40mm vs 50mm Prime Lens

A lot of people will look at the focal length of 40mm and 50mm and ask, “What’s the difference?” Because they seem so incredibly close to one another.

This blog is not to say which one is better. Each lens has its own time and place where it can shine.

*For this blog, I’m going to be talking about the Canon versions and I’m not going to talk about the L-Series since those are on a more professional level and the EF versions are much more common.

Let’s talk F-Stop

It’s one of the first things you can see for these lenses. It’s literally right on the box, or online, the title of the lens.

EF 40mm f/2.8 STM

EF 50mm f/1.8 STM

f/2.8 is more than double the amount of light as f/1.8. I know it doesn’t make sense to say it like that, but every full f-stop doubles the amount of light. From f/2.8, the next full stop up is f/2. f/1.8 is 1/3 of a stop up, so you’ll get 133.33% more light with a 50mm lens than a 40mm.

If that’s too much math, just know that a 50mm Prime lens will give you more light and a shallower depth-of-field, should you choose to use it. As with all lenses, you can stop down to whatever you want out of what’s available to you. They mostly go very, very low.

f/2.8 is still very, very wide, so that’s usually not an issue for the standard user. If you’re wondering how shallow f/1.8 is, it’s very shallow. In a portrait situation at that aperture, the lens could be focused on the tip of the subjects nose and the middle of the nose will be blurry. Even using f/2.8 in the same situation will cause the eyes to be blurry, which is incredibly shallow as well! Most people can’t tell the difference. Here’s an example!

This first silly photo was taken with a 40mm lens at the widest aperture.


You can see that it’s fairly shallow. The tip of my nose is in focus, but my eyes are a bit blurry. You can also see that my head is a little too big for my body. That’s because of the slightly wide angle of the 40mm lens, but that’s for the next section.

This next picture is very special to me, since I took it the last time I ever saw my grampa. It’s also the best photo example I can find while writing this.


You can see that his eyes are in perfect focus, but the image begins to blur just barely into his nose.

What’s Bowing?

Bowing is a change in an image based on the focal length of the lens. It is present in the images above, as I mentioned. The image of my grampa doesn’t appear bowed because it’s shot at 50mm (what some people argue is the focal length of the human eye), but the image of me is slightly bowed, though hard to see, because it was shot wider than that.

For an exaggerated example, I’ve edited the same image to be at a good focal length and one extremely bowed, or fisheye. These aren’t the 40mm and 50mm lenses, but it’s just to show the effect.

This one is at the original focal length (135mm)


Everything looks proportionate!

Now this one is a fisheye version. I’m not sure about the exact focal length, but we can assume it’s about 8mm.


It’s very disproportionate and looks like you’re looking in the surface of a marble, or through a fish bowl! Hence the term, “fisheye.”

So the 40mm lens has a slight amount of this “fisheye” effect. The 50mm…not so much. It’s closer to what you’ll see with your eyes.

What Can I Use Them For?

Each lens has its own set of uses. Technically speaking you can use any lens to shoot anything. But there are different lenses for different reasons (there may be a blog about that in the future).

But I’ll keep this simple and give you a nice bulleted list for each lens. You can do these things with either lens.

50mm Lens Common Uses

  • Portrait
  • Product
  • Macro

40mm Lens Common Uses

  • Portrait
  • Nature & Landscape
  • Macro
  • Street

They Look Different

Most obviously, they look different! The look is what gave the 4omm its nickname: The Shorty Forty!

Let’s take a look at the two.

On the left, we have Canon’s 50mm lens. On the right, the 40mm.

I listed the 40mm for Street Photography above and not the 50mm. A lot of people will argue that the 50mm is the best for street photography, but I disagree when it comes to a comparison between these two lenses. Great street photography happens when no one on the street notices the camera and the photographer captures a perfectly natural setting. The 40mm lens has such a low profile, barely bigger than the body cap*.

*The body cap is the small protective cover that is used to protect the inside of the camera while no lens is attached.

The 50mm is a little bit more chunky, though still lower profile than standard zoom lenses.

Both lenses can be a little lower profile because they have no moving parts, being Prime Lenses, or lenses that do not zoom.

If a low lens profile is what’s important for you, the 40mm may be your lens! If that doesn’t matter, the 50mm is wonderful!

But What Do They Cost?

This is the final section, so I thought I’d save the big question and shortest answers for this.

I’m only going to list the price directly from Canon’s website because that’s what they cost, regardless of if, “You can get it cheaper on Amazon.” Or wherever else you can buy them.

40mm: $179.99
50mm: $125.99

These are some of the cheapest lenses you can buy outside of off-brand or toy lenses. I bought my first 50mm lens used and it still lasted me almost 7 years. Buying new will last you much longer, assuming you treat it properly (and preferably don’t move every year and across the country like I did).

So there you go! I hope that gives you some clarity as to what lens will suit your needs!

If you have any questions or comments, shoot me an email or leave me a comment below!


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