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What does ER stand for?

ER stands for Eye Relief (optics)

This definition appears very frequently and is found in the following Acronym Finder categories:

  • Science, medicine, engineering, etc.

See other definitions of ER

Other Resources:
We have 64 other meanings of ER in our Acronym Attic

Samples in periodicals archive:

First, depending on your eyesight and the individual scope, focus can have a material effect on eye relief.
The comb height of the stock, the eye relief allowed by the stock length and access to the charging handle all must be considered when choosing the mount.
1 mm of eye relief at 7x, a field view of 288 feet at 1,000 yards and a close focus distance of 26 feet, along with a 7-15 power zoom range, multicoated precision lanses and high index prisms.