Thierry
New member
Dick,
with all due respect, it is wrong to say that the FL is in any way responsible or a factor having an influence on the perspective.
When one takes 2 images from the VERY SAME (to be able to compare) view point with 2 different FL, the 2 resulting images are exactly identical concerning the perspective (the horizontal and vertical converging or diverging lines in the image). The reproduction scale is not the same, obviously, but the perspective yes. Just enlarge the 2 images to exactly the same scale and you will see that the lines do overlap exactly, thus the perspective is the same.
Best regards
Thierry
with all due respect, it is wrong to say that the FL is in any way responsible or a factor having an influence on the perspective.
When one takes 2 images from the VERY SAME (to be able to compare) view point with 2 different FL, the 2 resulting images are exactly identical concerning the perspective (the horizontal and vertical converging or diverging lines in the image). The reproduction scale is not the same, obviously, but the perspective yes. Just enlarge the 2 images to exactly the same scale and you will see that the lines do overlap exactly, thus the perspective is the same.
Best regards
Thierry
He means the subtended angle... if the lens axis is perpendicular to the middle of a 20m subject 10m away the subtended angle is 2(arctan (10/10) or 90 degrees.
The angle of view would be the same if the subject filled the format (viewfinder).
It is obvious, but, in this context, I think it needs pointing out: We use lenses of different focal lengths to allow us to get the reproduction ratios we want from different subject distances.... the view point (or subject distance) required to fill the format to the required degree, at the required scale, is dictated by the focal length and format (angle of view).
Focal length affects perspective by allowing us to vary the subject distance.
If you use a standard focal length lens (focal length equal to the diagonal of the format) or a wide-angle, and fill the format with a face, perspective makes the nose disproportionately large... if you use double the focal length at double the distance with the same format you do not get this effect.
If there are no obstructions in the way, if you want a tall tower in the middle distance to produce an image similar in size to that of a much smaller (part of a) building in the foreground you can achieve this by an appropriate combination of angle of view and viewpoint.... this can be used to good effect on buildings like churches, with a tower at the far end.
On a Calendar picture there was a tractor in the foreground, framed by a tree, and a small hill in the distance - by using a longer lens (from a greater distance) I made the hill look considerably higher, giving a better composition.