Introduced in 1972, and using the same 42mm screw mount as the Pentax Spotmatic F (with additional coupling inside the body to allow for open aperture metering with lenses so equipped), the Pentax ES was the world's first 35mm SLR with fully electronic shutter speed control. There is an Automatic setting on the speed dial to select this feature.
I picked up this black ES body at the camera show last weekend for a very low price, since there were issues, and it was sold mainly as a collectible.
I also picked up these two Hanimex branded long lenses, one f:2.8 / 135mm, the other f:4.5 with a 90 - 230mm zoom. They were very very cheap at the camera show.

This morning I packed them up in a little kit, loaded the body with a roll of Kodak 200 print film, and headed to the St. Louis Zoo to test out the work I did on camera and lenses.
In the field, the electronic shutter control system was intermittent and unreliable, and failed to be usable. However, the camera does have manual speeds from 1/60 second to 1/1000, so I reverted to them, using guestimates for exposure values, with occasional consultations with my hand held Gossen meter.
The camera body did feel good in the hand, and mechanical functions were very smooth.

Please click on thumbnails to see enlarged.
All images are Copyright 2012 E.J.Kowalski.