NorthstaNder said:
Thankyou Gungir, at least it explains the reason for the perspective! Mind you, I guess I could have gone round the other side of the water by the Last Anchor and got a shot from there!
The perspective distortion when looking upwards at a building (aka keystoning) is a complete pain. Even the mark 1 eyeball is prone to it as the ancient Greeks knew a couple of thousand years ago.
Of course, when one looks up at a building one is aware that it is one's head that is tilted back and not the building and there are other visual cues which tell us this. Even so, there is a school of thought that the slight bulge at the midpoint of classical pillars (entasis) such as those of the Parthanon was in part an attempt to correct this optical illusion.
There are a number of means to reduce or eliminate this effect in a photograph. The simplest, as has already been pointed out is to move further away. This is only a partial solution and adds other problems of its own as a longer focal length will be required to fill the frame which has the effect of compressing perspective.
The effect can be countered at the taking stage by altering the geometry of the relationship between the lens and imaging plane. Large format rail cameras are the ideal solution as both the lensboard and the film carrier can both be moved completely independently of each other. 35mm SLR systems usually include at least one shift lens in the range which at a terrifying price allow you to correct keystoning in camera. I would be very surprised if both Canon and Nikon don't both still offer such lenses.
Once you have your latent image there are still options to correct keystoning. I can only speak of what I know which is the darkroom technique of pivoting the enlarger head (and negative carrier) in one direction and the lensboard the opposite way.
My ignorance of digital post-processing technique is impressive but I am determined to remedy this. I hope that you will forgive me but I have had a little fiddle. The result is somewhat disappointing as the keystoning was so severe that in correcting it your original composition has been butchered, but at least the Salthouse is no longer in danger of falling over! (Also my brain is rapidly turning to mush due to not having been able to get to sleep after a night shift at work so it could probably have been done slightly better)
