They're called bus fans. Some spend a great deal of money on expensive cameras and long-range lenses to capture the shots of the fleet's most interesting buses.
Dennis Tsoi Sheung-lam and Ho Man-chak are bus fans, too, but as teenagers, they've had to learn to pursue their hobby on a budget.
Dennis, 15, a Form Three student at SKH Li Fook Hing Secondary School and Man-chak, 16, a Form Four student at HKFEW Wong Cho Bau Secondary School, use only basic digital cameras to take snapshots of buses. The cameras cost about HK$1,000.
"It is true that we can't get pictures of buses moving fast," Dennis said. "But we've learned to be smart. We find safe positions on the streets where we can capture buses that are stationary or that have just started moving."
Hundreds of buses have been taken off the road in recent years because they're too old, forcing bus companies to bring in new models. Many bus fans can be seen carrying the latest cameras as they race to get pictures of both the disappearing buses and their replacements.
You might spot the fans at terminals, intersections, roundabouts or even perched on footbridges, taking pictures of the bus you're travelling on.
The boys love being bus fans, even if they have to use cheaper cameras. "We're not ashamed that our equipment is not as good as that of other established bus fans who can afford to buy better cameras," Man-chak said. "We only want good photos, and we can get what we want with our cameras."
Dennis and Man-chak started the hobby two years ago. They met while following a brand new Citybus model on its first day in the summer of 2011.
Since then, the duo have paired up to photograph buses at the airport.
Bus fans usually pick an area of interest before they start taking photos. Dennis aims to collect pictures of all 66 buses in the Cityflyer fleet, which travel to and from Hong Kong International Airport. Man-chak focuses on Long Win buses, which serve the airport, Tung Chung and Hong Kong Disneyland.
"As we are students, we can only do this time-consuming hobby on the weekends," said Man-chak. "Instead of standing on the street for hours, we collect info about the order of the buses on the routes we would like to photograph.
"I usually take photos at Tung Chung bus terminal, which is quite close to my home," he said. "Some drivers are friendly, and they tell us when a particular bus will arrive. I can then go home and do something else and come back hours later when the bus I want is really coming."
Dennis, however, lives in Siu Sai Wan, quite far from the airport. Instead of taking the A12 bus to the airport for HK$45, this bus fan takes the train.
"I first take bus to Central and take the MTR to Tung Chung," Dennis said. "Then, I take another bus to the airport. It costs only HK$19.2 one way. It is much cheaper, and I found that my unique route was even faster than the one the A12 bus takes."
Dennis is saving up to buy a better camera, so he even walks to school.
"I am saving every bit to get new equipment for my hobby," Dennis said. "However, this is not an urgent call. Right now my target is to compete against time."
Dennis hopes to get photos of every Cityflyer bus before the fleet is replaced in about a year.
"So far," he said, "I have half of them, and I still have more than 30 to go."