A Note on Lenses and Cameras
In the app, lenses belong to just one camera, so if you have a lens which you use with multiple cameras you'll need to add it for each of the cameras.
The reason for this design is that although users of common camera systems (e.g. Nikon F-mount) can use the same lens on multiple bodies, many times that is not the case. For example, Mamiya and Hasselblad are different systems.
To avoid incompatible lenses showing up for a selected camera, we implemented the app so that each lens belongs to just one camera. (We also decided not to try to implement a "many to many" design due to the increased complexity of the UI design that would entail for users.)
To Add a Lens
Go the Lenses page on iPhone:
or tap the Lens button on iPad:
Next, tap the '+' button at the top right to add a new lens:
In the next screen, you can choose the lens type and focal length, and optionally specify a custom name for the lens (a default will be used if you choose not to):
Tap 'Save' to save the new lens. It will then be available in the lens list (for the currently selected camera):