vininnj2u wrote:
I am getting a 50mm lens to use with my Canon 80D. My other lenses are 18-135mm stm, 100-400mmLseries lens. Where can I expect to use the 50mm lens?
Most people would have a planned use or reason for making an additional lens purchase, so I guess that's what you mean by "putting the cart before the horse", huh?
On an 80D with its APS-C size sensor, a 50mm will behave as a nice, short telephoto... great for portraiture, among other things where that type lens is useful. On APS-C cameras an 85mm lens is a good complement for a 50mm... covering the "ideal" portrait range. Besides their focal length, angle of view and the way these lenses render a natural looking perspective another factor is that they are available with fairly large apertures: f/2.0, f/1.8 and f/1.4 versions are available for reasonable prices. In the Canon line-up, more premium priced f/1.2 are also available. These large apertures can be used to fairly strongly blur down backgrounds, which also can be desirable for portraiture, among other things.
On APS-C cameras... 50mm is sort of an "indoor portrait" and 85mm sort of an "outdoor portrait" focal length. Of course their uses in either situation depends upon what working distance you have and how tightly you're trying to frame your subject. 50mm can be nice for portraits of couples and small groups. And 85mm might be a good "head and shoulders" lens.
Macro lenses also tend to be short telephotos, though most 50mm and 85mm are not particularly close focusing to offer high magnification on their own. However, they can be used with macro extension tubes relatively easily. The longer the focal length, the more extension that's needed to make significant changes in a lens' close focusing ability. Therefore, a short teles such as these might also be pretty easily used in combination with macro extension tubes.
There are some 50mm, 70mm and 90mm macro lenses. But most macro lenses offer no larger than f/2.8 aperture... That's not bad but one to two stops less ability to blur down backgrounds, and really do no better than match some premium zooms with f/2.8. I've been using one lens that's a bit of an exception... Tamron SP 60mm f2.0 DiII (crop only). In a sense this replaces replaces 50mm, 85mm and a macro lens in my camera bag when I want to travel light. One lens instead of three is great, although my 50/1.4 is still a stop faster. The Tammy 60mm is also rather slow focusing (like most macro lenses) so certainly isn't a "sports" lens. But it tucks nicely into one corner of my camera bag.
Of course, low light shooting is another possibility with these "fast" lenses. Also, primes such as these are much more compact than many zooms, especially when compared to fast premium f/2.8 zooms. These primes may be less intrusive and intimidating to subjects... maybe less likely to get the attention of a mugger, too.
In the Canon lens line-up the "portrait pair" (50mm and 85mm) can be complemented with 35mm f/2.0 "standard" lens and 28mm f/1.8 "slightly wide standard" (on APS-C). There are also premium 35mm f/1.4 and 24mm f/1.4, if you're okay with their price, size and weight. Or, if you want stronger telephotos there are the 135mm f/2.0 and 200mm f/2.0... though these certainly bigger and heavier too. Wider and longer focal lengths both render perspective less naturally than the short telephotos. You particularly have to be careful of wider lenses used to close or with subjects positioned near the edge of the image area, as these lenses will tend to exaggerate perspective quite a bit. Longer focal length effects on perspective are more subtle and can even be desirable for things like fashion photography. OTOH, a 28mm or 24mm can make for a good "environmental portrait" lens... capturing a person within their workspace or home in a more photojournalistic way, showing some of their surroundings to "tell" more about them. Conversely, an 85mm or 135mm on APS-C can be a "candid portrait" lens, allowing you to shoot from a greater distance to be less intrusive with the subjects.
Most of these lenses have very fast USM focus drive, too. That's great for sports, if you can work close enough. It's generally not great for video though (switch to manual focus instead... or use an STM lens).
A couple of these lenses also have image stabilization (35/2.0 and 200/2.0). I suspect we'll see this feature added to more of these primes in the future, though it does appear to increase the cost of a lens $100 to $200.
There are few "negative" aspects of using these lenses... Working with primes usually means carrying more lenses and they're less convenient than zooms. You'll need to learn to "zoom with your feet". Also, the large apertures they offer tend to be more demanding of accurate focus. Shallow depth of field is less forgiving of any focus error. Some people just can't give up their zooms... and there can be times even for portraiture when a zoom is desirable (kids and pets, for example).
It's good to experiment with primes and see how they work for you. I think primes promote good habits of walking around your subjects and looking at them from different distances and angles.... While zooms do the opposite by encouraging you to stand in one place and rely upon the lens "do the work".