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Copper Coast, Co. Waterford
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C&C welcome…also question: why does the horizon curve like this, rather than just being plain ‘not straight’..or am i seeing something thats just not straight!
Hi Asterix,
What you are seeing is pincushion distortion. This is quite a common characteristic of poorly corrected telephoto zooms at the end of their reach. It looks especially bad in this example due to the fact that your horizon is also skewed.
The good news is that it’s easy correct in photoshop. I normally do my distortion correction first then level.
Andy
Andy, I don’t know… I was reading someplace that with the recent lunar eclipse, the moon had a very strong magnetic pull on the earth, in the lead up to and after the lunar event. That it caused massive gravitational pull and has caused large sea swells, as well as a shift in lava deep beneath the earths crust, around the globe. It said that it may also cause “optical swell” resulting in distant objects looking bigger than the are. I believe surfers in the northern hemisphere loved it. :roll: But to be honest though, this particular image does look more like optical distortion like Andy said.
Brian,
I’ve heard some excuses in my time. It sometimes fun when people defend their barrel distorted horizons as the earths “true” curvature. I love that.
There is an interesting mathematical equation to calculate the earths visual curvature at head height. It’s tiny !!
Here’s another interesting fact.
– When viewing from a head height of 1.75m, the true sea horizon is at 4.7km. Not as far as I had thought.Andy
amcinroy wrote:
– When viewing from a head height of 1.75m, the true sea horizon is at 4.7km. Not as far as I had thought.
My father always said it was 3 miles, but I expect you could be right
According to the acceptable tolerances used by lens manufacturers,
The earth is (optically) flat anyway-j
Pete,
That seems to agree with your dad’s old tale. But I suppose it depends how tall he was.
Now this gets really interesting. I’m really sorry for hijacking this thread.
Suppose that there is a person on an island 6 miles away and looking back at you across the sea. And suppose that you had a powerful telescope. He would therefore appear as a tiny floating pair of eyes and head above the horizon. You wouldn’t be able to see his body and you wouldn’t be able to tell what he was saying, even if you could lip read ! All you could do would be to shout “nice hat” at the top of your voice !
Andy
Guys does this kinda distortion happen throughout the focal length and aperture range of the lens or does it tend to be more common around the limits of focal and aperture say f/22. Or is it caused by something entirely differant like filters….
Brian,
I don’t think it is affected by filters or aperture.
It is more a focal length thing. Wide zooms tend to suffer from barrel distortion when used at their wide end and long zooms tend to suffer from pincushion distortion when used on their long end.
Prime lenses are usually more effectively corrected for distortion. But they are rarely perfect, especially at wide angle.
Andy
PeteTheBloke wrote:
amcinroy wrote:
– When viewing from a head height of 1.75m, the true sea horizon is at 4.7km. Not as far as I had thought.
My father always said it was 3 miles, but I expect you could be right
I reckon my eyes are at about 1.69m, but I could always wear me old platforms
from the seventies… Might see 4 miles then… :?amcinroy wrote:
Pete,
That seems to agree with your dad’s old tale. But I suppose it depends how tall he was.
Now this gets really interesting. I’m really sorry for hijacking this thread.
Suppose that there is a person on an island 6 miles away and looking back at you across the sea. And suppose that you had a powerful telescope. He would therefore appear as a tiny floating pair of eyes and head above the horizon. You wouldn’t be able to see his body and you wouldn’t be able to tell what he was saying, even if you could lip read ! All you could do would be to shout “nice hat” at the top of your voice !
Andy
When I was at school we visited a coastguard station in Cornwall (Porthgwarra, I think). The chap told us he was 230 feet above sea level and could see 27 miles. If the QE2 sailed by at a distance of 54 miles he said he could see the mast top lights because they are 230 feet above sea level too. This was when I was 12, so if I’ve misremembered the exact figures, please forgive me.
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