Related Clues:

• Fish-eye, e.g.
• It helps keep you focused
• Copier part
• You can see right through them
• Film, in Variety-speak
• Magnifying glass
• Something to see through
• Periscope part
• Eye piece
• It's see-through
• It helps keep one focused
• Lorgnette part
• Contact, for one
• Something found in specs?
• It helps you focus