubles the effective focal length of the telescope and therefore doubles the magnification achieved with any given eyepiece. Other common magnifications include 1.5x, 3x, and 5x.

The Barlow lens typically consists of a negative lens element housed in a barrel. When light from the telescope's objective passes through the Barlow, it diverges before reaching the eyepiece. The eyepiece then gathers this diverging light and brings it to a focus, effectively creating a longer path for the light and thus higher magnification. This magnification increase is calculated by dividing the effective focal length of the telescope with the Barlow by the effective focal length of the telescope without the Barlow.

Using lisäokulaarit offers several advantages. They allow a telescope owner to achieve a wider range of magnifications without needing to purchase a large collection of eyepieces. For example, with a 2x Barlow, one can effectively double the magnification of each of their existing eyepieces. This can be particularly beneficial for planetary observation, where higher magnifications are often desired. However, it's important to note that while magnification increases, the true field of view decreases, and image quality can degrade if the Barlow lens is of poor optical quality or if the telescope is pushed to its maximum useful magnification.