John Dobson fumes while shuffling between half a dozen homemade telescopes arrayed across a yard like cannons.

It's hot here in the Willamette Valley, and Dobson has been teaching pupils the intricacies of telescope building for three weeks, and he's losing patience. The heat is baking the old man's shirtless skin red, and his white ponytail glistens.

He roams among his students, some in their 30s and others who are seniors, as they polish reflecting mirrors by hand.

“Why would the light from the centre be brighter when it's out of focus!'' Dobson roars. Befuddled, the student freezes, stares at his telescope and suggests the centre of the mirror isn't hollowed out enough in the middle.

“So, the centre is too high!'' Dobson bellows. “Is that so complicated?'' He tells the pupil to hand polish the mirror more. Dobson knows his bellowing unnerves some students, but he'll turn 90 next month and he says he's too old to change.

And no one protests. They don't even bad-mouth him, so great is their reverence for the man.

A champion of inexpensive equipment, and a populariser of space, Dobson was instrumental in raising the status of amateur astronomy to near-professional level.

To his admirers, Dobson's a hero, and to his detractors he's a crackpot. And for those who have gathered in Monmouth — his stargazing disciples — it is an honour to sit at the feet of the master (never mind that the three-week class costs $120, plus about $350 for materials).

He does what he does, knowing his place in the annals of astronomy is set. Nearly 50 years ago, he was thrown out of a monastery for sneaking off at night to make cheap telescopes out of scrap.

Now he spends 10 months a year on the road, living with fans, sharing his well-honed telescope-making techniques and giving lectures on the nature of the universe. He accepts nearly every invitation to “star parties,” the semi-social, all-night gatherings of amateurs.

He jokes that he is famous for being too dumb to build an equatorial mount, the expensive and complicated telescope base used by most astronomers before his Dobsonian mount came along.

But he hopes his legacy goes beyond his telescope design. He wants to be known for advancing his theory for the creation of the cosmos, a model he calls “bang free'' because it runs counter to the widely accepted big-bang model. “I prefer to be known as a cosmologist because I'm not interested in just the stars,'' he says. “I'm interested in the whole ball of wax.''

On a Friday evening in a classroom at Western Oregon University in Monmouth, Dobson sits on a chemistry lab table, putting on a show for about 40 astronomy buffs who sit riveted as he explains his theory of the cosmos. But this is no dull science lecture. Dobson is animated, bellowing at times to get his points across. He swings his feet and tells jokes.

Someone asks if Dobson believes in God. ``Yes, but I don't have her number,'' Dobson quips. ``You seem to be a bit of a maverick,'' another man tells him. ``No, you can take out the `a bit' part,'' he says.

Dobson's ideas don't always get such an accepting reception. Physicians and cosmologists dismiss his theory, calling it misguided and unsubstantiated. But they credit Dobson's other contributions to astronomy.

``John Dobson is worth his weight in gold,'' Fred Watson, astronomer-in-charge of the Anglo-Australian Observatory at Coonabarabran in New South Wales says via e-mail. ``Because of his development of a cheap, easy-to-make type of amateur telescope, his name has become part of the everyday currency of telescope making.''

After his lecture, Dobson walks through the parking lot. It is after 9 p.m. and a dozen telescopes, mostly handmade Dobsonians, are pointed at the dark Oregon sky, including a few made by the students he berated the day before.

Dobson strolls past; he rarely looks through the eyepieces. He has seen all they have to show.