Your problem description is:
Why is the camera just a lens?
Let's answer this question first.
This is my camera, Sony A6700, an APS-C camera.
As you can see, it does only have one lens now, and it is currently equipped with Sanyo's AF 75 18. Don't ask me why the lens cap is Canon's, because I'm rebellious.
The reason is because when I went to shoot outdoor portraits before, a medium telephoto large aperture lens was more suitable.
But actually, I'm not the only one that I can have on hand to fit this camera.
From left to right, in order:
e pz 16-50mm f3.5-5.6 OSS, which is also the lens of the Sony suite, is known as the 16-50mm f8 GM.
30mm f1.4 DC DN, one of the Sigma Three Musketeers, is very easy to use.
Next up is the Sony FE 35mm F18, This is a full-frame lens, don't ask me why I have it, because I still have Sony's full-frame body.
On the far right is, 17-70mm F28 DI III-A VC RXD, this head is very easy to use, and the product portrait can be shot.
I also have an adapter ring for the EF-E port, which looks like this.
In other words, even if it is not a Sony E-mount lens, it can be used through this adapter ring, and I still have three EF lenses on hand.
They are: Sanyo 14mm F28 ultra-wide-angle lenses;
Sigma 35mm F14 art：
Tamron SP 70-200mm F28, show you this head shot**:
So, the camera doesn't just have one lens, it can fit an infinite number of lenses if you want.
If you have to say, although there are many camera lenses, you have to change them, not necessarily, because some zoom heads do not need to be changed, such as the 16-50, 17-70, and 70-200 I mentioned above, the same lens, you can get the zoom effect by twisting it.
If you have to raise the bar, the zoom lens is also a lens, and the camera can only be loaded with one at a time. Not really.
As you can see, this kind of camera, one camera has two lenses, and its name is double-reflex, yes, it is the double-reflex that corresponds to the single-lens reflex.
This kind of camera shoots ** is also very exciting.
Shot with Kodak Protra 160.
It is possible that if you know this model, you will say that this kind of camera is actually used for framing with one lens and one camera for imaging, which is not counted.
Actually, it's not, let's take a look at this machine, all three lenses are used for imaging.
However, this kind of camera shoots stereoscopic **.
Is there a four-shot, there is!
The former shot four films at once, and Kodak was overjoyed;
The latter can be ** four pictures on one negative, and Kodak laughs less obviously.
So, in the problem description, the camera is just one lens is wrong.
Let's answer again, why do mobile phones have four lenses or more?
If you've ever taken photos with a contemporary phone, you'll understand that the existence of multiple cameras is actually to give you more focal length.
Usually it is a combination of ultra-wide-angle, wide-angle, and telephoto.
But the range of telephoto is very wide, sometimes one is not enough, just one for the medium telephoto, and another for the telephoto, such as the Xiaomi Mi 13ultra is such a configuration.
But sometimes this combination is not enough, so in order to achieve better sensitivity, a black and white camera was added, and for better bokeh, a depth of field camera was added.
There are also a number of macro lenses, in fact, they can exist as an independent lens.
Generally speaking, as long as a mobile phone has used its multi-camera system to shoot**, or to search for introduction, you will know what each lens is for.
If you still don't know, it's most likely for two reasons:
1.Your level of comprehension is already far behind this era;
2.The look of multiple cameras on your mobile phone is not even a tactical lens, we generally call it an ornament, and it is common on copycats.