Beginner What is that technique called?

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Scott
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#1
In videography where you have say someone's face in the foreground and say a door in the background down a corridor. Then something happens, the perspective of distance is zoomed in (or out) yet the person in the foreground remains in the same perspective.

What is this technique called?
Can it be done with my SLR?
Am I making sense?

Ta
 
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Caleb
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#2
Am I making sense?

Ta
No, well not to me. Reading through your post again are you trying to zoom in or out on the background as you've put both. If you are just trying to bring in more of the background just use a smaller aperture and larger depth of field.
 

MWHCVT

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#3
I think know what you mean, I suspect you mean this..

Dolly Zoom Effect:

http://www.youtube.com/VNO3BtNT9bY

Where the position of the camera changes to compensate for a change of focal length, so in theory this can be done with DSLR but to do it well you need to be able to move the camera smoothly, when doing this its done with a camera rig on a set of rails so the camera movement is smooth
 
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#4
I've heard it called 'crash zoom' I think, or 'dolly zoom' that describes it rather better, as popularised in MJ's Thriller video.

As Matthew says above, it involves moving the camera backwards/forwards (on a dolly) while simultaneously zooming the lens so the main foreground subject stays the same size and only the background changes. Easy in theory, not so easy in practise.
 
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#5
If your thinking of an effect like this (go to 50 secs in if you want to get to the first example):


Its called a 'Dolly Zoom', or 'Vertigo Zoom' or 'Hitchcock Zoom' (as he used it in so many of his films) amongst many other names: quite literally you move the camera forward/back (usually on a wheeled mount called a 'dolly') whilst simultaneously zooming in/out in the opposite direction at the same rate so to keep the same plane in focus. It can be done using any zoom lens and camera, but it is fairly hard to do, and much easier to pull off it you're using a powered type zoom like they use in the film industry so to get the zooming smooth (for a DSLR it may be easier to do with a push-pull type zoom as powered zooms are fairly rare). The video above gives the theory behind it and ways in which you can try to do it. There are quite a few other prominent/famous examples in this video:

 
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I've heard it called 'crash zoom' I think, or 'dolly zoom' that describes it rather better, as popularised in MJ's Thriller video.

As Matthew says above, it involves moving the camera backwards/forwards (on a dolly) while simultaneously zooming the lens so the main foreground subject stays the same size and only the background changes. Easy in theory, not so easy in practise.

A crash zoom and a dolly zoom are completely different things!

Nor was it popularised by Michael Jackson - it's known as a Hitchcock by cameramen.

The problem with doing it on a DSLR is that most DSLR lenses are not parfocal. A proper TV/Movie camera lens keeps the same focal distance throughout the zoom range - so you zoom in, focus, then zoom out to the correct framing and focus is maintained. They are very expensive lenses (a News camera lens would set you back £10k and that's the cheap end of the market). DSLR lenses aren't parfocal, so as you did the dolly zoom, the focus would change.
 
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#8
That's the bugger. Dolly zoom, and I can't do it on my little Nikon. Oh well, cheers guys - very enlightening. It's a great effect, I had psychedelic ambitions.
 
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#9
I'll bet you can do it in post-processing with pro-level software and enough resolution to take the cropping. You do the dolly bit during shooting, then do the zoom (essentially just frame-by-frame progessive cropping) in post.
 
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#10
I'll bet you can do it in post-processing with pro-level software and enough resolution to take the cropping. You do the dolly bit during shooting, then do the zoom (essentially just frame-by-frame progessive cropping) in post.
If only that worked, it would make things a lot easier.

When you crop you aren't changing the perspective so even though your subject will be getting bigger in the frame they will still seem far away from the objects behind them. When you zoom in you compress the foreground to the background but this doesn't happen when cropping; just like how a 50mm on a crop body will give a 75mm field of view, but still a 50mm perspective.

I've tried the dolly zoom many times throughout my film studies and only once by luck got something usable - I believe there is an equation for the "perfect" dolly zoom.

My favourite dolly zoom (zolly shot, as we normally refer to it at uni) is at 00:54 here:
 
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#11
Well you learn something new everyday :) I always wondered how they did that type of shot, now I know :)

Steve
 
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#12
If only that worked, it would make things a lot easier.

When you crop you aren't changing the perspective so even though your subject will be getting bigger in the frame they will still seem far away from the objects behind them. When you zoom in you compress the foreground to the background but this doesn't happen when cropping; just like how a 50mm on a crop body will give a 75mm field of view, but still a 50mm perspective.

I've tried the dolly zoom many times throughout my film studies and only once by luck got something usable - I believe there is an equation for the "perfect" dolly zoom.

