To see objects through a telescope it must be pointed to exactly the rightspot. The Telrad is sight for pointing telescopes to that ″rightspot″.
Through a Telrad you see the sky the way the star charts show it. Not asmall unside-down and magnified portion of it, but the ″realsky″ with three lighted target rings set against it. The large ringis 4 degrees across. It outlines the area covered by a finderscope. Thesmall ring is 1/2 degree across and outlines the area seen in thetelescope.