OS42050SF-SFP

  Magnification :20x——4x
  Effective objective diameter (mm)  :50——29.6
  Exit pupil diameter  (mm) :2.5——12.5
  Eye relief  (mm):85——105.8
  Field of view Feet@100Y  :5.62——29.11
  Diopter adjustment  :-2.2——+2
  Center tube diameter  :30mm    
  Water proof  （Yes/No） :YES    
  Elevation travel  (MOA)  :±25
  Windage travel  (MOA)  :±25
  Click value :0.05MIL
  Parallax Compensation  :20Y ～～∞
  Ocular tube diameter  (mm)  :Φ43.5
  Coating :    Fully Multi-Coated
  Length  (mm) :336.3
  Weight (g)  :901
  FFP or SFP: SFP  

In the medium-to-long-range shooting equipment system, the 4-20X50 SF-SFP specification stands out as the preferred choice for hunting enthusiasts, shooting beginners, and pragmatic users due to its fixed and clear differentiation display and flexibility in adapting to various scenarios.
1. Core specification parameters
The parameter system of 4-20X50 SF-SFP is designed around the dual requirements of "practical observation + precise aiming", with each indicator serving differentiated use scenarios:
4-20X magnification range: The 4x low magnification provides an open field of view of over 12 meters/100 meters, suitable for rapid search at close range from 50 to 200 meters (such as hunting in the woods to spot prey); the 20x high magnification can zoom in on details of targets at 800-1200 meters, meeting the needs of precise shooting at medium and long distances. The 5x zoom ratio covers the entire process from "search and discovery" to "aim and strike", making it especially suitable for shooting scenarios where frequent magnification switching is not required.
50mm Objective Lens Diameter: The combination of a large objective lens and full multi-layer coating achieves a light transmittance of over 90%, ensuring bright and clear imaging of targets even in low-light environments such as dawn and dusk. Compared to smaller objective lens models, the 50mm aperture effectively mitigates the light attenuation issue at a high magnification of 20 times, balancing high-magnification observation and imaging quality.
SF (Side Focus) side focusing function: The adjustment range is typically from 10 yards to infinity, and the parallax error at different distances can be precisely eliminated through the side knob. Within the core usage range of 100-800 meters, the fine adjustment accuracy can reach 0.1 MOA, ensuring a high degree of overlap between the aiming point and the impact point, which is a key performance support for mid-range shooting.
SFP (Second Focal Plane): The reticle is etched on the focal plane of the eyepiece, and its size remains unchanged regardless of magnification. This design ensures that the reticle maintains a clear and easily identifiable size across the full magnification range of 4-20x, especially preventing visual fatigue caused by overly fine reticles during low-magnification searches. However, it should be noted that the reticle's distance measurement and ballistic compensation scales are only accurate and effective at the highest magnification (20x), and parameter conversion is required for use at lower magnifications.
II. Core Performance and Technical Advantages
(1) Optical performance: Balanced and adaptable for multi-scenario observation
The SFP specification focuses on "full magnification clear display" in optical design, taking into account both imaging quality and operational convenience:
Coating and Light Transmission Design: Utilizing Full Multi-Layer Coating (FMC) technology, it reduces glare interference under strong light conditions, ensuring clear target contours even in backlight environments. Equipped with a single-layer anti-reflective coating, it meets the needs of various applications.
Field of view and imaging balance: At a high magnification of 20x, the field of view is approximately 2.3 meters per 100 meters, while at a low magnification of 4x, the field of view can reach up to 12.5 meters per 100 meters, providing a broader view. This design offers significant advantages in medium-range hunting, allowing for quick locking on moving prey at low magnification while switching to high magnification for precise aiming at vital points.
Advantages of simplified structure: Since there is no need to design a differentiation mechanism that scales synchronously with the magnification, the SFP optical system has a simpler structure, higher optical transfer efficiency, and excellent imaging sharpness within a common range of 100-500 meters.
(II) Mechanical structure: Practical-oriented stable design
The SFP specification is centered around "reliability and durability + ease of operation" in terms of mechanical performance, catering to the usage habits of non-professional users:
Material and Strength of the Scope Body: Made of 6061 aviation-grade aluminum alloy through one-piece molding, and after undergoing hard anodizing treatment, it boasts an impact resistance rating of 800-1200G, accommodating the recoil forces of mainstream hunting ammunition such as .308 Win and .270 Win. It has undergone rigorous factory testing, ensuring its high-strength shockproof capabilities.
Simplification of the regulation system:
Turret design: Adopting either a "protective cover turret" or a "semi-exposed turret", with an adjustment accuracy of 1/4 MOA, omitting the zero-position locking function, simplifying the operation process, making it more suitable for beginner shooters.
Zoom mechanism: Utilizing a single spring and gear transmission design, the structure is more durable with a low failure rate. The zoom process from 4x to 20x is smooth without any noticeable stuttering, ensuring lower maintenance costs for daily use.
Environmental adaptability guarantee: With a waterproof rating of IPX7, it can be immersed in water up to 1 meter deep for 30 minutes. The anti-fog performance is achieved through nitrogen filling, ensuring no fogging occurs within a temperature range of -20℃ to 50℃, meeting the needs of most outdoor hunting and shooting training scenarios.
(III) Humanized design: Reducing the operational threshold
Differentiation and display optimization: The differentiation line is designed to be bold (typically with a line width of 0.2-0.3 MOA), making it clearly visible at a magnification of 4x, allowing for quick aiming without relying on illumination functions.
Exit pupil and grip design: With an exit pupil distance of 80-90mm, coupled with a fixed or two-position adjustable eye cup, even slight deviations in shooting posture can quickly provide a complete field of view. Coupled with a lightweight structure, it is less likely to cause fatigue when holding the gun for extended periods of time.
Accessibility adaptation: Most models are equipped with basic red/green lighting (3 levels of brightness), which can enhance visibility in low-light environments. The side focusing knob has clear markings, with each adjustment level corresponding to a specific distance, making it easy for novices to quickly grasp the essentials of operation.
III. Applicable Scenarios
(1) Core applicable scenarios
Medium-range hunting: such as hunting wild boar in the forest (100-300 meters), hunting deer in the grassland (200-500 meters). The low magnification and wide field of view facilitate the discovery of prey, while the 20x high magnification allows for precise aiming, and the SFP fixed differentiation reduces visual interference.
Shooting Training and Beginner Competitions: Ideal for novices to familiarize themselves with the operation logic of sights, with fixed differentiation lines to reduce the difficulty of ranging and ballistics calculations. The 4-20x magnification covers training needs ranging from rapid shooting at close range to precise shooting at medium range.
Outdoor observation and security: 20x high magnification allows for clear observation of distant targets, and the side focusing function ensures clear vision at different distances