DSLR stands for Digital Single Lens Reflex. A quick Google or trip to Wikipedia will tell you that. But what does it mean, how do SLR cameras work and how are they different from other types of camera?
How SLR Cameras Work
Before we can compare the differences we must first understand how an SLR camera works. Let’s break it down.
The light we see when we look through the viewfinder on our SLR camera and the light that hits the image sensor when we make an exposure comes through a single lens. This might seem obvious until you consider that not all cameras work this way.
Some cameras have two lenses – one through which the exposure is made and another, either above or to one side, that enables you to see through and compose the photograph.
Essentially, since there is only a single lens, “what you see is what you get.”
Reflex gives us a clue as to how using the same lens to see through and also make the exposures is possible – reflection.
As you can see in the above image, there is a mirror placed at a 45 degree angle directly in the path of the light through the lens. This reflects the light upwards where it enters another reflective assembly above the mirror which corrects the image (remember, it’s been reflected!) and then directs it out of the viewfinder and into your eye.
Below is a crude drawing of the general path of the light through the camera when the mirror is in its normal position.
Think of it like a periscope in reverse – in principle it’s not really that different. But what happens when we want to make an exposure? Well, quite simply, the mirror moves out of the way when you press the shutter button and lets the light hit the sensor behind it.
Have you ever wondered why the viewfinder “blacks out” for a moment and the camera makes a “thunk” noise when you take a picture? The sound is that of the mirror being quickly moved out of the way and of course, because the mirror has moved, there is nothing to reflect the light from the single lens up into the viewfinder until it is put back into position again.
And that’s about all there is to it! Hopefully you now have a better understanding about how an SLR camera operates.
So what are the advantages of SLR cameras over other types of camera?
When SLR cameras first appeared one of the main advantages was that they were significantly less bulky than some of their twin-lens alternatives. Today, with the advent of small mirror-less cameras, this is no longer true and SLR cameras are among the largest a typical consumer would consider buying.
They are, however, still a popular choice and indeed the preferred choice among professionals. There are numerous reasons for this – but the main reason specifically related to the SLR design is that when you look through the viewfinder, what you see is very close to what you get in the exposure. This is a very important advantage for working photographers and for those who simply do not wish to deal with any potential margin for error.
What about the disadvantages of SLR cameras?
The most obvious disadvantage of SLR cameras is the bulk. Existing lens mounts and the physical space required to house the mirror and other optical components give the cameras a minimum practical size which is much larger than some of the alternatives. However it’s important to take this perceived disadvantage in context, as many photographers find the larger dimensions of the SLR cameras more comfortable when using longer and heavier lenses.
Another disadvantage is that the internal construction of SLR cameras is often more complicated, and therefore more expensive, to produce. This complexity and use of moving parts can sometimes raise issues of reliability and mechanical wear. However, again, I feel it is important to put this into context and point out that this doesn’t make an SLR camera inherently unreliable. It’s just a characteristic that is useful to be aware of.
Hopefully, that gives you a bit of an insight into how SLR cameras work. Knowing the basics will give you more confidence in your equipment and will stand you in good stead when it comes to more advanced topics, such as the difference between a 95% and a 100% viewfinder and when you should use the mirror lockup function on your camera.
Good foundation knowledge goes a long, long way!
Thanks for reading.