what is it? help please

[djhickory]

i got this from my grandpa as a gift years ago, he told me that it was used to take pics on a spy plane really high, was wondering if there is a name for this type of lens so i can look more up on it, and see if it has any value?
thanks very much

pics_ - MyPicx.com

 

[Dwig]

Its some form of catadioptric lens (aka "mirror lens")

Catadioptric system - Wikipedia, the free encyclopedia

It was probably a low production custom lens, possibly a one-off. Without some sort if ID plate or marking it would be a rather difficult task to track down the fabricator.

 

[KmH]

I concur. Catadioptric optics have a folded light path so the actual length of the lens is only about 1/2 the total focal length of the optical system.
a camera was placed in front of the small glass at the back of the lens, in the left hand photo.

The secondary mirror is quite a ways in front of the corrector plate (right hand photo).

An 800mm Bower mirror lens:

Bower 800mm f/8 Manual Focus Telephoto T-Mount Lens

They make telescopes too, using that optical system;

http://www.shopatron.com/products/category/1323.0.28926.44280.0.0.0