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-   -   Focal Length and Perspective (https://www.worldphotographyforum.com/showthread.php?t=998)

Adey Baker 22-04-06 23:17
Quote:
Originally Posted by robski
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.

Try it and see...you're defying the laws of physics if you think you can move the size relationships around without moving your position

John 22-04-06 23:19
Don, re your post number 12.

I think you are talking about the compression of planes that you get with long lenses. This is known as ariel perspective. But perspectve as I was using the term relates to the size of objects relative to each other. Christine's pictures illustrate this admirably. Or have I misunderstood you. What I was trying to give was a mathematical knock down proof that the relative size of objects in a picture depends only on subject distance and not at all on focal length. That is why I looked at the ratio ha/hb.

John

Don Hoey 22-04-06 23:24
John,

My interpretation of the effect of changes in presective was as in Christine post.

May well be wrong. Brain getting a bit fried. :D

One thing I will say, you have livened up our evening. I will go through this again tomorrow with a clearer head and daylight.

Don

robski 22-04-06 23:27
The point is that if christine had walked up the drive with the 100mm lens and stood in the correct spot you would not be able to tell the difference between the 100mm and 170mm shots. The same applies to DOF.

John 22-04-06 23:33
DOF Don, now there's another story; but I haven't the nerve to start another thread.
John

Quote:
Originally Posted by robski
The point is that if christine had walked up the drive with the 100mm lens and stood in the correct spot you would not be able to tell the difference between the 100mm and 170mm shots. The same applies to DOF.

John 22-04-06 23:36
Quote:
Originally Posted by Don Hoey
John,

My interpretation of the effect of changes in presective was as in Christine post.

May well be wrong. Brain getting a bit fried. :D

One thing I will say, you have livened up our evening. I will go through this again tomorrow with a clearer head and daylight.

Don
Good idea Don then you will get everything in the right perspective!

Don Hoey 22-04-06 23:37
Quote:
Originally Posted by robski
The point is that if christine had walked up the drive with the 100mm lens and stood in the correct spot you would not be able to tell the difference between the 100mm and 170mm shots. The same applies to DOF.
Yes Rob, I understand and agree with that. From my angle it is knowing the correct, if there is such a thing, term to describe the effect as in Christines shots, if it is not perspective.

Don

John 22-04-06 23:46
Quote:
Originally Posted by 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. :confused:

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 :D
Don once you start moving closer or farther away you are changing perspective. It is not the change of focal length that is doing it, that is only to fit the image on the screen.

John

robski 23-04-06 00:02
Don

The effect in Christine shots is changing perspective. But stickly speaking it is due to changing the magnification factor which is a by-product of changing the focal lenght. I know this may sound pedantic but it becomes important when trying to understand the science. If this effect was purely a function of focal lenght then moving closer would never give the same view.

Adey Baker 23-04-06 07:08
Quote:
Originally Posted by robski
If this effect was purely a function of focal lenght then moving closer would never give the same view.
That's right - it's the moving closer (or farther away) that changes the perspective. Focal length won't - can't - alter the perspective.


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