How Far Can You See Through A Telescope ?

Since the brightness of distant celestial objects, usually depends on the distance from them, a telescope with a large aperture (lens diameter) will show you not only weaker but also more distant objects. For example, a 60-mm refractor you able to observe the Andromeda galaxy, located away from us more than 2 million light years away. In the 200-mm telescope you can see the spiral arms of the weaker Whirlpool Galaxy, distant from us as much as 35 million light years! When using the telescope for ground-based observations the maximum distance to the observed objects is limited to the state of Earth's atmosphere. High humidity and rising from the earth heat flow blur images of distant objects. Increasing the telescope varies depending on the eyepiece. It is the ratio of lens focal length F (Lens) to the focal length eyepiece F (Eyepiece): Increase = F (Lens) / F (eyepiece) Search facility is always advisable to start with the eyepiece, which gives the smallest increase, and then switch to a more powerful eyepieces. Barlow lens doubles the two-time any increase in the eyepiece with which it is used. For example, the focal length of your telescope is 900 mm. When viewed from a 20-mm eyepiece increase of 45 times. If the front of the eyepiece lens set 2x Barlow the increase would rise to 90 times. The same increase could be achieved by using 10-mm eyepiece without the Barlow lens.