The lenses have an internal and an external bayonet arrangement. This allows filters
or close-up lenses to be installed without stacking the lens hood which bayonets on the external
lugs. At left we have the plastic lens cover. At the top is the lens hood, below that a +1
close-up lens set (one for the viewfinder and one for the taking lens). In the front, a yellow
and a red filter. These are all "Bay I" fittings (which also fit some Rollei TLRs).