Subject: Quetions about optics of periscope

If the colour of the internal part of the periscope tube is black in colour, 
how does it affect the image? Why? If it is coated with a silvery surface, will 
we be able to see the image? How about a white surface on the internal part of 
the tube? 

How does the length of the tube of  a periscope affect the image? Why? 

I have gone through a number of books but is not able to get an 
answer. I will appreciate very much if you can help me. Thanks a million! Have 
a good day.

Re: Quetions about optics of periscope