Understanding optics...

The Objective Lens

The objective lens is the big lens at the front of a telescope or the big lenses at the front of binoculars.

The diameter of the objective lens, measured in mm, is just as important at the magnification as its size determines how much light can be gathered to form an image. The diameter of the objective lenses will control how much light the binocular or telescope can collect. In bright conditions the lens size will not be so important, but larger lenses will be able to maintain the brightness of the image even in poor lighting or at night. A small diameter objective lens gathers less light than a large diameter lens.

In general terms, the more light that is gathered through the objective lens, the brighter and sharper the image will be at your eye.

Usually the greater the number of times that the magnification can be divided into the objective lens diameter, the brighter the image will be. Therefore a 30x80 objective lens will produce a brighter and sharper image than an 30x60, even though both enlarge the image an identical thirty times.

- What do the numbers on my scope mean?

- What is magnification?

- What is the field of view

- What is an objective lens?

- What is eye relief?

- What is the exit pupil?

- Twilight Factor

- Relative Brightness