I hate to be a party pooper, but I once had the opportunity to use a Petri 7S and I was not favorably impressed. My wife owned the camera when we got married in 1973 (it was a gift from a friend who had served in Vietnam and had purchased the Petri from an Air Force exchange).
We took the Petri 7S as a backup camera when we went to South America in September, 1973 to conduct field research in an Amazonian Indian community (we stayed until March, 1975). My other cameras were a Canon FT-QL SLR and a late 1950s Beauty Super II rangefinder (made by Taiyodo Koki of Japan).
The Canon and Beauty cameras performed magnificently in the jungle. The Petri 7S tended to underexpose most of its shots. I think its meter (encircling the lens) was collecting more light than the lens itself, and giving erroneous readings. As a consequence, I have never liked cameras whose meters encircle their lenses.
The Petri lens itself was capable of making sharp images, but its color rendition was excessively warm ... much warmer than the lenses of the Canon and Beauty. Color slides made with the Petri appear almost reddish.
Finally, the film transport mechanism on the Petri 7S started skipping, leading to uneven frame spacing and overlapping exposures.
For me, the Petri 7S was one of the least robust and most disappointing cameras I ever worked with. It seemed flimsy compared to the Canon FT-QL (no surprise there), but it also seemed flimsy compared to my much older Beauty Super II rangefinder.
