Why is the lens hood of the SLR partially flattened?

This problem needs to be discussed from the lens of a DSLR camera, the characteristics of the focal length are that the shorter the focal length, the wider the field of view, and the longer the focal length, the narrower the field of view. With this in mind, let's talk about why the hood is not uniformly round, but has to be "flattened" in a certain part. When we use telephoto, due to the optical principle of the lens lens, your target scene will be magnified, so that the field of view will be narrowed, at this time, what kind of hood will not have any effect on the lens framing, but when you zoom to a wide angle (when the focal length is short), also due to the optical principle of the lens lens, so that the field of view you get wider, at this time, if you continue to use the lens hood of the telephoto lens, the edge of the hood will appear in the frame. At this time, it is necessary to make conditional modifications to the hood, which is the appearance of what you call "flat".

For example, if you have a 35-135mm end, and when you shoot at the 135mm end, it doesn't matter if the hood is all cylindrical, because the framing will not be affected, and when you are using the 35mm end, the field of view will be wider, and the hypothetical 135mm cylindrical lens hood will leave a black shadow in your viewfinder, as is the case with a pinhole camera, and then we will have to modify the hood. In addition, the shading sheet is generally protruding at the upper and lower ends of the lens, and only at the left and right ends of the lens is "flattened", you will find that there is only one effect of this, that is, the distance between the upper and lower fields of view will not change greatly, and the left and right sides will get a wider field of view distance, which is basically caused by the rectangular shape of our film or digital imaging system.

Because the sensor is rectangular, the front cover can be made flat.

The purpose of the hood is to mask the light to the maximum extent without affecting the angle of view of the lens. You don't need to know the principle. If you understand the function, you can understand the problem of shape. There's no need to look into that.

Because the angle of incidence of light is different.

Let's take a look at the lens description, some lenses and cameras don't match exactly.

Don't pick up points, posting is pure sympathy. Go to the Canon Repair Center. Tell them to go to school.

Just take a few more shots of the object and compare it.