Why does it 'have' to auto-focus?
I bought the AFS35 & 50 for my daughter, and they are great lenses, and she loved them, b-u-t? For what they are worth.... I have an old M42-fit Pentacon 29mm prime, and a Ziess 50, among the many for my old film camera, and an adapter is a lot cheaper....for the price of even the 'cheap' AFS50 I could probably procure an adapter and most of my M42 lenses... true, the D3200's metering doesn't work with them, and you have to shoot full-manual exposure and focus, but what the heck; IF you are playing in this realm you probably would anyway. However....
For all so many rave about the bokah achieved by certain lenses, its not, repeat NOT a facet endowed by the lens. The primary 'feature' that endows a photo with Bokah, is the subject.... Bokah is the 'quality' of out-of-focus high-lights in the scene..... so you need that in the scene before you start or you wont get none. Then, that detail has to be rendered out of focus... so, you need the camera to subject distance to be a lot shorter than the hyper-focal distance, and the back-ground to subject distance large enough that it falls distinctly out-side the Depth-Of-Field.
THIS sort of 'basics' is far more important than the lens, and if you cant get bokah effects with what you got.... another lens probably wont help much.
Longer Lenses will 'help'. Longer focal lengths have further close focus distances, and further hyper-focal distances, so it tends to be easier to get a more favorable ratio of Camera-Subject : Subject-Background distance ratio to shorten the Depth-Of-Field and get background to oof, and maybe provide some Bokah. Likewise faster aperture lenses, will shorten the DoF and do likewise.... B-u-t.... The bokah is either in that background or not, and achievable through the camera-subject to camera-back-ground ratio, or not,
Back to those AFS prime's... on a crop-sensor camera, you are working against the mechanics; the small sensor is a convenience to camera makers;
for starters they are cheaper to make; next begging shorter lens lengths for the same effective framing, they inherently have a greater DoF which gives them a greater tolerance on the complex and expensive Auto-Focus mechanism; hence the fashion for very fast f1.8 or f1.4 aperture primes, where those fast apertures shorten the DoF and allow the same 'sort' of effects people used to get with 35mm or 120 roll film cameras, and much more conservative apertures.... and in the case of 120 roll film I mean REALLY conservative apertures!
Fastest aperture on my 120 'folder' is f6.3, but, it's 'normal-angle' lens is a 105mm focal length, giving the same approximate framing of a 50mm on FF/35mmFilm, or 35mm on APS-C widgetal. Consequently the hyper-focal distance is that much further away from the camera, whilst the near focus is only brought usefully close to the camera, only by being a folder, the lens mounted on bellows like a macro-set up. But, exploiting that, you can get some wonderful 'selective' focus effects and Bokah backgrounds from it, without resorting to incredibly low f-numbers.
This is actually what lead to the manufacturers arms race to provide low-f-no 'Fast-Fifty' lenses with 35mm SLR's in their hey-day; the exact same phenomenon of the smaller format shrinking lens lengths and shortening near and hyper-focal ranges, lead to the fast-fifty being the placator to let 35mm SLR folk get the same 'sort' of more arty dissociation focus effects medium and large format cameras had achieved incidentally through shear scale.... and its the same trend being promoted in smaller format Digital... somewhat perversely, IMO.... the 'effect' is still not in the gear, its in the subject and the set-up, NOT the lens.
Understand whats achieving that Bokah background, and you can get it; don't, and it'll be shear chance.
B-u-t, like I said, the small format APS-C sensor size is working against you, not for you, and neither longer telephoto nor faster aperture lenses will help you.
Worth mentioning with APS-C, is that when you DO achieve disasociative focus, the effect can look distorted, and the subject appear photo-shopped into the scene rather than a part of it, because in using shorter lenses and wider apertures, the 'focus fade' from front to back in to out of focus can become very sharp.... which puts even more on you as photographer to make the effect appear 'natural' in the way you USE the gear, rather than the gear you CHOOSE.
Oh-Kay! 18-55 kit
ISTR you have one of these, came as standard with the D3200. Its f3.5 at the wide-side, f5.6 at the long; Covers zoom range from 18mm wide, through 35mm normal, to 55mm mild tele, equiv aprox 80mm on full frame, the usual 'portrait' recomend.
So! What you got! Is what I recommend, for starters!
The kit lens covers the range you are looking at as far as faster primes, what it lacks is a little clarity and a bit of aperture; but it is 'cheap'! And that lack of aperture is no big deal.
For portraiture, the usual niggle is focusing on the eyes, and getting ears and noses in focus too, but getting the back-ground to oof.....
Hence question at top, WHY is AF so critical?
Here NOT relying on the red-dots and going manual-focus, you have the 'control' to put the critical focus exactly where you want it, and exploit the Depth-of-Field zone around that, to put the near and far focus limits exactly where YOU want them to be in your scene, NOT what the red-dots arbitrarily decide.
Now, your more moderate aperture can actually be an asset not a drawback, giving you more DoF to keep noses and ears in acceptable focus, whilst you DONT necessarily focus exactly on the iris, and have wide aperture shallow DoF making it so shallow you just cant get both ears and nose both in acceptable focus wherever you set critical focus distance.
A manual-Focus '50' would then tend to demand this bit of technique from you, and the results you would get from one would most likely be because of that technique NOT the lens..
Hence, suggestion you DONT need a new lens; just use what you already have differently and learn to get what you want from it, setting the scene, and exploiuting the focus range and DoF zone.
And If you 'must' buy something.... then for portraiture, back-drops, lighting, props... would possibly be higher up the list of priorities, and if that is still not enough.... then well, debate over AF and MF lenses is probably some-what mute, and the whole start point of a sub-small format camera comes into the question... but that's for you to ponder.
The Nikon 50, whether its the older pin drive 'G' that wont auto-focus (but will auto-exposure) on the D3200, vs the 'D' that will, or a legacy Manual-Focus film camera lens on adapter,. is more irrelevant in that that it ever was.
Back to what I say and what I do; I 'do' the manual focus legacy lens thing, 'cos having the lenses already its as cheap as breathing. What I also 'do' is buy AFS 50 'D' for daughter... 'cos she don't have legacy lenses for free, and do expect camera to meter and focus with whatever she sticks on the front, with the warning "GO Manual FOCUS, before you go Manual Exposure!", and she doesn't have 18-55, and was effecting craft in academic photo study at O, A and now degree level, not nievely expecting gear to get her what she hoped for.
So, I think its a small switch of thinking that's really required, not so much a switch of kit. You probably already have the kit that will get you what you hope for, and a lot more, IF you evolve the craft to go with it. Looking to retail solutions, you will never get all you could, and just a big shopping list.
Your call....
