Originally Posted by Stevopedia
I don't know what makes the Electro-Spotmatics so special.
That site will answer most of your questions.
The Electro-Spotmatic is really just an early ES, but a rare variant where it spells out Electro-Spotmatic rather than just ES on the body. The Electro Spotmatic is one of the more "uncommon" Pentaxs, and technically it was the forerunner (some say production prototype) of the Spotmatic ES. It was produced in small numbers.
The very early ES's, (and this includes the Electro-Spotmatics) were prone to circuit board failures. Consequently, It is hard to find and Electro-Spotmatic that works in Auto mode. This was fixed relatively quickly and most of the ES's have the revised design and still work.
Look at the page here:
Die Cast Pro - Asahi Pentax Electro-Spotmatic Index
Compare:
Die Cast Pro - Honeywell Pentax ES Index
woof!