On Perspective Control....

[Barney]

Perspective control and the size of background objects ?

I understand the principle that with a wide angle lens background objects appear smaller and that with a telephoto lens background objects appear larger.

What I have been wondering is if the relative distance from the subject that you need/want a factor of the apparent enlargement, or is it purely determined by the length of the lens ? Are there other factors at play here?

 

[woof woof]

Perspective is down to the camera to subject distance but obviously the length of the lens affects where you stand as follows...

Suppose I want a half body shot of Mrs WW and I have two lenses, a 20mm and a 200mm. With the 20mm I'll be stood right in front of her for the half body shot, she'll be BIG in the frame and the background will be small in the frame. With the 200mm lens I'll be much further away even though it's just the same half body shot and the background will look relatively large in the frame.

This is the "flattening effect" that some people describe but it's not down to the lens as such it's down to the distance you stand at to take the picture. If you stood at 200mm distance and took the shot with the 20mm you could crop the 20mm shot to get the same framing as the 200mm and it'd look just like the 200mm shot... assuming you had enough mp's to crop that much.

 

[Petrochemist]

'Perspective control' is the term Nikon uses for its tilt/shift lenses. Such lenses are typically expensive because of the need for a much larger image circle, complicated linkages & relatively low demand.
Shifting the the lens upwards from the centre of the sensor allows the camera to be kept parallel to a tall building while still getting the top of the building in frame or to take a picture of a mirror straight on without the photographers reflection showing...
Using a normal lens the photographer usually points the camera up at an angle which makes the top of the building look smaller than the base.

For those who don't want to play which such magic tricks, perspective is down to the distance from the camera just as @woof woof describes. Though lenses such as fisheyes can add further distortions which will sometimes change the apparent perspective further.

If you want to control the perspective in a normal shot you need to adjust both subject & background distances & then decide on a suitable focal length to get the subject the size you want. These shots use the same rock, but varying distances to my son, false perspective can take quite a bit of aligning, as one hand slightly out of place will ruin the effect.

Model closer to the camera
sml P1150595 bw by Mike Kanssen, on Flickr

Model back with the rock
sml P1150590c by Mike Kanssen, on Flickr

Please ignore the odd colours - thats down to something else I playing with at the same time

 

[StephenM]

It's in my book with photographs illustrating the principle.