What is eye relief?

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	What is eye relief?

Answer The proper way to look through your scope is by placing your eye just behind the eyepiece to take advantage of the eyepiece’s eye relief.

Eye relief measures the spacing from the last surface of the eye lens of an eyepiece to the plane behind the eyepiece where all the light rays of the exit pupil are visible. (The eye lens is the lens of the eyepiece closest to your eye when the eyepiece is inserted correctly into the focusing drawtube.) Your eye should be positioned here to see the full field of view of the eyepiece.

Eye relief should be at least 15mm for the best comfort, maybe more if you wear eyeglasses.

You’ll lose field of view if you place your eye farther away and may even move your eye out of the beam of light from the eyepiece. Getting too close will prevent you from blinking and also cause a black ring to appear around the field of view.

Longer-focal-length eyepieces generally have longer eye relief. Using a Barlow lens with them to increase magnification will allow more comfortable high-power viewing because the Barlow will keep the eye relief constant.

Eyepieces with long eye relief will need eyecups (rubber or plastic circular rims) to shield your view from extraneous glare.

Article Details

Article ID:

2377

Created On:

May 13 2010 04:53 PM