What Does SLR Stand For?

The term SLR, although commonly heard, still seems a bit elusive as far as just what does SLR stand for?

Single-Lens-Reflex.

What does this mean?

Simply put a Single-Lens-Reflex camera, whether it's film or digital, will have features not found in a compact point-and-shoot.


What kind of features?



Two unique features

You can change lenses, allowing for greater creativity and choice of lens depending on your subject.

You can actually view your subject through the lens.

In addition, there is often the option of overriding the automatic controls, which allows you to control the creativity of each photo.

View through the lens?

Yes. This lets you make adjustments to your composition because you see the same image as your sensor or film.

You may be thinking, "how can this be?"

Simply put. As you view your subject the scene is reflected off a mirror, which is inside your camera, to your eye.

Depending on the camera features you may see closer to 95 to 98% in the end result of your photographs. Meaning, as you look through the viewfinder you're not seeing exactly 100% of the scene.

To note. In the case of film cameras, some SLR models are completely manual meaning the photographer needs to adjust all of the settings while some are totally automatic. They still relate to what does SLR stand for, however.

More about what does SLR stand for and focusing through the lens.

In front of where the digital camera sensor is situated, or in front of the film, there is a movable mirror.

This mirror sits at a 45 degree angle and when light hits it the light is refelected upward until it eventually comes out the viewfinder. Also being reflected is the image as it appears, meaning it's reflected to give you a correct left to right and upside right image.

However, because images are recorded when light hits the sensor, or film, there are some clever features to keep everything working as it needs to.

For one thing, most of the light is reflected in an upward direction to the viewfinder, by the mirror.

In addition, on most SLR's there is a shutter right in front of the mirror. Cleverly enough, when the shutter is closed no light can hit the sensor. This shutter is called the focal-plane-shutter because it is situated right in front of the sensor or film.

Why don't you want light hitting the sensor?

You do because this is how the image is recorded but you only want it when it's time to actually take the picture.

How does this work?

Amazingly enough, the mirror is hinged. So, if you recall, there is no light hitting the sensor because of the shutter which stays closed most of the time.

When you press the shutter-release button in the act of taking the picture, up goes the mirror to get out of the way, the shutter opens and light now reaches the sensor or film. Presto, you now have your image recorded by the light hitting the sensor. Wow!

Another thing as what does SLR stand for is being investigated.

Have you noticed, however, if you have a SLR, that when you press the shutter-release button you cannot see daylight in the viewfinder?

Faster than you can say what does SLR stand for, so only for a "blink of an eye" can you not see daylight and sometimes that's long enough to cause a problem. Have you looked at photos of people only to realize your subject literally blinked their eyes and you're photo shows them closed?

Another challenge could be in determining if your flash fired properly.

I expect you've noticed your SLR makes a noise when it takes the picture. I happen to love the sound but there are times it's not appropriate. This noise is caused by the mirror moving up out of the way. Once again, as we examine what does SLR stand for this is yet another minor challenge.

Relating what does SLR stand for to vibration from the mirror.

Most of the time this is not an issue but it is something to be aware of. It becomes more of a problem when using a slower shutter speed and also when using a long lens.

In the big picture of things mirror vibration is not usually a problem and using a tripod will, of course, help control camera shake.

What does SLR stand for and another clever feature already touched on but worth clarifying.

Focusing through the lens also means you can use the viewfinder as a focusing screen. This works because when the subject is brought into focus by you it's also then in focus for the subject.

Now that you know what does SLR stand for, Single-Lens-Reflex, there is also a Twin-Lens-Relfex although that's for another day.

One more what does SLR stand for feature as it relates to viewing your image and aperture. Aperture is also referred to as f-stops and f eight is written as f/8, for example.

Before reading about aperture you may want to scroll down to view the sample diagram, the one with the circles. There's more information, later, regarding aperture as it relates to a fast lens.

When thinking about aperture, in a nutshell, the smaller the number the greater the amount of light entering the lens, the greater the number, the smaller the amount of light. So, f/4 allows more light than f/16.

Let's pretend you want to take a picture with your aperture set to f/16. Just like the sample in the diagram further down the page f/16 is telling us that not much light is entering the lens. Also remember, in reading what does SLR stand for, is the ability to view your subject through the lens with help from the viewfinder.

If you think about this, how much light would there be entering the lens at f/16 compared to f/3.5? If you said not much, you're right. If you're not sure have another look at the circles depicting aperture openings.

Let's tie this together with the ability to look directly through the lens. If f/16 does not allow in much light does it stand to reason you would also expect to see less light through the viewfinder and therefore composition and focusing would be a problem?

Yes? Right again.

So what is going on?

Cameras are certainly amazing and this is yet another example of just how amazing.

