Originally posted by CedrusMacro Do tell more Eric... any links or information would be appreciated.
Now you've made it sound a lot cooler than it probably is
Here's a set I found just now for a slightly more modern camera...
ZYKKOR CAMERA LENS SET TELEPHOTO & WIDE ANGLE for Minolta Hi-Matic AF2M Unused - DECADESGONEB4
They live on today in the "ultra-fisheye" conversion lenses for phones and digital cameras. Same basic idea.
Lots of companies made them (I have a Petri set for my Petri and a Yashica wide angle for my TLR) from probably the 1950s.
Normally, they came in a small leather case, one wide-angle and one telephoto. They just screw into the front of the lens like a big filter.
There is often a conversion scheme printed on the lens to help with focus, and there will usually be some hint for exposure compensation.
On a camera with a TTL meter (or, like the 7s, next to the regular lens and through the converter lens) the camera handles that.
Since you're just adding something on top of the lens and not optimizing the optics, they tend to not be great.
Mine flare like mad and lose definition, particularly at the edges, where things can get a bit smeary.
If you are really lucky, you'll find a kit with a viewfinder that goes in the hot shoe. If I remember right, Soligor made a nice one...
-Eric