Leupold Sequoia 20-60X80Mm Spotting Scope Kit 61135

The spotting scope's generous eye relief and twist-up eyecups ensure comfortable extended viewing, even with eyeglasses. The multi-coated lens system ensures maximum brightness, clarity, contrast, and color fidelity. Other features include a focus dial conveniently locate atop the scope for ease of adjustment and a built-in tripod adapter port. Armor coated and waterproof, it's covered by the Leupold Limited Lifetime Warranty.

Specifications:

• Actual magnification: 20x to 60x
• Linear field of view: 99.6 - 33.2 feet @ 1000 yards/30 - 10 meters @ 1000 meters
• Angular field of view: 1.9 - 0.09 degrees
• Objective aperture: 80mm
• Twilight factor: 40 - 69.3
• Exit pupil: 3.9 - 1.3mm
• Eye relief: 19.9 - 15mm
• Close focus distance: 30feet
• Weight: 62.8 ounces
• Length: 15.9 inches

What is Twilight Factor?
The factor that has the greatest impact on resolution or image detail, will be dependent upon the amount of light available during the time of observation. During daylight hours, when your eye pupil size will be only about 2 to 3mm, magnification will be the principal factor in image resolution. At night, with the eye pupil dilated to 6 to 8mm, aperture size is the controlling factor. In twilight conditions both of these factors control resolution effectiveness and the twilight factor is the term that compares binocular performance under these conditions.

The twilight factor is calculated by taking the square root of the product of the magnification and the aperture. The higher the twilight factor, the better the resolution of the binocular when observing under dim light conditions. For example, a 10 X 40 (twilight factor 20) would effectively resolve better under these conditions than a 7 X 35 (twilight factor 15.4) even though the 10 X 40 has a smaller exit pupil. Remember, however, that the twilight factor does not take into account the transmittance or quality of the optical system.