A cloth bag full of souvenirs brought back by astronaut Neil Armstrong has come to light, more than 40 years after the Apollo 11 moon landing.

The trove includes a 16mm movie camera from inside the lunar module that filmed its descent to the moon and Armstrong's first steps on the lunar surface in 1969.

That camera "took one of the most significant sets of images in the 20th century", said Allan Needell, a curator in space history at the National Air and Space Museum.

Mr Needell, who called the bag's discovery "extraordinarily exciting", said the museum had been told about it in June 2013 by Armstrong's widow, who had found it while cleaning out a cupboard. Armstrong died in 2012.

The long process of documenting the find concluded only recently, and that is when the museum decided to go public.

The museum is already displaying the camera in a temporary exhibit.

Mr Needell said the images taken by the camera were far more detailed and clear than the grainy ones shown on TV at the time of the landing. The film cartridges had been removed during the mission so the device itself was no longer needed.

The camera would have stayed on the lunar module, which crashed on the moon's surface after delivering the astronauts back to the orbiter, Mr Needell said, but Armstrong, Buzz Aldrin and Michael Collins "decided to take some souvenirs home with them".

It had long been common knowledge that astronauts sometimes took pieces of unneeded equipment as souvenirs, Mr Needell added. Congress recently passed a law approving the practice.

The cloth bag also included other small pieces of equipment, including a waist tether Armstrong used to suspend his feet during a rest period while the module was on the moon.

The Armstrong family loaned the material to the museum and has pledged to donate it, Mr Needell said.