In this article we will explain the adjustable lens, which is the front focus. It is a very useful adjustment that allows you to optimise the focus at different distances.
Adjustable lens of a viewfinder
To begin with, it should be noted that there are 3 types of parallax adjustments: front (objective), side and rear. To learn more about parallax and how to mitigate it in your rifle scope, you can visit this article: What is the parallax of a rifle scope?
In some riflescopes, the image at very short distances can appear clear but with blurred reticles; with a parallax adjustment this problem can be solved perfectly. This happens because the image and the reticle are not in the same focal plane. This type of fine focus adjustment is generally reserved for high magnification riflescopes. It basically consists of an adjustment ring on the front (objective) lens or a side wheel that can be turned until the best focus for that distance is found.
There is an ergonomic difficulty in using front parallax adjustment scopes because you have to reach the front of the scope for adjustment while looking through the scope. This problem is accentuated in standing and kneeling positions. Some models of riflescopes have a resettable calibration ring. Other riflescopes, on the other hand, have a zeroing feature where most of the front assemblies do not rotate.
On most front focusing scopes the front lens housing rotates as a whole. This can present some difficulty in rotating smoothly and is a consequence of there being a knock-on effect on distance estimation, because the scopes have not been designed with their use for distance estimation in mind. Therefore it is a simpler structure that does not have too many optical elements, however the possibility of errors is very low.
There are different tricks to read distances more easily: for example, rings around the target or a prism to see the numbers from the shooting position. Left-handed shooters may find this type of rifle scope more comfortable than a rifle scope with side parallax.
Examples of adjustable target riflescopes
Examples of riflescopes with adjustable lens may include:
- Leapers UTG 6-24x50 rifle scope
- Bushnell Banner 6-24x40 viewfinder
If you want you can see more adjustable objective scopes at Carbin.
