How to choose a lens to get a shallow DOF effect? [duplicate]

Question

Possible Duplicates:
Can I get a shallow DOF using a kit lens?
Help with getting bokeh effect.

I'm an amateur photographer, just getting into photography. I read some things about lens but I don't really understand.

I would like to take photos like this:

but with my current setup, which is the standard lens that comes with the Canon Rebel t1i, can't focus on the model at a distance very well.

So, the model is in focus but the background is more in focus than I'd like.

What kind of lens should I get to achieve the effect in the image I linked above?

Answer 1

Reading the EXIF info in that image reveals it was shot using a Canon 5D with a 70-200mm f/2.8L lens at 182mm

The 5D is a full frame body which gives a wider field of view at the same focal length. It also gives a shallower depth of field than an APS-C body like your t1i when matching the field of view. So to replicate this photo as closely as possible on your camera with respect to field of view and depth of field you would need a 113mm f/1.8

As Canon don't make a 113mm lens, you'll be able to get pretty darn close with the 100mm f/2.0, which is a very nice lens, though may be beyond your budget. To get a similar look without spending as much you could get a 50 f/1.8. However you'll have to be a bit closer and wont get the same degree of background blur. You can get very nice portraits with background blur with the 50mm but if you want to be able to do full length shots like the one you posted you need a longer lens, like the 100mm.

Answer 2

Simple Advice for a Beginner

Thank you for your question. I like it because it is clear and simple with a definite goal. I'm going to give an answer which does not consider all the technical aspects in depth, but is some advice which I wish I had heard when I was starting out.

Get a 50mm f/1.8 lens.

f/1.8 is wider than most lenses will go, giving a nice shallow depth of field.
Certainly, for the price, the quality and DOF of this lens can't be beaten.

Of course, there are other lenses which would work nicely for this sort of image (e.g. the 70-200 which was used to capture the example, as @Matt Grum points out).

Learn the Basics

Kit alone will not help you in the long term.
I suggest that you find a good educational resource (browsing this site wouldn't be a bad start) and learn the basics of exposure, depth of field, composition and so on.

Feel free to post more questions here as you learn :)

Answer 3

Depth of field is a function of focusing distance, focal length, and aperture. For the shallowest depth of field:

• zoom your lens longer
• open your aperture wider (lower numbers)
• shorten up the distance from camera to subject as much as you can for your framing while maintaining long focal length

Buying longer lenses (50, 85, 100, 135, 200...) with wider apertures (f/4, f/2.8, f/1.8, f/1.4) will get you the ability to shoot shallower. As noted by others, a fast 50mm f/1.8 is a great place to start learning, and they're relatively inexpensive.

Another thing happening in the example photo - they shot with a longer lens, so the subject has a more distant and flatter look. Had the shot been made with a shorter lens (50mm), the camera would have been closer for the same framing, a wider background would be included, and you'd feel closer to her as the viewer.

Answer 4

Looking at the picture, I can't help wondering whether at least part of what we're seeing may not be a result of post-processing rather than just shallow depth of field. Blurring that comes from being out of focus is basically progressive -- i.e., the farther something is from the focus point, the more blurred it gets.

Looking at this picture, however, that doesn't seem to be the case. For example, if we look at the far left edge of the picture, we see that the details of the building are quite blurred even though the geometry suggests that it's not much farther away than the subject. Compare that to the building at the far end of the street. Based on the geometry, that building must be much farther away from the focus point -- but if anything, it appears less blurred than the buildings at the edge that are relatively close to the focus point.

Likewise, looking at the pavement (or whatever) near the models' feet, it looks like there's noticeably more depth of field to the left than the right, and the area that's sharp looks to me like it's quite curved -- right in front of her, it gets quite blurry just a few inches from her feet, but off to the left and right stays sharper much closer to the camera. By the left an right edges, it's reasonably sharp right down to the lower border. While some curvature of field is common, this goes far beyond what I'd expect from any lens, to the point that post-processing looks to me like nearly the only reasonable explanation.

It looks to me like the photographer decided the subject wasn't sufficiently isolated as it was originally shot, and he adding some blurring of some of the nearer parts without doing blurring of the farther parts to match.

Note that I'm not trying to condemn the original photograph or photographer -- I'm just trying to point out that if you really want to duplicate the look of this picture, it may well take more than just selecting the right lens/body combo to reduce the depth of field. Of course, picking a good model helps too (and helps keep all but the most dedicated nutcases like me from paying any attention to the blurring of the buildings in the background...)