Question

A person can see clearly objects lying between 15cm and 100cm from the eye.what will be the range of his vision if he wears close fitting spectacles having a power of 0.8 D?

Answer 1

For each diopter the image size is increased by 25% so the images you see with .8 diopter lenses are 20% bigger.  Usually focal length is decreased when magnified but since glasses work in stereo I suppose that your focal length along with range of vision would remain roughly the same.