Periscope photos from U-boats

[vimza]

I'm looking for information on how photos was taken from the periscope by U-boats in WWII. I seen pictures on google but no details on how it was done. Was it a built in feature of the periscope?

[Rhodes]

I think that they just lean the camera lens on the periscope eyepiece.
Do not know if they had some special apparatus for the lens camera fit the eyepiece.