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I'll recap the situation. I am holding a magnifying glass at arms length
from my eye, looking at a lamp that is 10 feet away. That is, the distance
from eye to magnifying glass is much larger than the focal length of the
magnifying glass, and the distance from lens to the lamp is much, much
larger than the focal length.
I wondered why I didn't see the real image of an upside down lamp just
hanging in space. Instead, it looks to me like I am looking through a window
to an upside down world.
Here's what I think you all were saying: That upside down image in the lens
is in fact a real image.
It is in fact hanging in space in front of the
lens, but only looks like it is _in_ the magnifying glass.
After first reading this, I found it hard to believe.
It doesn't look like
it is hanging in space, closer to me than the magnifying glass, but you all
seem pretty smart, maybe you all are right. How can I check out this out?
I put the screen in the spot where the
image of the lamp was in focus and then I slid it down to create a split
screen effect, seeing at the same time both the image projected on the wax
paper and the magnifying glass directly.
If I were right and the image I see in the magnifying glass is different
than the one projected onto a screen, then it ought to be a different size.
Not only were they the same size, but every edge continued off the paper
into the lens with nary a break. My eyes were able to focus on both
simultaneously, further adding credibility to the idea that the upside down
image that appears to be in the magnifying glass is in fact the real image
made by the magnifying glass.
Why, then, would my thumb block the image when I am looking through the
magnifying glass without the screen?
I think that a carefully drawn ray
diagram shows the answer.