Definition of SLR: I always thought that a camera with a thick body and a long lens was a SLR.

Let me give you an accurate definition and explanation.

SLR, literally means "single lens reflex camera", referred to as SLR. English abbreviation SLR. This word was invented in the movie era, so it has nothing to do with numbers. Because the definition does not involve the use of any photosensitive materials, both digital SLR and film SLR in earlier years are SLR. Only later, in order to distinguish, a D was added before the SLR, and DSLR specifically refers to the current digital SLR.

"Single lens" in the definition of SLR is relative to double lens.

When the word was invented, double opposition was still very popular.

Double-reflex camera, that is, dual-lens reflex camera, has two lenses, one is responsible for framing and the other is responsible for film exposure to complete shooting.

(Reflective type will be explained later)

SLR cameras have only one lens, which is used to view and expose the photoreceptor (whether film or CCD/CMOS).

How? This is about "reflection".

Let's talk about the "anti" of "double opposition" first.

Double-reflex camera, the upper lens is responsible for framing, and the light passes through the lens and shines on the 45-degree plane glass mirror fixed behind the lens, so the image directly entering the framing lens is turned upwards and projected onto the framing ground glass for photographers to frame and compose, and observe and focus.

The reverse of a SLR is similar to the reverse of a double-reverse. There is a flat glass mirror with a 45-degree angle behind the only lens, but this mirror is not fixed, but movable. Usually, it exists at an angle of 45 degrees, so that the light entering the lens goes up, passes through the pentaprism (which will be explained in the next article) and reaches the viewfinder. The moment you press the shutter, this little mirror (called mirror) will bounce up and turn over. In this way, the light path is unblocked, so that the light entering the lens can be directly injected into the back of the reflector, and at the same time, the shutter is opened to expose the photoreceptor and make it sensitive. After exposure, the reflective lens will automatically reset and introduce light into the viewfinder.

This is why when we use SLR, the viewfinder will be black at the moment when we press the shutter.

SLR camera and shooting * * * use the same lens, so the reflector must be active, and the light path should be switched when shooting and shooting.

The double reverse is fixed, because both framing and shooting have their own lenses and do not interfere with each other.

But the double mirror is bulky, the lens is the same as the other one, and the lens cost is high. Most importantly, because of the parallax between the two shots, it is more obvious to shoot things at close range, and what you may see is not exactly the same as what you shot.

SLR is almost what you see is what you get (the scope of framing is not discussed here), and the camera is relatively small, but when you flip the mirror up and down, the camera will vibrate, sometimes affecting the imaging. More than 80% of the clicks we heard when shooting were not the sound of the shutter, but actually the sound of the mirror moving.

Another important feature of SLR cameras is that this single lens can be disassembled and replaced.

Finally, let me talk about the pentaprism.

Let's talk about double opposition first.

Double reflection only uses a 45-degree mirror to reflect light onto the viewfinder screen. We know that mirroring is the opposite.

So when we look down with the camera, the image we see on the ground glass is also inverted.

If you move the camera and want the person next to you to move to the middle, what you see on the screen should be the opposite of the actual hand. This makes the operation very inconvenient!

Therefore, a pentaprism is designed on the reflector of SLR camera. Its function is to make the image we see in the viewfinder positive, up and down, left and right, which is consistent with direct vision in all directions.

The SLR camera head is very big, and it is a pentaprism.

Recently, some low-grade SLR have replaced pentaprism with pentaprism, and the effect is the same.

One more thing to clarify is that it is said that SLR imaging is good, but this is not directly related to the word "SLR".

The difference in imaging quality between a lens the size of a coin and a lens the size of a barrel is fundamental.

And the most fundamental thing is the size of negative numbers.

The CCD/CMOS of a small card machine is actually only the size of a fingernail.

The CCD/CMOS commonly used in digital SLR cameras is the size of stamps.

I have just calculated that the CCD area of the most common APS-C (small, non-Quan Huafu) SLR is 9.857 times different from that of the larger11.8-inch card machine (high-end card machine of about 3,000 yuan). About 10 times!

Not to mention the ordinary thousand yuan small card 1/2.3 inch compared to the full-frame machine.

So the main reason for good SLR imaging is that the frame is relatively large and the lens quality is high.

In fact, there are many factors such as advanced processors.

A "big guy" like Fuji S 100 just looks like a SLR, but it doesn't have the mirror and pentaprism of a SLR camera. So I call this camera "Big DC". Not a SLR.

If you have any questions, please ask.