This is part I of a series of what glass you will need. Each part will discuss a certain lens type and its applications
Standard prime lenses had been the base of each SLR equipment since the earliest days. Virtually all SLR were sold in a kit with a 50mm f/1.8 and many of us never used anything else. In range-finder world the slightly wider 35mm was the standard.
It is said that a 50mm would give you a field of view similar to our vision (I stick with the FX convention for FOV<->focal-length, for DX divide by 1.5). This is somewhat true. Our field of vision is much wider, but the zone where we see sharp much narrower. I think the main reason for the “nifty-fitfties” is that they are the widest lenses with a still rather simple design: The focal length is larger than the flange distance.
So do you need it and what do you expect from it.
First of all, this primes are rather fast glass f/1.8 or even f/1.2 with some exotic lenses going down to f/0.95. With the exception of 85mm you don’t find many lenses faster than f/2.8 and virtually none fast than f/2. In film days speed was much more important as today - a D90 @ISO 1600 is on the level of ISO400 film of that epoch (higher rated films where actually pushed ISO 400 films). Today it is hence more about “bokeh” and “creative photography with limited DOF”.
Still, shooting in impossible light is now possible. If this is your interest ( I got a 35/1.8 for shooting at an anniversary at home without bothering people by a flash). Get the fastest lens you can afford or are willing to pay for. Prefer speed over everything else. bokeh is rarely an issue in low light photography and you couldn’t care less about sharpness in the edges.
Yes, sharpness in the edges wide open is completely irrelevant! Remember that you have a very small DOF field, it is almost out of question that another object of interest will be in the corner of the frame and still in focus.
Standard primes are as well good lenses for landscape. This is where the FOV argument from above makes sense, the impression of distance you get from the photo is rather close to how we see it. Still it is gospel that landscapes are shot with wide angles. I like to take exception here: If you what to go for a certain effect wide angles and tele lenses are the tool of choice, but for the typical panaroma shot you waste pixels on endless regions of sky. Consider shooting a panorama and stich it, the resulting image will have a much higher resolution and you don’t even need a tripod with modern software, this image had been made with Microsoft ICE (free and easy to to use):
You will like shoot at f/5.6-f/8, perhaps sometimes an individual you want to isolate at f/2 or faster. Virtually any prime can do that and sharpness is almost always good enough. Prefer lenses with fast AF unless you are a master of manual focus (really difficult with DSLR viewfinders). For portrait you have to be careful with the background with lenses that show a nervous bohkeh (50mm 1.8D, all 35mm) or have a strong bokeh-fringing (all 1.4 <=50mm, 35/1.8). When stopping down lenses with rounded aperture blades create a smoother image, but an old 6-bladed aperture can create beautiful effects, especially with flares
Obviously, you need to shoot rather wide open. As long as you shoot fully open you might have to take of highlights that show fringes, stopping down to f/2.8 usually fixes it, but as well reduces them and creates “stars” This can be desired, prefer straight and fewer aperture blades for this effect (the stars will have as many points as there are aperture blades if there number is even, uneven numbers give twice as many and less defined points). Forget about manual focus in the night, get the 50mm AF-S 1.8 (1.4G is you relly need 2/3 extra light), the other lenses don’t do to well with highlights unless stopped down.
This is something rather special and prepare for spending money. Most fast lenses exhibit coma and this will ruin your stars off-center. Very few lenses are corrected for that, the 58mm NOCT and the 85mm 1.4G … well the price tag is rather high. Stopped down coma becomes less relevant, but that requires longer exposures or higher ISO. You get the picture, this is rather specialized stuff and without top-notch equipment you results will have limited quality.
Is there one lens? Not if you cover everything. My over-all recommendation are the 50mm AF-S 1.8G or the 35mm AF-S 1.8G. If you are going to shoot more outside go with the fifty, otherwise the 35 will give you more room