Optics/Camera lens question - foreground

[spidey07]

You've seen the effect in movies plenty of times. Sometimes to add impact, most often the obect is a person.

Forground or center of frame stays the same and in focus but it looks like the background moves closer and closer or farther and farther away.

And at the same time the foreground doesn't change.

So just what effect is this called and just how in the world can a lens do that???

 

[KingNothing]

Green screen maybe?

 

[ThePresence]

I think he means how the background moves in and out of focus, it gets blurry, then sharp or the other way around. It just depends on the camera's focus.

 

[spidey07]

Originally posted by: ThePresence
I think he means how the background moves in and out of focus, it gets blurry, then sharp or the other way around. It just depends on the camera's focus.

nah, background stays in focus but moves.

Almost like you are zooming in at 2-4x but the center of the frame doesn't change.

 

[Savij]

I'm not exactly an expert, but I think it might be done with depth of field (focus). This link explains how to do it with a digital camera: http://www.olympusamerica.com/cpg_section/lessons/default.asp?val=5&action=29

On the other hand, I probably have no idea what i'm talking about and should be ignored.

 

[spidey07]

Originally posted by: Savij
I'm not exactly an expert, but I think it might be done with depth of field (focus). This link explains how to do it with a digital camera: http://www.olympusamerica.com/cpg_section/lessons/default.asp?val=5&action=29

On the other hand, I probably have no idea what i'm talking about and should be ignored.

Its similar, but doesn't have anything to do with focus....

Its like the background is zoomed in 2-4x.

We've all seen it in movies.

 

[Compudork]

If it is the effect I am thinking of, you can do two things:

Dolly in the camera while zooming out, or dolly out the camera while zooming in. This maintains the same basic field on the subject while causing a distortion the in surroundings. You manipulate the image optically with zoom, while counteracting that with physcially moving the camera. It's definately not easy, and takes a whole lot of practice to get right - but when you do it certainly looks nice! Good Luck!

 

[Legendary]

Camera backwards, zoom in, or vice versa - I forgot which one.

 

[spidey07]

Originally posted by: Compudork
If it is the effect I am thinking of, you can do two things:

Dolly in the camera while zooming out, or dolly out the camera while zooming in. This maintains the same basic field on the subject while causing a distortion the in surroundings. You manipulate the image optically with zoom, while counteracting that with physcially moving the camera. It's definately not easy, and takes a whole lot of practice to get right - but when you do it certainly looks nice! Good Luck!

that sounds about right and describes what I'm talking about.

 

[SandInMyShoes]

I believe it might be on-the-fly aperture adjustment?

 

[spidey07]

Originally posted by: pacmanfan
I believe it might be on-the-fly aperture adjustment?

but would aperature adjustment give the "zoom the background in" effect I'm describing?

that would only affect depth of field, right?

Wish I knew more about video production/editing.

-edit-
And while we're at it...just how in the world does aperature relate to video??????? I don't get it. I get it totally for stills...but video?

 

[Amorphus]

Originally posted by: spidey07

Originally posted by: pacmanfan
I believe it might be on-the-fly aperture adjustment?

but would aperature adjustment give the "zoom the background in" effect I'm describing?

that would only affect depth of field, right?

Wish I knew more about video production/editing.

-edit-
And while we're at it...just how in the world does aperature relate to video??????? I don't get it. I get it totally for stills...but video?

Video is just lots of stills being taken one after another.

Aperture is like the pupil of your eye - the larger the hole, the more light goes in. A smaller number (e.g. f/2.8) denotes a larger aperture, and vice versa for large numbers (f/10 is a very small aperture).

Read that article savj posted for more explanation - that's the main thing about aperture - DOF.

 

[LordMorpheus]

The camera is zooming out as it is moved closer to the subject, or zooming in as it is pulled away from the subject.