The Jaipur Observatory from atop one of the 12 Rasivalayas
Sawaii Jai Singh was however, aiming for a clearer picture of the entire sky and the systems that governed it, for which his Yantras were eminently suitable.Anisha Shekhar Mukherji, Jantar mantar: Maharajah Sawaii Jai Singh’s Observatory in Delhi.
On the topic of why Jai Singh chose not to use telescopes in his observatories
Jai Singh built 5 observatories across northern India between 1721 and 1730. the decision to build multiple observatories at large distances from one another was in part a quest for accuracy; the ability to compare readings from different coordinates. But the observatories may also have played a role in strengthing Jai Singh’s political position in regions where he had gained authority. It is also noteworthy that the sites Jai Singh chose have historical, political, or religious significance:
Delhi was the seat of the Mughal Empire
Ujjain was the former capital of the Malwa province and is located on the prime meridian established by the ancient Hindu canons of astronomy.
Varanasi was an ancient center of learning, and reputedly the oldest continuously inhabited city in the world.
Mathura was the legendary city of Krishna
The first to be built was the observatory at Delhi in 1724 and the last to be completed was the observatory at Jaipur. ca. 1738
Of the five observatories, all but the observatory at Mathura still exist and are open to the public.
Jai Singh built 5 observatories in west-central India. All but the observatory at Mathura are in existence today