It sounds silly to ask such question or stumble in such problem, indeed! But I was willing to make some small telescopes for young friends of mine, to encourage them to delve in the skies. So, I bought: 1. Double concave, spherical glass lens, with a focal length of approx. -75mm and diameter of 38mm. 2. Double convex, spherical glass lens, with a focal length of approx. 1000mm. I believed that by a tube of about a meter length, I should have an excellent refracting telescope! But unfortunately after collecting the lenses and the tube, the telescope did not work! Sth is hugely wrong in my estimations! Would anyone hint me where might the mistake be? Your illustrations are much appreciated.