What does a single-lens reflex camera mean? To put it simply, I can’t understand what it says in the encyclopedia. What is a double-lens reflex camera? Which one is better? Can you take selfies?

1. What I understand as an SLR is that the light reflected by a lens is used to frame and image the image. Ordinary digital cameras (we call them "card cameras") have no reflectors and can only convert electrical signals to the LCD screen. The lens is used for framing, so although it is also a lens, it does not reflect light for framing. This is the optical difference between SLR and card cameras.

2. What I understand as a dual-lens reflex camera is that one lens takes the view and another lens creates the image. It's relatively rare.

3. Digital cameras can all take selfies, it just depends on the angle when holding them with your hands. Regardless of SLR or card, if you want to take good selfies, buying a tripod will solve the problem. Every camera should have bolts for attaching to the tripod, and the tripod has nuts and a quick release plate for connecting the camera. After setting the time, you can take pictures however you want.

4. Thinking of the "double mirror" question you raised, if you want to ask if there is a camera with front and rear lenses like a mobile phone to facilitate selfies. I haven't seen it.

I think the above 4 points can probably explain your problem. If you can’t understand it, there’s nothing I can do. I hope there are experts who can answer your questions in detail, but the experts are busy creating or busy writing. Nothing else.