[dtuomi]

Originally Posted by old_tv_nut

Vidicon cameras, yes, but not this model. The rotating gradient neutral density wheel for exposure was a technique also used in vidicon film chains.

See the Tk-26 here:
http://www.oldradio.com/archives/har.../RCA-TV.htm#q2

edit: "TK-25" typo fixed to "TK-26"

I have to say, I never grow tired of that website.

David