Technical Term for Picture distortion?

miurasv

miurasv

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Hi all. Please can you help. I'd like to know what the technical term is for when a certain object in a picture doesn't appear to line up with what it does in real life. I have a picture of a V12 cylinder engine and the engine mounting in the engine block (red circle below) should line up with the 1st cylinder from the right air intake for the fuel injection above (red circle above) as the mounting is directly underneath the 1st cylinder but looking at the picture, which is taken at an angle, it's been said that the engine mounting appears to line up with the 3rd or 4th air intake from the right (yellow circle above). If this is the case, please can somebody explain what is happening and what the technical term is for it. Thanks very much in advance. Please excuse quality of picture.
 

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Perspective?

It all looks ok to me and if at the time of taking the picture you could have held up a little picture frame and angled it as you'd angled the camera to shoot you would maybe have been able to see the relationships with reference to the sides of the frame... if you follow me.
 
Most lenses aim at producing a linear perspective projection, i.e. straight lines in the world remain straight lines in the image, as a pinhole "lens" would produce, or as you would see looking through a frame at the scene. Most have some slight distortion in that some straight lines will be very slightly curved, but nowhere near enough a distortion to produce the displacement you suspect. This is not a lens distortion problem. It's a distortion in your expectations.
 
chris malcolm said:
Most lenses aim at producing a linear perspective projection, i.e. straight lines in the world remain straight lines in the image, as a pinhole "lens" would produce, or as you would see looking through a frame at the scene. Most have some slight distortion in that some straight lines will be very slightly curved, but nowhere near enough a distortion to produce the displacement you suspect. This is not a lens distortion problem. It's a distortion in your expectations.
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Thanks for your replies.Much appreciated. Distortion in my expectations? Please could you clarify. To your eyes which air intake does the engine mounting line up with?
 
It's perspective; the effect comes from holding the camera at an angle and viewing obliquely. As far as I can tell, the photograph shows exactly what you saw.

Try a small experiment with a pair of glasses (I just checked using a pair of reading glasses). If you open up the frame to make a right angle with the lenses, then view it from the side and twist the spectacles round so that you're viewing them from an angle as well, you'll see that things no longer line up.
 
StephenM said:
It's perspective; the effect comes from holding the camera at an angle and viewing obliquely. As far as I can tell, the photograph shows exactly what you saw.

Try a small experiment with a pair of glasses (I just checked using a pair of reading glasses). If you open up the frame to make a right angle with the lenses, then view it from the side and twist the spectacles round so that you're viewing them from an angle as well, you'll see that things no longer line up.
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Thanks, Stephen. The exact position of the mounting is actually in a line in between the 1st and 2nd air intake ports, slightly to the left of the first air intake from the right. So to your eyes is the engine mounting in line with and under the 1st air intake port from the right or the 3rd/4th air intake port from the right?
 
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To me it looks like it is under the 2nd. Definitely not 3rd or 4th.
 
Ploddles said:
To me it looks like it is under the 2nd. Definitely not 3rd or 4th.
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Thank you. If members of the forum could let me know which air intake port the mounting bolt hole lines up with to your eyes, I would be extremely grateful. There is a reason I am asking the question which I will explain later.
 
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That's actually a tricky question, and it depends on what you mean. If you move the photo to the edge of your screen and use that as a vertical line, you'll find that the red circles are actually directly above each other.

On the other hand, because the line is angled, we (well, I) automatically correct and mentally shift the line to a horizontal before estimating what lies above what. If you do this in Photoshop, a 19 degree twist results in the block being horizontal and the yellow and red circles being in a vertical line.

It's just a variation on the effect of converging verticals. We look up and see a tall building; we correct without conscious effort (or realisation, most of the time) for the fact that the walls are converging; or, if we're looking at a facade obliquely, we don't see that one end of the rectangular building is shorter than the other.
 
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StephenM said:
That's actually a tricky question, and it depends on what you mean. If you move the photo to the edge of your screen and use that as a vertical line, you'll find that the red cirlces are actually directly above each other.

On the other hand, because the line is angled, we (well, I) automatically correct and mentally shift the line to a horizontal before estimating what lies above what. If you do this in Photoshop, a 19 degree twist results in the block being horizontal and the yellow and red circles being in a vertical line.

It's just a variation on the effect of converging verticals. We look up and see a tall building; we correct without conscious effort (or realisation, most of the time) for the fact that the walls are converging; or, if we're looking at a faqcade obliquely, we don't see that one end of the rectangular building is shorter than the other.
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Thanks again. Makes sense. Yes, I agree the red circles are above each other. I was being objective in my original post as it was actually somebody else, who it would suit very much if the mounting bolt lines up with the 3rd or 4th intake, that said it.
 
You could ask for it to be moved to OOF as its not s photographic issue. The image shows exactly what we would have seen if we'd stood in that spot.
 
Its a shame richard is no longer with us, i'm sure he'd make an 18 minuite video explaining what lines up to what :D
 
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