Ocular lens

Ocular Lens

Ocular Lens also known as the Eyepiece, is the lens or collection of lenses which is closest to your eye.

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The Ocular Lens is the lens or collection of lenses which is closest to your eye. The lens assembly typically consists of a plano-concave lens, and a combination of bi-convex lenses, spacers, and double concave/double convex lenses.  The lens is housed in the ocular bell also known as the eyepiece.

It is the Ocular Lens that is typically adjusted to alter the focus of the reticle for the viewer’s eye.

Ocular lens
Ocular lens

It is vitally important that you focus the scope (reticle) to your eye before you do anything else. Skip doing this and everything else will be out of kilter!

Ocular lens
Ocular lens

The journey of the image to your eye

The Objective Lens

As we discussed in our article on the Objective Lens. Light travels from its source, reflects off the object we are looking at and is viewed by our eye.

These light waves are considered in physics to be travelling in straight lines.

The objective lens collects these light waves and bends them (refraction) to one point, this is called the focal plane.

Due to the nature of this process, the image is inverted (upside down). See the following diagram:

The diagrams in this article are not technically accurate either in scale, accuracy or mathematically.  They are just simple representations of the process.

Objective lens to first focal plane
Objective lens to first focal plane

The Erector Lenses

The image needs to be inverted once more (rectified) so it appears upright at our eye.  This is achieved by the Erector or Reversing Lenses.

Erecting Lenses
Erecting Lenses

The Ocular Lens

The image is then carried to the Exit Pupil by the Ocular Lens.

Objective Lens to Exit Pupil
Objective Lens to Exit Pupil

In fixed magnification scopes the Erecting lenses are attached and immovable in the tube.  On variable magnification scopes the Erecting lenses are typically attached to framework which can move forward and back.

This changes the distance of the focal plane to the Ocular lens, thereby altering the magnification.

More on this in an upcoming article on scope magnification and zoom. We will also cover focus in the same manner.

FAQ (Frequently Asked Questions)

The ocular lens of a rifle scope is the lens closest to your eye, commonly known as the eyepiece. This is the opposite end to the objective lens which is closest to the target.

The ocular lens is the lens closest to your eye. The objective lens is closest to the target or object. It is the task of the objective lens to collect the light reflected off the target and deliver that image to the ocular lens.

The ocular lens focuses the image gathered by the objective lens at the other end of the rifle scope, presenting the image you see when you look into the eyepiece. 

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