Macro photophotography is one of the areas in which the size of the sensor makes a difference. This photo is of an Eastern Dwarf Tree Frog clinging to a glass window

Digital SLR cameras have a sensor, which is the thing that takes the place of the film. The size of that sensor makes a big difference to how the camera behaves.

Back in the days when everyone used film, people often talked about using 35mm film in their SLR cameras. Now, when people refer to a full-frame digital camera, they are talking about a camera with a sensor about the same size as a full frame of 35mm film.

APS-C

APS-C stands for Advanced Photo System type-C. Aren’t you glad you know that? Here’s what that means.

APS was a format of camera film that allowed a choice of three different formats. The ‘C’ added onto the end referred to what was called the ‘Classic’ option for using that type of film.

An APS-C sensor cuts off some of the edges of a scene, compared with a full-frame sensor

How all of this relates to digital

An APS-C sensor is smaller than a full-frame sensor. This means that the edges of the image recorded by a full frame camera are cut off (cropped) by the APS-C sensor. If you look at the picture at right, you’ll get a rough idea of how much cropping I’m talking about. You will notice that the full frame captures quite a lot more!

So, why doesn’t everyone use a full frame sensor then?

Full frame sensors are bigger than APS-C and that makes them more expensive to make. So that added cost is passed on when you are forced to buy a more expensive camera. And sometimes APS-C can have its own advantages depending on what kind of photography you like. I’ll talk about that in this article too. Before I go on, I will point out that full frame cameras work the same as APS-C cameras, but because they capture a wider expanse of image, we can end up with slightly different images, and I’m talking about more than just how much gets saved or cropped off the sides.

Also, because the sharpest part of a photo tends to be in the centre, the bits being thrown away will usually be the least sharp part of the image.

Increasing the background blurring allows the foreground subject to stand out more

Backgrounds

Imagine you’re taking a photo of a flower with an APS-C camera. You’re standing in fairly close because you want the flower to fill the whole photo. Now imagine there’s some grass in the background. The grass looks kind of, well, grassy and you want it blur away to make the flower stand out more. So you open up your aperture as much as you can. That helps push the grass further out of focus. You take your shot. The grass is a little bit blurred, which is nice.

Now, you swap over to a full frame camera and you look through the viewfinder. Same lens. Same aperture. But, whoa! That flower no longer fills the frame. Now you’re seeing all the stuff around it which had been cropped by the APS-C camera. So what do you do? You move in closer to the flower.

Moving in closer does more than just bring your composition back to having the flower filling the frame again. Because you are standing physically closer to the flower now, you are focusing closer than you were before. And when you focus closer, one of the things that happens is that the depth of field gets smaller. That background grass is suddenly even more out of focus, meaning that the flower really stands out well now. So it’s the same subject, with the same lens, aperture and composition, but the full frame camera has resulted in a photo which is slightly different! In this case, you might prefer the full-frame camera.

Macro

So, you’re looking at that photo and that’s when you notice something. There’s a crab spider on the flower which you didn’t even see before because it was so well camouflaged. That changes things.

You have a macro lens and you want to fill the photo with that spider.

Now the APS-C camera might be more helpful because you won’t have to be as close to the spider to fill the frame. Which means you’re less likely to scare that critter away. And because depth of field is difficult to achieve in macro work, you might start appreciating the slight improvement in depth of field you get by being a bit more distant.

Having the sensor only capture the centre of a scene can sometimes work to your advantage

Distant objects

A bird suddenly lands on a plant about ten feet away. It’s a species which has never been seen before. Well okay, in my example at right it’s a Chestnut-breasted Mannikin which has been seen heaps of times, but now the bird fills the frame very nicely with the APS-C camera, but not so much on the full frame camera. Having an APS-C camera is like making your lens longer (more telephoto)!

Crop factor

Canon APS-C cameras like the 40D and 7D are often said to have a ‘crop factor’ of 1.6. Nikon APS-C cameras have a crop factor of 1.52. Sometimes people call that crop factor the multiplier factor and now I’ll explain why it’s such a big deal.

When you multiply the crop (multiplier) factor by the focal length of the lens, you suddenly see the difference in how a lens works on an APS-C camera compared with full frame.

For example, if you put a 100mm lens on a full frame it behaves like a 100mm lens. Well of course it does.

But if you put that same 100mm lens on an APS-C with a 1.6 multiplier factor it is still a 100mm lens but it behaves like a 160mm lens on a full-frame. So, by having an APS-C sensor, all your lenses act as though they are longer than they really are. Now, that might not sound like such a big deal with a 100mm lens but consider that a 400mm lens can behave like a gigantic (and expensive) 640mm lens when you stick it on an APS-C body. That can be brilliant for things like nature photography, where more telephoto can mean the difference between a good shot and a great shot. But not so good for wide angle. Because suddenly your beautiful wide-angle 20mm lens on the full frame behaves like a not-very-wide 32mm lens on the APS-C.

Specialised lenses

Some lenses are designed to only work on cropped sensors. So if you have a full-frame camera, you might find that you are unable to use some of the lenses available for APS-C cameras. Of course, if you’re buying a lens you should make sure at the camera store that the lens is suitable for your camera body. However, some people with APS-C cameras choose to only buy lenses that will work on both full-frame and APS-C bodies, because they might want to switch to full-frame later with the intention of taking all of their lenses with them. That’s a personal preference for those people of course and in my opinion it is neither right or wrong. For example, a photographer might decide that they plan to always stick with APS-C because it suits their preferences in photography. Alternatively, they might plan to eventually upgrade to full frame. Only you will know what is best for you.

Full frame cameras

PROS

• take full advantage of wide-angle lenses
• allows the photographer to move in closer to the subject and so reduce the depth of field
• the larger sensor has manufacturing advantages that can result in less noise in your images
• great for landscape photography and often preferred for street photography

CONS

• more expensive than APS-C
• more difficult to fill the frame with distant, easily-spooked subjects like birds

APS-C cameras

PROS

• less expensive
• telephoto lenses behave like something even more telephoto
• great for wildlife photos and macro

CONS

• wide angle lenses lose some of their wide-angle effect
• backgrounds can be slightly more in focus and therefore slightly more distracting

You might be seeing now how, just by changing the size of the sensor, it opens up all sorts of interesting implications for lenses and photography! And these differences are used to their maximum advantage by top photographers.

Beginners’ series on digital SLR photography

 

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