I have a D5200. I'm planning on to buy a prime lens and I'm also interested in macro photography. I had chosen to buy the Nikkor 35mm prime lens. But, I came across the 40mm Nikkor Macro lens. Now I wonder if I can use the Nikkor 40mm for both macros as well as portraits, or I should also buy the 35mm Nikkor for portraits?
Does taking portraits using the 35mm (f/1.8) give a significant advantage over the nikkor 40mm macro (f/2.8)?
There is a lot going on here with many questions you have asked.
The main question I believe you are asking is, can you use a macro lens for portrait photography? We already have at least two questions on this site that address that:
The second question you are asking is how close in angle of view or perspective is a 35mm vs a 40mm lens. We also have many answers to this question already on this site, but I think heading off to the Nikon Lens Simulator is the best way to understand this:
Finally, the two lenses you noted have very different apertures. f/2.8 is quite a wide aperture, but f/1.8 is significantly wider. f/1.8 will let in almost 4x as much light, letting you handhold the lens in lower light, use faster shutter speeds, or simply get a shot that would otherwise be too underexposed. That is a very significant difference.
I would advise if you want a macro lens, to get something around a 100mm macro lens. If you want a portrait lens, the great news is that 100mm also is a fantastic focal length for portraits. 40mm and even 35mm(on an APS-C sensor) is certainly on the wide angle side of what most people prefer for portrait photography. A 50mm or a 85mm might be the sweet spot on APS-C although longer is often used too.
I don't think you want either of these lenses for your stated purposes of macro and portrait . They'll work, but not necessarily be most ideal. (As dpollitt also notes, see Is a macro lens suitable for distant subjects - wildlife, sports, portraiture?.)
First, normal and wider macro lenses are used for document reproduction, but not usually for the kind of insect or nature or whatever macro photography people usually get interested in. For those, you usually want a longer lens, because that gives you a good working distance — more on that here. The working distance for true 1:1 macro with the 40mm is just 3-4cm from the front of the lens! So, you probably want something like a 90mm or 100mm macro. (Or 60mm — Nikon makes a decently-regarded and relatively low cost 60mm f/2.8.)
Also echoing dpollitt, on APS-C, anything in that same range makes a nice focal length for portraits. Of course, any focal length, can take portraits, but traditionally this is the sweet area for easily flattering results. (More on that at Which focal-length lens is usually used for portrait photography, and why?). 35mm and 40mm on APS-C give a focal length that's just below that traditional portrait range — pretty decent for full-body shots or maybe a little closer, but too wide for the classic portrait lens.
So, I think if I were you, I'd start there — somewhere with a longer focal length. Then, either of the 35mm or 40mm would be a nice complement than that. (You can never have too many lenses, right?)
As for which if these to get for general shooting... They're both fine value-priced options. I've only used the 35mm, but as I understand the consensus, the 40mm is a bit sharper and had a nicer rendering of out of focus areas (bokeh) — while the 35mm saves you $75 and gets you a little over a stop more light. The sharpness shouldn't really be a deciding factor for general use (both are fine and sharpness is often overrated), and with today's great high-ISO sensors I wouldn't sweat the speed difference either. (Sure, faster is better, but so is getting more of the scene in focus, and even f/2.8 gives too-shallow depth of field for typical indoor scenes if you have more than a single subject dominating the composition.)
I shoot with a 40mm on my Pentax APS-C DSLR all the time, and find it a very useful and versatile focal length. However, indoors, I do sometimes wish for just a few degrees more field of view, as 35mm would give you. Again, this comes down to six of one and half a dozen of the other. You might try renting both lenses for a bit and deciding which fits you best after a week or two of shooting with each.
I started with the 35mm 1.8.
I bought the 40mm as an inexpensive toe in the water of macro. My interests are the natural world, not documents or staged items. I'm pretty happy with it.
I discovered, pretty much by accident, that it shoots a nice portrait when there's plenty of light. The bokeh is attractive.
I also have the 35mm, which I use for the wider aperture and just general composition.
