What do magnification and objective diameter mean?
The designation 4–20 × 50 gives two specifications: magnification can be adjusted from four times to twenty times. The front lens, called the objective, has a stated diameter of 50 mm. Higher magnification makes an object appear larger. It does not, by itself, tell you how sharp, contrast-rich or colour-accurate the image is.
The designation 4–20 × 50 gives two specifications: magnification can be adjusted from four times to twenty times. The front lens, called the objective, has a stated diameter of 50 mm. Higher magnification makes an object appear larger. It does not, by itself, tell you how sharp, contrast-rich or colour-accurate the image is.
The zoom ratio is the highest magnification divided by the lowest. For 4–20, the ratio is five. A scope with a completely different magnification range can have the same zoom ratio. A high zoom ratio alone therefore does not mean higher quality.
Do not confuse objective diameter with main tube diameter. The main tube is the housing section between the wider ends. A thicker main tube does not automatically produce a brighter image. A useful comparison also considers field of view, eye relief, weight and size, along with verifiable information about image quality and mechanical performance.