depth of focu question

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Drewcifer3000

Member
I know there's alot of shallow depth of focus threads in this forum, but hopefully this is a slightly new question.

I just got Barry's book/dvd and it was a great help. My only question about dof concerns zoom versus position of the camera. Barry says that a high zoom and getting as close to the subject as possible both contribute to shallow dof, but don't they contradict each other? Both make sense, but which one has a greater impace on the dof?
 
Well here's what we know...

Getting a longer (higher) zoom has an impact on the look of DOF because it forces a smaller area of the background to fill the background frame.

Getting the subject as close as possible to the camera means that you are focusing on an object in the field of view that is near the camera, thus increasing the distance between the focal point (object of focus) and the background. In effect, this is truly moving the background away from the focal plane.

As far as I can tell, in looks, both of these methods cancel themselves out sort of equally except for the fact that zooming in from a distance will crop down a lot of the background image. Really you should be doing both to a degree in order to get your desired elements in or out of the picture.

In the end, I think getting the object closer to the camera and farther away from the background is the technically true way of getting the background out of the field of focus. Zooming in doesn't move the background away from the field of focus, but rather achieves a similar result by forcing a smaller area to fill the screen and thus creates a blown up (or less sharp) background.

I don't think there is one real answer as to whether to typically move back and zoom in or to stay close to your subject. My advice would be to judge where you want the camera to be by decidedly cropping the background to the degree you want to crop it. Other than that, just try to get as far away from the background as possible if you want it blurry.
 
There is a problem with getting the talent too close to the camera. At full wide zoom there is some barrel distortion on the DVX. Even if you zoom in a little to where the barrel distortion is gone, there still is a distorted look to peoples faces when you are too close (http://cp.c-ij.com/english/photoshooting/techniques/camerafunction/camerafunction02.html). Those same headshots illustrate that zooming in gives you much more apparantly blurry backgrounds.

Neither of these methods actually effect depth of field, they are just moving the camera around to give the appearance. To really control depth of field, you need to use a low F-stop and light/ND accordingly. Then, just be smart about how you stage your scene, so there is distance between the talent and backgrounds. Use foreground objects as well. Use good cameras moves, light for depth, etc. Lots of techniques. Use them all well, and you'll get a great look.
 
Actually these do not contradict eachother. If zoom the lens all the way in and place your subject as close to the lens as you can, with the widest aperture you can, you will achieve the shallowest depth of field possible.
 
sellington said:
Actually these do not contradict eachother. If zoom the lens all the way in and place your subject as close to the lens as you can, with the widest aperture you can, you will achieve the shallowest depth of field possible.
Click to expand...

That's true.

There's just the matter of whether to back up the camera if you fill your frame before you zoom all the way in. That's where sometimes you kind of have to choose one over the other (decreasing zoom length or increasing distance between camera and subject) if you want to push things to the max.
 
Is this particularly effective with the XL1? I have problems with focus hunting, even in manual focus mode.

I have managed to get a semblance of a shallow DOF but there are problems with maintaining it when I am trying to move the camera with the subject while keeping the same distance between the lens and the subject.

Am quite new to video, so I'd really appreciate some help here. Apologies if it has been discussed already :)
 
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