The Basic Principles of an SLR

Every day, more than 95 million photos are uploaded to Instagram. Let that sink in for a moment. 

95 million. A day. 

Few art forms have become as widely accessible as photography. Most people now have in their pockets the ability to quickly take quick, high-definition, crystal-clear photos, and post them for all the world to see. 

Everyone is a photographer.

Even so, the photos you can take with your phone give you little control over many of the aspects of the photo you’re taking. The standout photos you see on Instagram, with interesting lighting or special focus? The ones that make you stop the mindless scrolling? Those are almost always taken with a camera, not a camera phone. So if you’re ready to move beyond the point-and-shoot world of smartphones, I’ll help you understand the basic principles of using an SLR camera. 

SLRs (named as such because of mirrors and prisms, I’ll let you do your own research there) are fully manual cameras, meaning you choose how to use depth of field, lighting, and focus. Ever seen a photo of a runner completely in focus, even while he sprints? Or a photo of star trails? SLR.

When it comes down to it, using an SLR camera is all about understanding light—how much you’re letting in, and for how long. With this in mind, there are three variables you have at your disposal to play with.

• Shutter speed

• Iso

• Aperture

We’ll start with the shutter speed. You know the sound your phone’s camera makes—the k-chhh? That sound is a nod to the SLR, the sound of a shutter opening and closing. The shutter is what lets light through to the film or sensor. The slower the shutter speed, the longer the shutter is open, the more light gets through. 

So where does the light go? Directly to the film or digital sensor (depending on your camera). And that’s where ISO comes in. ISO is the “film speed”. That’s the sensitivity of the film emulsion or sensor, or, how much light it takes to react. A low ISO, say, 100, needs more exposure to light to form a photo. A high iso, say 1200, needs far less. The tradeoff is “noise”. More sensitive film creates a grainier photo. 

Finally, we get to aperture. Aperture is the size of the hole in the lens of the camera. If the lens is like our eye, the aperture is like our pupil. Much like our eyes adjust—larger pupils in the dark to gather more light, smaller in the day to allow in less—aperture adjusts the amount of light the lens lets in. The numbers are funky, always designated f/(a number), like f/2.8 or f/10. The tricky part is, because the number is inverted, the smaller the number, the larger the aperture. 

The biggest reasons to play with aperture is for control over depth of field. High aperture, or small lens opening, allows in less light but this means a crisper image in foreground and background. This is great for nature shots and distance shots where you want to clearly see most things in the frame. 

Low aperture, or large lens opening, allows for those images you see where the focal point is crisp and everything around it is blurry. 

So, let’s run through some scenarios.

It’s sunny out. You want to snap a picture of a butterfly on a flower. What settings do you want on your camera? 

You want a fast shutter speed, low iso, and low aperture. Fast shutter speed makes sure you aren’t letting too much light in, low iso ensures the light you do let in doesn’t overexpose, and the low aperture focuses nice and crisp on the butterfly while leaving its surroundings blurred.

One thing to remember is, all three elements interplay together. When you adjust one thing, other things need to be changed. If you change to a slower shutter speed, you may need to drop the ISO even lower so as not to overexpose.

Now, another scenario. It’s dusk. You are taking a photo of a mountain range behind a vast forest. Go.

You want a slow shutter speed, medium iso, and high aperture. Ideally, you have a tripod, which gives you more wiggle room with shutter speed and iso since your camera will be immobile, but a slow shutter speed and medium iso would let enough light in without giving you a grainy photo, and the high aperture gives you a crisp photo throughout. 

There is plenty more to learn about photography—we have only just scratched the surface. But at this point, the best thing you can do is get out there and play around with these basic principles. So get your hands on a camera, and start shooting.