this is a model for making a refracting telescope with a smart phone. The project was done during a weekend at the Nasa Apps Challenge 2014 in Montreal.
The design is calculated for the available lens that we got at an optometrist shop nearby. The spectacle is a 70mm diameter single vision F=3 CR39 with AR coating. Also, we supposed that the minimum focal point of the iPhone is 4cm in front of the telephone. This gives us a distance of something around 38-40 cm telescope length.