Twilight factor and twilight performance

Calculation of twilight factor and statement on twilight performance for binoculars

The visual acuity of the human eye decreases with age. TwilightFor night glasses, which are ideal for sitting game and as sow glasses, the light intensity is the most important feature. " More info to around a third of daytime visual acuity. The eye's sensitivity only increases for the blue spectral range.

In order to be able to recognise details over long distances even in twilight, binoculars with a high MagnificationThe magnification of a binocular model is perhaps the most misunderstood feature. High magnification can be useful! " More info and corresponding Twilight performanceIn order to be able to recognise details over long distances even in twilight, binoculars with high magnification and corresponding twilight performance (e.g. 10x56 or 8x56) are recommended. " More info (e.g. 10×56 or 8×56).

The twilight number and thus the Calculated luminous intensity and results from Enlargement and Lens diameterThe larger the lens diameter, the more light can be absorbed by the lens of the optical system. Glass purity plays a major role. " More info of binoculars:

8×56 binoculars have a twilight factor of 21.2, which means that you can still see an object at a distance of 212 metres. The twilight factor gives a purely  calculated value for the image brightnessbut which is also characterised by the optical construction, different types of glass and the quality of the RemunerationIf light hits a glass-air surface (e.g. with a roof prism), the reflection causes a loss of light. " More info is influenced.

Important: One High twilight number stands not simultaneously for high or good twilight performance!

A 30×75 spotting scope, for example, with the impressive twilight index of 47.4 is not suitable for observations in twilight with an exit pupil (see below) of only 2.5mm.