In a nutshell, the camera shows you the subject through your lens and thus the viewfinder. In determining what does SLR stand for this focusing feature is applicable.

It also shows you the the brightest possible subject.

This means your lens will always show you the image relative to the largest aperture available, according to your specific lens.

If you look on your lens you will find some very helpful numbers telling you what the lens capability for wide open aperture is. If you're confused, scroll down the page until you see two pictures showing numbers on the lens.

The number(s) on your lens(es) are giving you information about the largest aperture. Remember, the smaller the number the larger the aperture and the greater the amount of light entering the lens.

Let's say the number is f/3.5. When you look through the viewfinder your camera is giving you an image relative to the f/3.5 amount of light. Nice and bright so you can see what your seeing. The benefit of this amazing feature is you get to see your subject in the brightest possible light which makes composition and focusing as easy as possible.

Surely there must be some what does SLR stand for magic to this? There is!

Going back to the f/16 reference. When you press the shutter-release button this triggers the lens to "stop down", in other words close the aperture to f/16.

In the split instance of taking the picture the diaphragm of the lens stops down, or closes to f/16 and then opens again to its maximum aperture, in our example, f/3.5.

Just think, this happens every single time, no matter what you have the aperture set on. Whether it's f/5.6, f/8.0 or f/22 your camera and lens have this diaphragm system all figured out!

Due to the lens interchangeability dust on the sensor can sometimes become a problem. Again, this is just something to be aware of and to be careful and mindful of conditions when switching lenses.



More about light hitting the sensor as a focused image for a specific period of time.



Briefly, what does specific period of time mean?

As the photographer, it's whatever you determine or else whatever the camera determines if you're using the automatic exposure system. In other words, the auto setting.

Have you seen photos in magazines where the caption refers to the photographer using a long exposure, in some cases hours?

In comparison, think how quickly your camera can take a photo on a bright sunny day. "Click", done, or so it seems.

Specific period of time is, quite simply, how long it takes for the camera to record the image.

This is controlled either by you or the camera, if in automatic mode and referred to as shutter speed.

What does slr stand for and back to the compact point and shoot for just a second.

In comparison, there is no mirror to "reflect the scene and flip up" and you cannot change lenses.

Cameras which do not allow for lens changing are referred to as fixed-lens cameras.

Also, when you compose your scene using the point and shoot viewfinder, if your camera has one, you're actually looking through a glass window.

This means you will not see exactly what is being seen by the film or sensor because you're not looking through the lens.

Does this techno sounding stuff make a difference to your photos?

That all depends.

If you're a photographer who understands the features of your point-and-shoot, along with a good foundation of how to take good pictures, I expect you're getting some shots you're happy with.

Comparitively, the most expensive SLR with extra doodads and tons of lenses will not a photographer make, at least not without knowing a few basic photography tips and camera functions.

That being said, the SLR camera is a lot of fun, certainly offers more features and a wide range of opportunity beyond the compact camera's capabilities.

Getting back to what does SLR stand for.

As mentioned above, Single-Lens-Reflex cameras allow you to change the lens.

Why would you want to do this?

Depending on the lens you purchased with your camera it may have limitations for what you wish to photograph.

Limitations could be things like distance from your subject, such as wildlife, when you need to stay a good distance away for both your safety and the subject.



Perhaps you've just purchased a new fun lens, a macro or zoom and can't wait to use it.

Maybe you realized the benefit of having a faster lens.

A faster lens means how much light can the lens transmit, or in other words, how much can it let in?

Do you remember the information about the lens stopping down to f/16 even though the viewfinder shows us a larger aperture at f/3.5, for example?

Now you know a bit about what's happening with aperture and this is leading into what's meant by a fast lens, which I'll get to right after this.

A digital SLR allows for greater creativity as you can select the lens you want depending on the subject and situation.

By now I'm sure you have a sense as to what does SLR stand for...

Interchangeable lens capability and the ability to view the scene and focus the image directly through the lens. The result of the mirror reflecting the scene to you.

More about the lens in a minute as this as good a time as any to mention camera shake.

There may be times when you're fooled into thinking your photo is out of focus and it's not.

Now that you're aware of what does SLR stand for and if you have this type of camera, I'm sure you've noticed some lenses are heavier than others.

Also, depending on the zoom capabilities the lens may extend quite a distance from the camera body.

Include a slow shutter speed, which is different from lens speed and it's easier than you may realize to create camera shake.

Because the lens is related to what does SLR stand for, simply in being interchangeable, let's take a look at

what the lens is telling you.

Return from What Does SLR Stand for to the Beginner Photography Guide.

Return from What Does SLR Stand for to Index SLR Digital.

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