What is a DSLR?

I just answered a similar question today. It’s too long, so I’ll turn it around.

100% original by me.

I was chatting with a friend a few days ago and said that many people who are interested in photography nowadays and talk about SLR every day actually don’t know what SLR is. After reading the answers from the two people above, I feel like this is indeed the case. If the answer on the first floor is copied and pasted, it seems that this problem is more common. In order to prevent mistakes from spreading, let me explain what SLR is.

SLR (here we only talk about cameras, not tennis), the double literal explanation is "single lens reflex camera", referred to as SLR. The English abbreviation SLR. When this term was invented, it was still the film era, so it has nothing to do with digital. Since the definition does not involve what kind of photosensitive material is used, whether it is a digital SLR today or a film SLR in the early years, it is a SLR. But later, in order to distinguish it, a D was added in front of SLR, and DSLR refers specifically to the current digital SLR.

SLR, single-lens reflex camera, the single lens here is relative to the dual lens.

When the term was invented, double-crossing was still very popular.

Twin-lens reflex camera, that is, a twin-lens reflex camera, has two lenses, one is responsible for framing the view, and the other is responsible for sensitizing the film to complete the shooting.

(Reflective type will be explained later)

SLR cameras have only one lens, and framing and exposure of the photoreceptor (whether it is film or CCD/CMOS) are all through this lens.

How to do it? This is about "reflective".

Let’s talk about the “reverse” of “double-reverse” first.

In a twin-lens reflex camera, the upper lens is responsible for framing the view. The light passes through the lens and shines on a fixed 45-degree flat glass mirror behind the lens, so the image that directly enters the viewfinder lens turns upward and is projected on On the frosted viewfinder glass, the photographer can compose the view and observe and adjust the focus.

The reflex of a SLR is similar to that of a double-lens reflex. There is a 45-degree flat glass mirror behind the only lens, but this mirror is not fixed, but movable. It is usually there at 45 degrees, redirecting the light entering the lens upward, through the pentaprism (explained below), and into the viewfinder. The moment you press the shutter, the small mirror (called a reflector) will pop up and flip up. This opens up the light path and allows the light entering the lens to directly enter behind the reflector. At the same time, the shutter opens to expose the photoreceptor and make it sensitive to light. After the exposure is completed, the reflective lens automatically resets and the light is introduced into the viewfinder.

This is also the reason why when we use a SLR, the viewfinder will go dark the moment we press the shutter.

Since the SLR uses the same lens for framing and shooting, the reflector must be movable and switch the light path during framing and shooting.

The reflector of a double-lens reflex camera is fixed, because it has its own lens for framing and shooting without interfering with each other.

However, double-lens reflex cameras are large in size, require the same two lenses, and the cost of the lenses is high. The most important thing is that due to the two lenses of framing and real shooting, there is parallax, which is more obvious especially when shooting things at close range. What you see may not be exactly the same as what you take.

What you see is what you get with a SLR (the viewing range is not discussed here). The camera is relatively compact, but the camera shakes when the mirror is turned up and down, which sometimes affects the image. More than 80% of the clicking sounds we hear when shooting are not the sound of the shutter, but actually the sound of the mirror moving.

An important feature of SLR cameras is that the single lens can be removed and replaced.

Finally, let’s talk about the pentaprism.

Originally, this content has little to do with explaining SLR.

But Lou mentioned it, and there are errors, so it is necessary to correct it.

Let’s talk about double reverses first.

Twin reflex cameras only use a 45-degree mirror to reflect light onto the viewfinder screen. We know that the mirror image is reversed,

So when we hold the camera and lower our heads to view the view, The images seen on the frosted glass are also reverse images.

If you move the camera, like asking the person on the left to click to the right, in the middle of the screen, what you see on the screen and the actual hand movements should be reversed. This makes operation very inconvenient!

So a five-sided corner was designed on the reflector of the SLR camera. Its function is to make what we see in the viewfinder appear to be positive, up, down, left and right, after multiple reflections. Direct viewing is consistent in all directions.

SLR cameras are all big cameras, with a pentaprism inside.

Some low-end SLRs released recently use pentamirs instead of pentaprisms, which have the same effect.

In addition, one more correction: the image seen in the viewfinder of a SLR camera is inconsistent with the image seen on CCD/CMOS and film.

CCD/CMOS/film looks like it is upside down, but we can’t see it in the camera. After taking it out from the camera, we just need to “turn it over” and we will see the upright image.

The second floor explains the reflector as a "mechanical reflector", that is, a mechanically moving reflector. This is only an explanation for single-lens reflex cameras. It does not take into account the existence of dual-lens reflex cameras and ignores the continuation and coherence of knowledge.

Also, the reflector of the EOS RT and the latest Sony a55 in the film era is translucent. When the translucent reflector is illuminated through the lens, part of it is reflected to the viewfinder. At the same time, , the other part penetrates through and shines on the shutter, just waiting for the shutter to open to expose the photoreceptor. Therefore, this translucent reflector is fixed.

Another extension:

Single camera, this is a new name, relative to SLR. Single lens electronic viewfinder camera.

Generally written as EVIL (Electronic Viewfinder Interchangeable Lens).

Its features are the same as those of a SLR in that the lens can be replaced, and this lens can only be used for framing and shooting.

Just the light entering the lens is directly projected on the CMOS and converted into electrical signals, which are then played out in real time on a special viewfinder or the back LCD for framing. Press the shutter button and take a screenshot to complete the shooting.

Replacing machinery with electricity should be the general trend.

However, single-voltage batteries have not started for a long time, and it is still difficult to compete with single-voltage batteries in all aspects.

Sony calls its single-lens camera NEX5 a "micro-single camera". From this point of view, it can be seen that it is unprofessional.

Micro, what counts as micro? Isn’t a half-frame camera smaller than yours? Isn't the 110 camera smaller than yours? Not to mention MINOX.

In no words, they are all a mirror.

Mirrorless cameras are far inferior to single-lens cameras, which shows the characteristics of this camera.

Further addition:

Aunt Thirteen should be the one in the Once Upon a Time movie, right?

I have some impression of the plot of the movie, but I can’t remember it clearly. Is she using a double reverse mirror?

Still a "non-reflective" camera?

I have already said so much, but fortunately I will say a little more.

Earlier cameras did not have reflectors.

The camera structure at that time was also very simple, just an opaque box and a lens.

Attach a movable panel behind the black box, and usually place a piece of frosted glass.

When taking a picture, open the lens cover, let the light enter the camera obscura, and form an image on the ground glass (focal plane).

This seems to be completely upside down, and it is very difficult to watch!

During the day, you should also cover your head with a piece of black cloth, otherwise the frosted glass will be too bright and you will not be able to see clearly.

After taking a good view, insert the film box in front of the frosted glass. At that time, the film was not in rolls, but in sheets.

Early cameras didn’t even have a shutter, and the film’s light sensitivity was poor.

As long as you take off the lens cap, and according to experience, put it back on after a few seconds, the photo will be taken.

How do I remember that Aunt Thirteen used this kind of camera? I can’t remember clearly, I’m not sure.

The double-lens reflex camera is the Seagull 4 camera from China in the 1960s and 1970s. It is a typical double-lens reflex camera.