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Originally Posted by pampanito
Would I be cheating if I use the UZO to locate targets at ranges of 15000 or so?
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Just to back up those figures above....
There are two things to consider. Geometry and aerial perspective.
The Geometry:
The distance to the sea's horizon is about three and a half times the square root of the height of the periscope, in meters. After this distance, the sea begins to hide the ship. This distance is what? About 5.5Km?
The height of the ship is say, 25m, then this can be seen over the sea from about 17.5 km.
To find out how far the ship can be seen, add the two together:
17.5 + 5.5 = 23km. After this the sea hides the ship completely.
Then you have to consider the effect of geometrical perspective on the part of the ship that is not hidden by the sea - ie the upper parts. Typically these will be very small in size. Think how a big ship that is just 7km away appears very small in the eyeglass. You can hardly see it. Of course zoom factors play a part here, but you'd have to have very good magnification to see the tops of masts at this distance. Smoke should easily be visible though.
Aerial Perspective
This is the tendancy for particles / vapour in the air to fade objects over distance. This varies greatly, but on extremely clear days mountains can be seen across the sea that are over 100km away. I read just now on a web site that in San Diego, it's sometimes possible to see San Clemente Island, which is 123Km from the coast. Also, in Malaga, Spain, I've often seen the Atlas Moutains in Africa, which must be a good 150km away. They say that 200KM is about the limit, though.
So we can say that if you have good optics (with powerful magnification), and it's a very clear day, then you should be able to pick the upper parts of a ship up to 20KM away - if you knew where to look!