Focal Length and Perspective

[Don Hoey]

OK John I have saved your diagram so that I can view it while reading the explanation.

Maybe a couple of drinks in order to lubricate the ' little grey cells '.

Don

[Don Hoey]

Firstly let me say John education on the African plains was easier than this.

I am still trying to get to grips with the term ' Perspective ' in this discussion.

I have been compiling a reply in note pad that I have just read. Got totally confused and deleted it.

Being a simple soul I would look at subject A and decide how I wanted the background to impact on the final image. I may move closer with a wide angle to give depth to the background or move further away and use a telephoto to draw the background up. The relationship of other elements within either image would be quite different.

The question is then is that affecting perpective as I understand it. I would say YES.

Don

PS Phew

[Saphire]

Do you mean like this Don. I have been trying to get my head round this thread. It just so happens we were at Newports national sports centre today which has a very long drive. I was to lazy to put my 50mm lens on as we had been walking a while. The first shot was taken by Mario at a 100mm his shortest length and the second was taken by me on the same spot at 170mm my shortest length.
Added an extra photo I didn't realise Mario took one at 400mm

[Don Hoey]

Got it in one Christine. I did not even have to open the thumbnails to see the effect on the distant trees.

Well posted, thanks.

Don

[robski]

Christine

The logic is that if you walked up the drive with the 100mm until the people were the same size as in the shot at 170mm the trees in the backgound would also be the same size as in the 170mm shot. Therefore the perspective effect is due to the distance not the focal lenght.

[Adey Baker]

It's dead easy to check in about 2 seconds with a zoom lens on your camera - find two subjects that are at different distances but which appear the same size as one another. Now zoom your lens one way or the other and you'll see that they are still the same size as each other. QED

[Saphire]

AHHHHHH! Mario's pocket calculator has just exploded trying to work that one out.

[Don Hoey]

Originally Posted by Stephen

To my mind it is because the longer lens alters the whole dynamics of the image to the viewer. Although it may show the same area of the subject, the viewers eye sees the subject somewhat differently and generally in a more pleasing and flattering fashion. Not only this but the area behind the subject is different too. If you want to photograph a subject and crop out as much of the background as you can then I would use a long lens, whereas if I wanted to photograph the subject with a building behind I would bring the subject closer to the camera and use a wider lens. Simple photo technique that any photographer knows but the typical Japanese tourist doesn't seem to grasp

My opinion but Christines pictures show this effect very well, all be it at the telephoto end.

My question still stands. Is this not a case of using lenses to control perspective. If not how should this effect be described ?

Don

[robski]

Originally Posted by Adey Baker

It's dead easy to check in about 2 seconds with a zoom lens on your camera - find two subjects that are at different distances but which appear the same size as one another. Now zoom your lens one way or the other and you'll see that they are still the same size as each other. QED

Adey

You would have to move as well to keep the magnification factor the same. Because as you zoom and remain in the same spot you are changing the magnification factor. The factor which made the 2 objects the same size has now changed and therefore they will appear different in size.

The size of a near and distance object is due to the magnification factor. In the equation for magnification focal length plays no part in it. It is ratio of the lens to film/sensor distance to the lens to subject distance.

[Don Hoey]

Originally Posted by Adey Baker

It's dead easy to check in about 2 seconds with a zoom lens on your camera - find two subjects that are at different distances but which appear the same size as one another. Now zoom your lens one way or the other and you'll see that they are still the same size as each other. QED

Adey,

If I did this with my 28 to 105 lens then I would change magnification and the effect on the background would also alter. Wide angle to medium telephoto. Using a 24 -200mm would have an even more pronounced effect.

Its dark outside so I can't do an actual.

Don