Comparison BRESSER Pirsch Gen II 20-60x80/45 WP vs Bushnell Trophy Xtreme 20-60x65

The field of view of the telescope at a distance of 1 km to the objects under consideration, the so-called "linear field of view". In fact, this is the width (diameter) of the space that falls into the field of view when observed from a distance of 1 km.

This parameter is widely used in the characteristics of telescopes along with the angular field of view (see below): the linear field of view data is more visual and closer to practice, it allows you to evaluate the capabilities of a telescope without resorting to special calculations.

For models of variable magnification (the majority of them), the linear field of view is indicated in the form of two numbers — for the minimum and for the maximum magnification.

The smallest distance to the object under consideration at which the telescope is able to fully focus on it — that is, the minimum distance at which the image in the eyepiece will remain clear.

Spotting scopes were originally designed for viewing distant objects, so focus problems can occur if the distance is too small. Thus, manufacturers indicate this parameter in the characteristics. However, even in the most powerful and "long-range" models, the minimum focus distance is about 25 m — at this distance, the naked eye is often enough. Therefore, you should pay attention to this parameter only in cases where the ability to work normally close is of fundamental importance — for example, if the pipe is used at a shooting range, where the distance to the targets can be different, including pretty small.

The diameter of the objective is the front lens of the telescope. The term "aperture" is also used for this characteristic.

The lens diameter is one of the most important characteristics of an optical system: the amount of light entering the lens and, accordingly, the image quality (especially in low light) directly depend on the aperture. From the point of view of optical characteristics, we can definitely say that the larger the lens, the better, especially at high magnification (for more details, see “Exit Pupil Diameter”). On the other hand, large lenses significantly affect the size, weight, and most importantly, the cost of telescopes. Therefore, manufacturers usually choose the lens size taking into account the magnification, price category and the specifics of the use of a telescope — especially since at low magnifications and good lighting, even a relatively small aperture may well provide a high-quality image. For more information about these patterns, see "Exit Pupil Diameter". In addition, it is worth noting that the features of the "picture" are affected not only by the mathematical characteristics of the optics, but also by the overall quality of its components.

Exit pupil diameter of a spyglass.

The exit pupil is the projection of the image "seen" by the tube that appears just behind the eyepiece. A person sees an image in a telescope precisely due to the fact that the exit pupil is projected onto the eye.

The exit pupil diameter corresponds to the size of the lens divided by the magnification (see above for both). For example, for a pipe with an aperture of 50 mm, operating at a magnification of 25x, this size will be 50/25 = 2 mm. At the same time, it is believed that in order to ensure the most bright and comfortable image, the exit pupil should be no smaller than the pupil of the observer's eye — and this is 2-3 mm in the light and up to 8 mm (in the elderly — up to 5-6 mm) at dusk. This is the reason why for comfortable work at high magnifications and/or in low light conditions, a telescope must have a fairly large lens. However, most of these optical devices are designed for daytime use, and for this, an exit pupil of 1.33 mm in size is sufficient.

For most modern telescopes, the exit pupil diameter is indicated by two numbers — for the minimum and for the maximum magnification.

Removal of the exit pupil of a telescope.

About the exit pupil itself, see above. Here we note that the offset is such a distance from the eyepiece lens to the observer's eye, at which the size of the visible image from the lens corresponds to the visible size of the eyepiece lens. In other words, the observed "image" in this case occupies the entire space of the eyepiece, without vignetting (darkening at the edges) and without "spreading" beyond the edges of the eyepiece. In this case, the overall image quality will be the best.

When looking down the pipe with the naked eye, the observer usually has no problem getting into the offset distance, and this parameter can be ignored. Problems can arise if the user wears glasses and the diopter adjustment (see above) is not sufficient to comfortably view without glasses. In such cases, it is desirable to use models with eye relief of at least 15 mm: although such a distance will not provide the highest image quality when viewed with glasses, it will allow using the device without any special difficulties. However, in modern telescopes, this parameter can reach 18 mm or even more.

Also note that eye relief may decrease somewhat with increasing magnification; in such cases, two numbers are indicated in the characteristics, corresponding to the removal at the minimum and at the maximum magnification.

The location of the eyepiece relative to the body (more precisely, relative to the optical axis) of the tube.

— Direct. In this case, the eyepiece is directed parallel to the optical axis of the tube — in other words, it "looks" in the same direction as the lens. In this case, the eyepiece can be directly on the optical axis or above it. The direct arrangement is convenient especially in those cases when the tube is used without a tripod and is held in the hands. It is well suited for observations from a shelter (for example, during hunting or wildlife research) — the observer does not need to rise above the body of the tube to look into the eyepiece. Also, this option is easier for novice users who have not previously dealt with optical instruments — it is more convenient to point the pipe at the target. In addition, when the eyepiece is located on the same axis as the lens, prisms can be dispensed with, which simplifies the design (although this arrangement in itself does not mean the absence of prisms).

— Under 45°. An eyepiece bent upwards by 45° relative to the optical axis of the tube. In many situations, this arrangement is more convenient for the observer. For example, it allows you to comfortably use a relatively low tripod (whereas a tube with a straight eyepiece must be placed at eye level, that is, either look for a high tripod or squat to the level of the eyepiece). In add...ition, for similar reasons, curved eyepieces are more convenient when observing objects above the horizon and celestial bodies. The disadvantage of this design is the unequivocal need to use Porro prisms (see "Prism type"), which can affect the cost. In addition, for a person without experience, aiming a curved pipe at the desired object can, out of habit, be quite a difficult task.

The presence of a tripod in the scope of delivery of the telescope.

This configuration is convenient primarily because it eliminates the need to purchase a tripod separately — and this can be quite troublesome due to the fact that the telescope can use a proprietary mount that is not suitable for standard tripods and requires at least the use of an adapter. Also note that a tripod can be useful not only for a massive telescope, which is difficult to hold in your hands, but also for a compact one that allows manual use — even a relatively light optical device is not easy to hold on weight for a long time.