Leaf shutters are what were generally used in Rangefinder cameras - when being closed as a default setting is acceptable - unlike with an SLR when the shutter blades tend to make viewing very very very difficult if closed. And, if you did, then it would have a 'film door' behind the leaf shutter so you could remove the lens without exposing the film.

If you have an SLR camera with such a lens it will be a Kowa made no later than 1958 or an earlier German camera such as a Contaflex or Bessamatic. Where still used these are now invariably in medium of large format cameras, 'which you have not got'. In many cases where this is done the lens is not removable (in the usual meaning of the word). In a small number of designs a leaf shutter is used - mounted either in the lens - or behind the lens but in front of the SLR mirror so it must be open to focus and use the viewfinder. Long ago there were exceptions - I mention them here for education and 'fun', with no real expectation that you'll actually be using a Kowa, Contaflex or Bessamatic :-). In any camera that you are liable to be using, the shutter - which optically separates the film from the light - is in the camera body, and is closed except when a photo is being taken, so when you remove the lens the shutter will still protect the film.

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