same lens for both photos, and both photos (Hatinh langur and Delacour's langur) are unmodified which will give an idea of the difference in distance (i.e. the Delacour's langur photos are not cropped).
The cliffs where the Hatinh langurs were is on the other side of a river - I suck at estimating distance but the river was probably as wide as a main street in a city, plus both I and the cliffs were set back from our respective river-banks by about the same distances again. (Actually, the cliffs were further back from the river than I was on my side). So the sort of distance where I could watch them easily with my binoculars, but they only look small in the photos.
For the Delacour's langurs - at the point where this photo was taken - the boat I was in was maybe ten metres out from the outcrop and the monkeys would have been up about ten or fifteen metres on the cliff. Several animals actually came right down to the bushes at the water's edge but none of those photos came out because the monkeys were mostly hidden behind foliage.
