Of course there is a bigger change in focus from 20m to infinity than 100m to infinity.
It is unlikely a young person could afford a £2,000 binocular.
It is primarily the type of eyepiece that determines whether the field is curved or not.
Distorted or not.
Fatigue is more likely in older people or those with some eye problems.
Also those with larger prescription dioptres, astigmatism, prism problems.
Also the focus of the eyes changes during the day, and day to day.
Young people may not notice this.
I would think that any difference between roof prism and Porroprism binoculars may be perception or psychological.
Also many binoculars are slightly out of alignment, and as viewing gets longer, more fatigue will set in.
It will also depend on lighting conditions and pupil size.
Lower magnification binoculars, like 5x25 or 6x30 will need less focus changes.
6x18 or 6x20 also.
Also, again, curved field eyepieces change the situation.
B.
It is unlikely a young person could afford a £2,000 binocular.
It is primarily the type of eyepiece that determines whether the field is curved or not.
Distorted or not.
Fatigue is more likely in older people or those with some eye problems.
Also those with larger prescription dioptres, astigmatism, prism problems.
Also the focus of the eyes changes during the day, and day to day.
Young people may not notice this.
I would think that any difference between roof prism and Porroprism binoculars may be perception or psychological.
Also many binoculars are slightly out of alignment, and as viewing gets longer, more fatigue will set in.
It will also depend on lighting conditions and pupil size.
Lower magnification binoculars, like 5x25 or 6x30 will need less focus changes.
6x18 or 6x20 also.
Also, again, curved field eyepieces change the situation.
B.