Is the shoulder camera bag divided into two layers or a single layer?

It depends on how many people you have.

Generally speaking, a camera bag with an article compartment is convenient for carrying some personal belongings, but it can hold less equipment than a pure equipment camera bag under the same volume.

Especially when you have such a large lens as 70-200, a single-layer camera bag can hold it, but with the goods compartment, the equipment space at the lower level often can't hold it.

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It is suggested that if you need to carry a telephoto lens, choose a single equipment backpack.

If there is no bigger lens, you can choose which one at will.