Teleconverter

Optec Inc. is based in the US state of Michigan, and their motto is "Helping astronomers measure the stars since 1979". By this, they mean the electro-optical devices for spectroscopy, photometry and focusing which they manufacture and distribute.

From focusing aids to controllable filter wheels for astrophotography to highly sensitive photometers to measure the brightness of stars (magnitude), Optec operates in a very specialised niche area of astronomy.