Lens Templates

[vcmaes]

I recently read an article with tips for improving your photography skills. They make mention of A. Adams taking photo walks w/o taking his camera, just a yellow filter, a note pad, and a "cardboard cut out approximating" the field of view.
I like the idea and would like to give it a try, so I'm wondering if there are any PDF files, or an equivalent file format, with templates that approximate different lens field of views (i.e. 35mm or 50mm)?

What have you all heard about this, and/or the availability of such templates?

Thanks,
Vince