Manufacturer quote twilight factor

Is there a DIN standard ?

Somehow I cannot see what's quoted is what I am seeing

Am I the only one observing this ?

"Twilight factor" is just a formula; it does not take the quality of glass or optical coatings into account.

A cheap Chinese 8x56mm would have the same twilight factor (and exit pupil) as a Zeiss 8x56mm.

George

If all things were equal in the optical qualities of an instrument, the the one with the higher "twilight factor" would provide better resolution of an object in low light. However, as GeorgeS says, "twighlight factor" is only a formula and may not be a fully accurate gauge of low light resolution.

What the twighlight factor is based on is the assumption (largely true) that when illuminated to the same degree, a larger object is more easily seen than a smaller one. Therefore, the greater an instrument's magnification (all things being eqaual), the greater its low light resolution. As you can see, there are some obvious practical limitations to this theory. But it does make for a great advertising gimmick.