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For anyone who is confused about the problem of focus: - how can you focus on the very close surface of the water and the distant horizon at the same time? Focusing a camera on a mirror can be confusing at first. If a mirror is two feet from the camera you'd naturally think you have to focus...

So the same should be true even if the plane of the film (sorry, sensor) is not perpendicular to the surface of the water. In that case you can use a physically larger lens angled up at the lower surface of the water.

For what it's worth: the Vieux Port Pavilion in Marseille. Sadly for our purposes it is not level nor completely flat.

The line at the midway point between the horizon in the (complete) inverted image and the horizon in the normal image is the astronomical horizon (?)

It's a clever idea, btw. Well down.

Yeah, you'd get two (at least) specular reflections with a normal mirror. You could use a sheet of reflective mylar glued onto an ordinary glass sheet. Edit: Or maybe a one-way mirror with an opaque backing. I'm not sure how they make them these days. They used to have a deliberately thin...

Hmmmm. And the mirror needs to be absolutely level, thus the water surface. Using a longer tube would help 3 problems: The partial image, internal reflections, and you'd be able to use a (physically) larger lens because you'd be able to focus on a more distant part of the water surface (I...

So, if there's a gap between the normal and inverted horizon lines, that equals the dip of the horizon? I'm trying to visualize why that would be so. The inverted image has reduced brightness, contrast and resolution. My first thought was that: -The inverted image is being produced by a...

Google Earth puts the sidewalk just in front of the green building at 10 feet above sea level. So the bottom 5.5 feet of the green building should be hidden.

[OP copied-in full-removed to help shorten reading time] There's so much confusion here I'm reluctant to even start but... So back to perspective; the human eye can roughly see around 30 miles with the best clear conditions. At that point the eye begins to have serious trouble discerning...

An important issue in FE belief is the concept of intuitive thought and analytical thought. I'm once again going to point to this review of Daniel Kahneman's book Thinking, Fast and Slow: http://www.nytimes.com/2011/11/27/books/review/thinking-fast-and-slow-by-daniel-kahneman-book-review.html...

This seems to be what the author of the video is assuming: Since half the earth is sunlit, and I can see exactly half the earth, and everything in the photo is sunlit, I should be able to see everything on the Earth that is in daylight. If I can't see it, it's not in daylight. But if you look...

Further into that article: Earlier I mentioned my fascination with round-earth trivia. Equally high on the fascination index is the wealth of lore and legend surrounding the old USC&GS (now NGS) and its efforts to establish reliable geodetic control nationwide. Most, if not all, geodetic...

It's important for everyone here to have a clear notion of the difference between plane surveying and geodetic surveying. Plane surveyors and geodetic surveyors have completely different education tracks and professions. The split between the two can be illustrated by this article from 2,000...

For what it's worth here's what it looked like when the lake was lower. It just looks like a retaining wall. Perhaps it was never meant to stand up to being topped for days on end and the original designers knew it would blow out. Perhaps it's better just to think of the whole area as the...

I'm just struggling to understand why this concrete structure is in danger of failing. Obviously they're concerned that it will fail at the bottom not at the top, which means something is eroding out from under it.

I'm completely naïve on this matter, but it seems this is metavolcanic rock we're talking about - specifically "greenschist-facies metavolcanic rocks of Jurassic age." It's a metamorphic rock, not an igneous rock like granite. How hard is this rock? How permeable? Is all that material we are...

The only thing I can predict is that there will be a lot of amateur placer gold miners on that stretch of the river below the dam this summer.

So it's like a concrete sidewalk, or maybe a curb is a better analogy, sitting on dirt. Erode the dirt away from under it, and it goes. So how far down is the bedrock? And why, oh why is the whole area below not covered in concrete - or, failing that, large boulders?

-It's unclear to me how the emergency spillway is constructed. It's not sitting on bedrock? -Is the power plant currently hooked up to the grid?