My favourite dolly zoom (zolly shot, as we normally refer to it at uni) is at 00:54 here:
I might not have explained myself because I think we actually agree with each other. Croppping and increasing the focal length ("zooming in") are the same thing as far as the perspective is concerned (pixels not withstanding). The thing you can't simulate in post-processing is the camera movement. You have to do that physically by actually moving the camera. In a dolly-zoom the camera movement and focal length change cancel out as far as the subject is concerned (as you move closer you reduce focal length or vice versa) so only the background or foreground change size. All I'm suggesting is to simulate the focal length change in post - but you still have to do the dolly movement,

I can belive that there is a formula. I'd imagine that it is somthing like focallength/distance = constant
 
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#13
I might not have explained myself because I think we actually agree with each other. Croppping and increasing the focal length ("zooming in") are the same thing as far as the perspective is concerned (pixels not withstanding). The thing you can't simulate in post-processing is the camera movement. You have to do that physically by actually moving the camera. In a dolly-zoom the camera movement and focal length change cancel out as far as the subject is concerned (as you move closer you reduce focal length or vice versa) so only the background or foreground change size. All I'm suggesting is to simulate the focal length change in post - but you still have to do the dolly movement,

I can belive that there is a formula. I'd imagine that it is somthing like focallength/distance = constant
Ok, bear in mind its 1AM and I've had a beer and this is by no means scientific but hopefully it will demonstrate well enough :D

Both of these photos were taken from the same camera position, the first one was cropped and the second one was zoomed in.





As you can see, in the zoomed one the guitar appears much closer to the bottle than in the cropped image even though both were taken from the same camera position and have roughly the same subject size. Without the camera movement and focal length change you don't get the same dramatic change in perspective as seen with my beer.

Obviously I've done nothing with moving the camera and you will get very small changes in perspective as you move the camera back and forth but nowhere near as much as movement plus zoom.
 
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#14
Ok, bear in mind its 1AM and I've had a beer and this is by no means scientific but hopefully it will demonstrate well enough :D

Both of these photos were taken from the same camera position, the first one was cropped and the second one was zoomed in.





As you can see, in the zoomed one the guitar appears much closer to the bottle than in the cropped image even though both were taken from the same camera position and have roughly the same subject size. Without the camera movement and focal length change you don't get the same dramatic change in perspective as seen with my beer.

Obviously I've done nothing with moving the camera and you will get very small changes in perspective as you move the camera back and forth but nowhere near as much as movement plus zoom.
You have seriously weird zoom lens. From a fixed poition, size of objects won't change size relative to each other. Changin focal length simply alters the field of view.
 
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#15

DSC_7400
by winkyintheuk, on Flickr

This one shot at 80mm and cropped


DSC_7401
by winkyintheuk, on Flickr

This one shot at 200mm

The camera was on a tripod and didn't move between shots. You can see that the perspective is identical. Check the focal lengths on the Exif data. The objects are about 1.5m apart.
 
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#16

DSC_7400
by winkyintheuk, on Flickr

This one shot at 80mm and cropped


DSC_7401
by winkyintheuk, on Flickr

This one shot at 200mm

The camera was on a tripod and didn't move between shots. You can see that the perspective is identical. Check the focal lengths on the Exif data. The objects are about 1.5m apart.
That's very strange, I didn't have mine on a tripod so it's very possible that while fiddling around with the zoom I moved the camera!
 
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#17
WinkyP/Neil makes a good point, probably a useful tip for anyone wanting to try Dolly Zoom without a full film crew.

The essential bit is that the camera to subject distance has to change to create the perspective effect - that's the Dolly bit. At the same time, the lens needs to be zoomed to keep the main subject exactly the same size in the frame. This is not easy to do accurately on your own!

Neil's suggestion of adjusting the size of the main subject by cropping in post-processing is a handy trick for accurate framing. Maybe not for doing the whole zoom thing, but for tweaking a less than perfect zoom action.
 
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#19
Can it be done with my SLR?
Yes.. if your SLR has video recording.

Let's assume a 18-55 zoom lens.

Decide on closest point to subject, mark the floor, stand there and set lens to 18mm. Remember how big they are in the frame.

Zoom to 55mm and move back until the subject is the same size in the frame. Note the distance with a mark on the floor.

Move camera from furthest to closest points while zooming from 55 to 18mm smoothly.

You can buy a dolly that fits most tripods, even if you have to botch it a bit to secure it to it. Gaffa tape works wonders :)

Of course you also have to maintain focus as well as zoom. Have a go. You'll probably start to understand why when watching end credits there's the job title of "focus puller" :)
 
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#20
I can vaguely remember watching a TV programme a good few years ago about a chap who was working to develop a lens that would produce the sort of effect you talk about. I dont know if he succeeded or not.
If you want to see some pretty good Zoom effects watch Top Gear.

eddie
 
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#21
I can vaguely remember watching a TV programme a good few years ago about a chap who was working to develop a lens that would produce the sort of effect you talk about. I dont know if he succeeded or not.
If you want to see some pretty good Zoom effects watch Top Gear.

eddie
No lens alone can recreate a dolly zoom. The camera has to physically travel towards the subject.
 

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#22
Of course you also have to maintain focus as well as zoom. Have a go. You'll probably start to understand why when watching end credits there's the job title of "focus puller" :)
That's a very good point. I had sometimes wondered about that, and now I know. It's clearly a job that requires a lot of skill.
 
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