Yeh can relate to what you commented. Its either they get freaked out and you take no photos or they get friendly until your hands are full and you can't take their photos too.
I am not familiar with a 50mm prime (non macro) but say with a minimum focusing distance of 0.45m and magnification ratio of 1:5 or 1:6 against the size of a cat's eye whether it will be possible to capture much close up details, presumably of course the cat stay stills and all other odds negated. But with a telezoom (say 200mm, 55-200mm, 70-300mm) even with lower magnification ratio zooming in can capture much details. But for these lens unless they are also 1:1 macro lenses or with close up attachment capturing much smaller subjects (e.g smaller insects) in details may not be that appropriate.