Sometimes advice is good and bad simultaneously. Good when it helps you consider something you might not have considered before. Bad when it’s conveniently followed without further thought.
Like in a previous posting, this is a story about a tip often heard, a common advice on forums and in real life. Well, not so common, because it’s exclusively about lenses with a fixed focal length.
Perhaps a first question would be why one wants to shoot a fixed focal length anyway. Why restrict or limit yourself, while zoom lenses are readily available? That question, a good one, deserves a separate post, though. Not today. For the sake of this post, just take it that there are good reasons to shoot prime lenses. The question is not ‘why’, but rather ‘which one’.
A not too uncommon question from relative beginners is “which prime should I get?”. The answer to that is really a question about focal length. And more often than not, people overlook a bit the impact of such a choice.
A particular point of view
As I argued before, the choice for a particular focal length isn’t just about how much you get into the view, or the opposite, how much you want to exclude from the frame.
It also changes the apparent distances between items in the background, and items in the first plane. Wide angle lenses will make them seem further apart, while telelenses seem to bring them into a single plane.
This changes the relationships between elements, and that may change the story your photo is telling. It can also change the atmosphere. With the larger distances of a wide angle, there is also less sense of intimacy, closeness. Telelenses may exaggerate that on the other hand. Or, wide angles used from very close distances, may give a very much in-your-face or a sense of being there in-the-moment. Very intimate, or maybe plain invasive.

My already confessed favourite focal length is 50mm, and I count this above 58mm as being basically a 50mm with a dash more intimacy.
How to choose primes?
If you prefer to work with primes over a zoom, then how do you select the focal lengths? Of course, if you bank account and your backmuscles agree, get the lot of them, bring them all and you got everything covered. But quite often, the point of shooting primes is that they’re smaller and lighter. So you might want to carry 2 or 3 of them. How do you commit to two focal lengths?

My honest advice here is always to start with a zoom lens. The lenses supplied with most cameras (‘kitlens’) tend to cover a massively useful range. They start at a wide-ish angle (24 or 28 mm in full frame / 35mm film), and end up at the short tele range (70 to 85 mm). In that range, we find the classic focal lengths that have been the staple for ages: 35mm, 50mm, and wider and longer.
Fashion
This last bit might be an old-fashioned look at it. In the last decade or so, there has been a trend towards wider and wider angles. That is probably part due to the increased quality of wide angles lenses, but also it’s more and more fashionable. So perhaps 35 and 50 aren’t the staple anymore.
Frankly, I don’t care, since I don’t care about fashion in any shape or form. What has always worked well, will still work well. Just because the current idea pushes us to prefer something else, doesn’t mean it’s a right idea. And next season, the fashion might change anyway.

So, anyway. Take that zoom lens, and try the to deliberately shoot using only 35mm (or its equivalent, for example around 23mm on APS-C) for a day. Then do the same again, but using 50mm equivalent. Get familiar with those two, and get familiar with the differences between them.
That’s just the start of the discovery: you may find you don’t like either. Maybe 35mm feels unnaturally restricted, not wide enough. Then clearly you gravitate to wide angles – follow up with your zoom, and test it at its widest. Or maybe 50mm feels OK, but a bit to loose. Zoom further in, and go from there.
Point is to find that focal length that connects for you. There is a length that feels completely natural to you, and that feels completely logical when you’re using it. That’s the one you want.
The Goldilocks option
Not too wide, not too long. Just right, like Goldilocks and those 3 bears. Now that focal length is the one to get the best lens you can.

But having just one focal length might be a big limiting. So what makes sense beyond this one centre piece in your lens bag?
The advice that is often given, is to half the focal length, and double it. That leaves you with a trio that will cover most of your needs. Unless you’re already at the ultra-wide end, or the supertele realm.
Two common series you get then are : 28mm – 50mm – 100mm, and 24mm – 35mm – 75mm. And to me, these two series make a lot of sense. Like a serious big lot of sense. The underlying logic in these two series does add up, and in practical use you won’t feel left wanting (again, unless you’re into extreme wide angles or telelenses and superteles).
Except…
You should trust your gut. It is something hard to put in words, or images. But the moment you raise the viewfinder to your eye, a focal length makes sense of not. It feels good, or not. And not in the way that it’s the right choice for the scene in front of you, but in the sense that it feels right.
Those two default line-ups mentioned above are worth considering. But get that zoom lens out, and test it for yourself.

Given my preference for 50mm, my logical wider option would be 28mm. And as displayed above: that is what I have. There were other reasons involved in getting this 28mm, and it is a spectacular performer. A lens I really cannot flaw.
And yet I struggle a bit with it. It’s too wide for me for casual use. I’m not a wide-angle type, and 20mm is completely wide enough for me as ultra-wide. As a normal wide, 28mm is just a bit too much.
That is not all a bad thing; it’s a lens that forces me to think a bit more about composition, because it doesn’t come naturally to me. That’s not a bad thing. But I often end up disliking the converging lines due to the perspective a bit. It’s just not natural to me.

That’s just me; it’s not the lens’ fault. If any fault at all, it would be mine, for buying it in the first place. Because I knew 35mm works for me.
It’s too close!
You may hear people telling you it’s too close, and 35 and 50 are almost the same thing. Maybe that’s true, for them. It sure isn’t for me. That’s the whole point: it has to feel right. To me, to you, to whoever uses it.
Because selecting a prime for intensive use is a commitment to a focal length. It has to work for you, feel good, logical and natural. Deliver the images that make you feel good.
Get a standard zoom, and get a feel of what works for you. If you’re just starting out, those kit-lenses are really a good point to start, even if it is just to show the directions. And beyond that, trust your own guts. You know when you look through the viewfinder what you want, and how. Don’t let others or fashion tell you otherwise – it is your personal creativity, not theirs.

If you decide to work with primes only, it helps a lot if you have this mental projection of how they will work for the scene. You’ll blindly know which one to grab, rather than wasting time on trying to decide what will work. That makes primes satisfying to use.
So, what prime should you buy? The one your zoomlens tells you to buy. Yes, it really is that simple.