1. How is the exit pupil calculated?

The exit pupil is calculated by dividing the diameter of the lens by the magnification, for 8 x 56, the result is:

(56:8) = 7mm

An exit pupil that is larger than 7 mm cannot be fully used by the human eye.

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2. What is an objective?

An objective is the lens at the end of the scope facing the object being observed.

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3. What is an eyepiece?

An eyepiece is the lens at the end of the scope facing the observer.

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4. What is focusing?

Focusing is the adjustment of an optical device to give a sharp image at varying distances.

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5. What does internal focusing mean?

If the focusing of the optical device can be achieved without having to move an exterior lens or part of the housing, then this is called internal focusing.

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6. What is a monocular?

A monocular is a device that is designed for use with one eye only, such as a telescope or a telescopic sight..

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7. What does 'coating' mean?

A 'coating' here means the improvement of the optical properties by means of thin films (at the μ-metre level). The type of coating is important for the light transmission or for filtering out unwanted frequencies of light which can negatively influence colour fidelity, or for anti-reflection treatment of optical surfaces.

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8. What is the 'field of view'?

The area that can be seen when looking through a scope is called the field of view.

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9. What does 'variable magnification' mean?

There are adjustable and fixed magnifications with binoculars, spotting scopes and telescopic sights. For example, a '3-12x56' is an instrument that allows a magnification range from 3X up to 12X. The last value ('56') refers to the diameter of the lens. Thus, you can decide which magnification to select for a particular distance..

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10. What is a 'twilight number'?

The twilight number provides information about the low light performance (image resolution properties) of telescopic sights. Simply put, it is the calculated performance of the binoculars or telescopic sight in low light conditions.

The low light performance is calculated as follows: square root of magnification multiplied by the lens diameter; for example a telescopic sight with the specifications 8 x 56 has a Twilight Number of:

√(8x56) = √448 = 21.2

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11. What does 'reticle' mean?

A reticle is the aiming aid (crosshairs, dot, etc.), that is built into the instrument; it can be of various different designs. Common forms are the 'cross-hairs' (of various thicknesses) or a (light) point.

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12. What is a 'centred reticle'?

This is a reticle that remains in the centre of field of view even after using the reticle adjuster. Older telescopic sights do not have generally have this feature.

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13. In which optical plane should the reticle lie?

The plane in which the reticle should lie is primarily dependent on its use, the type of reticle and the preferences of the shooter. There are two locations in which the rays of light intersect within a telescopic sight. The first intersection is located behind the objective lens, where the reticle is mounted in the part of the adjustable inner tube facing the objective lens. The second intersection lies to the rear, facing the eyepiece part of the inner tube. The effective difference is that the lenses responsible for the magnification are mounted between these two mounting options. A location in front of the magnifying lens causes the reticle to be magnified together with the target image. A location behind the magnifying lens means only the target image will be magnified. The ratio of the reticle dimensions to the target image dimensions then changes with the magnification.

A reticle in the first image plane (the objective image plane; the European type of construction) does have the advantage that the distances always remain the same, but the disadvantage is that these are almost imperceptible at low magnifications and that at large magnifications they can obscure a small target. So this system is well suited for telescopic sights with smaller zoom ranges..

A reticle in the second image plane (the eyepiece image plane; the American type of construction) only has well defined distances at some magnifications, but always appears the same size to the eye. These are therefore easily visible at any magnification and do not obscure the target. So this system is well suited for telescopic sights with larger zoom ranges.

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14. Can the reticle also be adjusted?

Yes, with modern instruments there is both a windage and elevation adjuster. With older lenses there is often only a horizontal adjuster. Here, horizontal adjustment is provided for by means of the lateral movement of a mounting block.

New telescopic sights (with a few exceptions) are adjusted via click-knobs. For European made telescopic sights, the reticle adjustment is usually 1cm per click.

Non-European products usually have an adjustment of ¼ M.O.A. (M.O.A. = minute of angle), i.e. ¼ of an angular minute, which corresponds to about 7 mm at 100 m.

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15. For which applications are different magnifications used?

For drive hunts = a low magnification of 1X to 4X

Stalking/from a hide= 1.5X to 12X

For hunting in twilight/at night = a high magnification of 3X to 12X

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16. What is a mounting?

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