We’ve all seen the animations showing “how focal length affects your subject“. Whenever one gets posted, the smart ones chime in with “It’s nothing to do with your focal length, it’s all about subject distance”. And, they’re right. The confusion really all comes down to equivalent framing of the subject. If you stay where you are and just change focal length, nothing happens to the distortion in your subject’s face. They just get smaller or larger in the frame.
But, if you want to keep your subject the same size regardless of lens used, you have to move. With a longer lens you go further away. With a shorter one, you have to get closer. To illustrate this, the folks at Fstoppers have put a video together showing how the two work in combination with each other. The correlation between changing focal length and subject distance.
Ok, so he does say at the beginning, “changing just the focal length”. But, he then follows it up by saying “we will be changing the camera position, relative to the subject” to keep the same framing. So, they’re not really changing just the focal length, they’re also changing the camera distance, too. And this is what causes the change in perspective and weird facial distortions.
There is a reason it’s worded this way, though. The video demonstrates how it applies to shooting interviews. And with a seated interview, you’re generally on a medium closeup shot. This means the composition and having the subject fill a certain amount of the frame is pretty much set in stone.
But it does demonstrate that it’s not the focal length that changes how your subject appears to the camera. It’s the distance to the camera.
It’s as true with stills photography as it is with video. A 24mm lense may make look your subject look funny when you’re up close and filling the frame with their face. But, that distortion goes away when you step back for an environmental portrait.
If you want to fill the frame with your subject’s head & shoulders, then yeah, you want a long lens. At least, you do if you want your subject to still like you afterwards. Because then you can be at a decent distance from your subject, removing those perspective distortions.
But, it’s not the longer lens that reduces the distortion. It’s backing up from your subject that does that. The focal length of the lens merely determines the field of view and lets you get that tight shot again.
Try it for yourself. Stand a set distance from your subject and shoot them with a bunch of different focal lengths. Then scale the images so your subject’s head is the same size in each. You’ll see virtually no difference between them. Or, shoot a bunch of images with a 24mm lens, backing up a little after each shot. Do the same thing, resize them so they all match in size, and you’ll see that difference in perspective.
It’s also why “zooming with your feet” is the most nonsensical phrase in photography.
[via FStoppers]
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