A Simple Description of Optical sight:
**Main Classification of sight**
**Zoom Classification:Fixed-power and Variable-power
**Reticle Material Classification:** Reticle plate and Reticle wire
**Reticle Position Classification:** Front focal plane (FFP) and Second focal plane (SFP)
**Focusing Method:** Front focusing and Side focusing
**Fixed-Power Sight/Scopes:**
Pros:
- Fixed magnification with no zoom mechanism. These sight scopes are compact and offer excellent optical performance with minimal image distortion. They are highly shock-resistant and stable in operation.
Cons:
- The fixed magnification limits adaptability in dynamic situations such as combat or hunting. High magnification is not suitable for close-range shooting, while low magnification is insufficient for long-range observation.
**Variable-Power sight Scopes:**
The JAXY Variable-power
optical sight scopes emerged only in the past few decades. They are designed with an internal mechanism that allows the movement of the magnifying lens group to change the focal length ratio between the objective lens and the eyepiece. This is typically adjusted via a coaxial knob on the eyepiece tube.
Pros:
- Modern variable-power sight scopes have significantly improved optical performance, accuracy, and lifespan compared to earlier models. The zoom process requires extremely precise manufacturing and assembly to minimize errors. These sight scopes are versatile for both close-range observation and long-range precision aiming, offering greater flexibility.
Cons:
- The magnification should be within a reasonable range. Higher magnification narrows the field of view, making target acquisition more challenging. Additionally, the reduced field of view leads to decreased light transmission within the scope, resulting in less bright images. High magnification essentially zooms into a small portion of the low-magnification field of view, which can be dim and less clear. Therefore, it is not necessary to purchase sight scopes with excessively high magnification.
**Classification by Reticle Material:** Reticle plate and Reticle wire
**Reticle Wire:**
Pros:
- Reticle wire scopes are generally lighter and less prone to dust accumulation.
Cons:
- They cannot withstand strong impacts and have poor shock resistance.
**Reticle Plate:**
Pros:
- Reticle plate sight require high assembly skills and a clean environment to prevent dust and moisture, which can affect visibility. However, they are highly shock-resistant.
Cons:
- The reticle plate is located at the front of the zoom tube. When magnification is increased, any small specks of dust on the reticle plate will be greatly enlarged, affecting the appearance (high manufacturing process requirements). At low magnification, these specks may not be noticeable, but at high magnification, they can cover a significant area.
**Classification by Reticle Position:** Front focal plane (FFP) and Second focal plane (SFP)
**Second Focal Plane (SFP):**
The reticle is located after the zoom lens group and in front of the eyepiece. When the magnification is adjusted, the image changes, but the reticle does not scale with the magnification. This can lead to errors when using the reticle to measure the size or distance of objects. It generally has ranging capabilities only at the lowest magnification. When purchasing, it is important to check if the reticle is calibrated for a specific fixed magnification. If it is set for high magnification, it will only serve to magnify the image.
**Front Focal Plane (FFP):**
The reticle scales with the magnification, maintaining consistent subtension and size across all magnifications. The mil values remain constant at any magnification, ensuring no ranging errors. The reticle and ranging points are unaffected by magnification changes, making it suitable for ranging and aiming with auxiliary reticle lines at any magnification.
Cons:
- Since the reticle plate is at the front of the zoom tube, any specks of dust on it will be greatly enlarged at high magnification, affecting the appearance (high manufacturing process requirements). At low magnification, these specks may not be noticeable, but at high magnification, they can cover a significant area.
**Front Focusing:**
The focusing ring is located at the objective lens end. For example, AO scopes use front focusing, while AOE/AOIR models come with illuminated reticles. The advantage is that the focusing distance can be closer, but it may not be as comfortable or convenient as side focusing.
**Side Focusing:**
The focusing ring is placed on the side of the scope. Many people prefer this design for its aesthetics and convenience. Adjusting parallax is also easier with side focusing.
An optical sight scope consists of at least three lens groups: the objective lens group, the erector tube group, and the eyepiece group, with additional lens groups possible. The objective lens group collects light; the larger the objective lens, the brighter the image in the scope. The eyepiece group converts the light into parallel rays, allowing the eye to focus and achieve the maximum field of view. The erector tube group corrects the inverted and reversed image from the objective lens and adjusts the magnification.
The reticle can be located at the first focal plane (FFP) in front of the erector group or the second focal plane (SFP) behind it. The windage and elevation adjustment knobs, as well as the magnification ring, control the position of the erector tube group in terms of left-right, up-down, and forward-backward movements.
**Advantages of 30mm Tubes:**
The 30mm tube has a higher light transmission rate compared to the 25mm tube, resulting in a brighter field of view. Additionally, the larger tube diameter allows for a greater range of adjustment for precision tuning, making it easier to zero in at close range and enhancing close-range shooting performance. In simple terms, the larger tube provides more space for internal adjustments, and the most noticeable feature is the wider range of adjustment available. This makes it easier to zero in at close range.
Moreover, the light transmission of a 30mm tube is higher than that of a 25.4mm tube, resulting in a brighter field of view.
In sight scope design, many internal optical components are movable and can be manually adjusted via external dials to change the aiming point ("elevation" for the vertical axis and "windage" for the horizontal axis). The two central knobs on the scope are for precision adjustments. The one marked "Up" adjusts the vertical direction, also known as "elevation adjustment," while the one marked "R/L" adjusts the horizontal direction, known as "windage adjustment."
**Optical Coatings:**
Coatings on the lens surfaces reduce reflection and light loss, as well as eye fatigue. Coatings are typically made of magnesium fluoride. The more layers of coating, the better the optical performance. Multi-layer coatings are common, and both the eyepiece and objective lens usually have them, with most being multi-layer green coatings.
**Exit Pupil Diameter:**
The diameter of the visible range in front of the eyepiece. A larger exit pupil diameter results in a brighter image. It can be calculated by dividing the objective lens diameter by the magnification. For example, a rifle scope with a 3-9x40 configuration has an exit pupil diameter ranging from 4.44mm to 13.33mm.
**Eye Relief:**
Also known as the exit pupil distance, it is the distance between the eyepiece and the eye when the full field of view is visible.
The above summary is intended to provide a basic understanding of civilian optical sight scopes.
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