Is there a preferred Depth Of Field for portraiture?

whiskaz wrote in post #2213069
Telephoto will actually give the illusion that the background is closer to the subject... if that makes any sense. I need a picture to illustrate but.... take a picture of a flower with a house behind it with a wide angle lens... now pull out the telephoto, back up to get a similar FOV. The house will now appear to be closer to the flower, as if there's not as much distance between the 2.

Someone else will likely explain it in more "scientific" terms and provide helpful pics but... oh well

Hey Jeremy,

No I understand this perfectly. Now that I think about it I remember learning once that a trick in film making to fool the eye and make you think objects were closer than they really were was for them to shoot it with a long lens (if that is what it's called for motion picture lenses). It's probably one of the most common tricks or techniques in fim making.

Jon wrote in post #2212775
A factor, but not the only reason - subject perspective enters into it also.

JaGWiRE wrote in post #2212900
You mean the ability to isolate a subject from a clutter?

No - try this: frame someone for a portrait using the kit lens at 18 mm, then at 55, then put your 70-200 on and try it at 200. Notice how different the person looks. But the DoF in all 3 cases will be the same if you keep the subject size and aperture constant.

The nose is closer than the ears. If you use a wide-angle and are close to the subject, the nose is closer as a percent of the subject distance, compared to if you use a tele and get further away. So as the lens FL changes, the appearance of the face changes. It looks flatter with longer FL, and the features are more exaggerated with shorter FL.

Jon is right, the DOF is the same if the subject size (on the sensor) and the aperature are constant, but also consider that the degree of background blur is not the same as DOF at the subject. With a tele lens, you see less background, so it's seen a larger magnification, and looks more blurred; as compared to shot with a shorter FL.

Jon wrote in post #2215253
No - try this: frame someone for a portrait using the kit lens at 18 mm, then at 55, then put your 70-200 on and try it at 200. Notice how different the person looks. But the DoF in all 3 cases will be the same if you keep the subject size and aperture constant.

And by subject size I believe he means distance to subject =)

Different perspectives are the main reason we have different focal lengths (aside from convience sake). If changing distance to subject didn't change perspective, we'd just use a prime (nifty fifty! sharp and light!) and footzoom everywhere!

KevC wrote in post #2215458
And by subject size I believe he means distance to subject =)

Different perspectives are the main reason we have different focal lengths (aside from convience sake). If changing distance to subject didn't change perspective, we'd just use a prime (nifty fifty! sharp and light!) and footzoom everywhere!

No. If you keep the distance to subject constant the subject size as seen in the viewfinder will vary wildly across the range suggested. Keep the framing of the subject constant; subject should occupy about the same area of the frame with each lens, which means you'll be moving either you or the subject around.

Robert, the 50mm on your 30D is usually considered an ideal focal length for a good perspective when doing conventional waist-up portraits. Just find the right distance to fill the frame with your subject in a way that pleases you.

Perspective is controlled purely by the distance between the viewer and the subject and then a focal length is chosen to frame the subject appropriately. Being too close to the subject and using a shorter focal length contributes to the kind of non-flattering perspective that David described above. However, decades of experience in photo studios by thousands of photographers has told us that the camera-to-subject distance properly framed with an 80mm lens on a 35mm film camera (which provides the same field of view angle as the 50mm on the 30D) is the classic "ideal" for conventional portraits.

The background should be at least as far from the subject as the camera is in order to get the background somewhat out of focus. The generally suggested minimum distance from the subject to the background is about 6 feet.

Thanks again to everyone. I am slowly processing all of this and learning.

Jon wrote in post #2215474
No. If you keep the distance to subject constant the subject size as seen in the viewfinder will vary wildly across the range suggested. Keep the framing of the subject constant; subject should occupy about the same area of the frame with each lens, which means you'll be moving either you or the subject around.

I understand that... but I'm curious to see that DOF will remain constant if you change distance to subject.

I always though DOF was a function of distance to subject and aperture. Guess I was wrong. I know perspective is.... (well aperture has nothing to do with perspective).

Using the DOF calculator (link by Rhinotherunt) if one doubles the focal length, one decreases the DOF by a factor of 4. If one doubles the distance to the subject, the DOF increases by a factor of 4. So If I double the focal length and double the distance, (which would keep the framing about the same) the DOF should be the same.

KevC wrote in post #2215659
I understand that... but I'm curious to see that DOF will remain constant if you change distance to subject.

I always though DOF was a function of distance to subject and aperture. Guess I was wrong. I know perspective is.... (well aperture has nothing to do with perspective).

You're missing the third element - the reason that wide angle lenses have more DoF than teles - focal length is also a factor. (So is degree of enlargement, but in this particular case we're assuming the same camera and same final print size.)