Why are telephoto lenses used to blur the background more in portraits?

Question

Isn't aperture the factor that affects the depth-of-field? (Wide apertures give narrower depth-of-field while narrower apertures give wider depth-of-field)

Telephoto lenses tend to have narrower apertures.

Wide/fast apertures are more common in normal lenses.

So, why do photographers say that telephoto lenses make it easier to blur the background more in portraits?

Answer 1

Aperture is just one of the issues, the lens focal length is the other factor. Longer focal lengths will give narrower depth of field at the same aperture than shorter focal length lens. This makes it possible to use moderate apertures on these lenses but still achieve a relatively narrow depth of field. This allows the photographer to isolate portrait subjects from the background more easily with a longer focal length lens.

There are other reasons for using moderate telephoto lenses for portraits. They give a more natural perspective of a persons features, whereas shorter focal length lens can emphasis the features closer to the camera.

Answer 2

Two reasons in particular. If the depth of field is shallow and focused on the person, then that's the only thing the viewer will be able to pay attention to. It's hard to really pay attention to a blurred out bush if that's the background. It brings attention sharply to the subject and hopefully keeps it there. This can be particularly noticed if the subject is leaning against a wall or something, and the closer and farther sections of wall lose focus. Shallow depth of field brings attention to the subject only. Also, it flattens things out. Wider angle lenses curve things, and make it look as if it deserves to be on the inside of a dome. A portait, however, is usually in a frame, nice and flat. Telephoto lenses smooth out distortion and proportions to make the person look more natural, and more pleasing to the eye. Longer lenses give a flatter, more appealing portrait.

Answer 3

depth of field is controlled by :

focal length of lens
aperture
the distance you are focusing

telephoto lenses start with little to no depth of field relative to wide angle which have a depth of field from here to tomorrow given the same distance and aperture combinations

Answer 4

There are two main reasons.why I use a telephoto lens (canon 70-200 f/2.8 IS) for portrait work:

1. Hold you hand infront of your computer screen so its almost touching the screen and focus on the hand, but note the focus of the screen. Now, while still focusing on your hand, move it towards your eyes, closer and closer. Still focusing on your hand. Have you noticed how out of focus the computer screen has become? Why? because the screen is now much further away from your hand and your eye (or lens) can only focus on one point at a time.

So from this we learn the two keys needed for nice background blur: 1 - the back ground needs to be far away from our eye's focus point. 2 - we need the subject to be close to our eye. With my lens set at 200mm it will mean I will have to be quite far away from my subject (unless i want to take a photo of the eyebrow hairs), but guess what else ill be far away from? The background! Because its a big lens I can zoom in to the subject as well, making it look closer than it really is. So im satisfying the two key points needed for a nice background blur: a far away background and a close subject.

2. No one likes it when you are taking a photo right in their face. A tele lens lets the model relax because your not so close to them. (essential at weddings)

Answer 5

Aperture is just one of the aspects that can control depth of field. Basically the longer the focal length the greater the compression of depth in an image. Here is an article that gives you visuals on what I mean by compression of depth http://en.wikipedia.org/wiki/Telephoto_lens
There are other factors of course which can control the depth of field in an image. For example the scheimpflug principle can be applied to certain camera designs, in particular view cameras, allowing you to achieve maximum depth of field with the aperture fully open. http://en.wikipedia.org/wiki/Scheimpflug

Answer 6

That's not why a telephoto lens is used in portraits. A long focal length lens is more flattering to the subject. An exaggerated example of this can be seen by previewing a portrait thru a wide angle lens. The fish-eye effect will make the subject grotesque.