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What is a DSLR anyway?

What do you think of when you hear the term DSLR? You possibly think of the family camera that collects dust in the computer room. Or one of those large cameras that you see professional photographers using on the football field.

But do you really know how a DSLR works or what those four letters stand for? In this article I am going to go back to the basics and explain where the term DSLR originated from. I will explain the difference between an SLR and a DSLR.  As well as how a DSLR camera works and why they are so important to modern day photographers.


In order to explain what a DSLR is, I am first going to bring us back to analog or film photography. Everything that relates to digital photography can be traced back to film photography. Shortly after the invention of photography, the SLR was invented in the late 1800’s. SLR stands for “singe lens reflex.” Lets break that down so that it actually makes sense and doesn’t just sound like three random words smashed together.

Before the SLR, a camera would have a view finder off to the side of the lens or use a separate lens to view the subject. With a SLR light travels through the lens and hits a mirror that is positioned at a 45 degree angle. The mirror then reflects the image upwards to a five sided prism and the image can be viewed through the view finder. When the shutter is released the mirror flips up, allowing the film to be exposed. After a roll of film is shot, the film gets developed and then images can be printed.

After breaking down how an SLR works you can now understand what single lens reflex means. Single lens refers to the single lens in the camera that is used for both the viewfinder and the picture taking. The term reflex refers to the reflex of the mirror flipping up allowing the film to be exposed. Now you can go impress your friends with your new knowledge!

A typical old school SLR camera


A DSLR camera is based off of this same idea as an SLR. The only difference between the two is that the film was replaced by a light sensitive digital sensor. In 1975 the Eastman Kodak company invented the digital sensor, revolutionizing photography. This monumental invention pushed photography into the modern age and people now use this technology every day. When the first digital cameras came out they produced very low resolution images and were very expensive. Over the years production cost of the digital sensor lowered substantially resulting in more affordable DSLR’s.

Canon DSLR camera

The “D” in DSLR

The invention of the digital sensor is probably the biggest photographic invention since film. It allows photographers to capture and view an image in a matter of seconds. No longer do you have to wait to develop and print an image to see the result. But I don’t  know if a lot of photographers actually understand how a digital sensor works. This is understandable because it is very scientific and can get a little confusing, but I think its important to understand the basics. I am going to try to explain in the simplest way how a digital sensor works but If you want to learn more I highly recommend researching it because it is very fascinating.

Just like film is light sensitive, a cameras digital sensor is also light sensitive. Technically speaking most cameras use a CMOS sensor, this stands for complimentary metal oxide semiconductor. The sensor is constructed of lots and lots of mini photo sensors. When light photons bounce into the photo sensor it creates an electrical current. Depending on the brightness of the light the current will be lower or higher. This current is then essentially turned to pixels and the pixels are put together to create a color image. All this takes place in the blink of an eye and the result is an amazing image.

The sensor is the shiny square in the middle of this picture.

DSLR vs. Mirrorless

With newer technology came the mirrorless camera. There is no mirror in a mirrorless camera, thus giving it the ingenious name.  Light travels strait to the sensor and can be viewed on an LCD screen on the back of the camera. If you have ever used live mode on an DSLR this is essentially how a mirrorless camera works. Some mirrorless cameras have a viewfinder but they were just put in to give the feeling and comfort of a DSLR.

People usually move to mirrorless cameras because they are smaller and cheaper than DSLR’s. The argument can be made that mirrorless cameras have smaller sensors and poorer depth of field. This is thought to result in a lower quality image. People will argue all day about what they think is better but I think one day mirrorless will prevail once the technology catches up.

As you can see, mirrorless are much more compact than DSLR cameras.


SLR’s were invented as a more compact and efficient way to take photos. In 1975 Kodak piggy backed off of the original design and integrated digital sensors into those same SLR cameras. Digital sensors used light sensitive technology to turn electronic current into digital images. Whether you are brand new to photography or you have been doing it for years, its nice to know how the technology in your camera works. I think a lot of the times we take for granted the technologies we use everyday. By understanding the technologies in things we use everyday, it allows us to have a deeper appreciation and love for them.

I hope the next time you go out and use your DSLR you stop to think about all the crazy stuff that is going on inside that little black box. And then think about how light photons are being converted into a picture that can be hung up on your wall. Its no wonder when photography was first invented people thought that it was magic.

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