Re: Very fast Leica lenses for the very well heeled

Savageduck <savageduck@xxxxxxxxxx> wrote:
On 2008-09-17 10:05:24 -0700, Chris Malcolm <cam@xxxxxxxxxxxxxxxxx> said:

Bob <Crownfield@xxxxxxxxxxx> wrote:

5. What is the fastest camera lens that Carl Zeiss ever built?
The 50 mm Planar f/0.7 lens. It was created for NASA to take pictures
of the dark side of the moon.

They didn't know that there isn't really a dark side to the moon?
That's the name of a pop song. The moon rotates once a lunar month,
i.e. the dark side becomes the sunny side and vice versa once a
month. The moon no more has a dark side than does the earth.

Due to the synchronous rotational and orbital speed of the moon, the
same face is turned towards the Earth, relative to the Sun. The dark
side of the Moon is not visible from the Earth. Approximately 59% of
its surface can be seen fron Earth. The dark side is lit by the Sun,
but only visible when lit from a position outside the Lunar orbit and
could be photographed Sun lit from that position in space.

A lunar orbiter would move over the hidden side once every orbit. A
landing party could choose to land on the hidden side, to land on the
edge and drive over, etc..

My point is that many people confuse the dark side with the hidden
side. Like the earth the moon's dark side is dark during lunar night
and light during lunar day. There's no lighting difference between the
hidden side which can't be seen from the earth and the side we can
see. As on the earth the dark side of the moon is a temporary
night-day phenomenon, but the moon's day is a earthly month long.

Some celestial bodies do have a permanently, Mercury for example.

So there is no special side of the moon which needs a special light
lens to photograph. You do of course need a low light lens to
photograph the moon during the lunar night, just as you need one for
night photography on the earth. Note too that on the moon at night you
get more earthlight than you get moonlight on earth.

--
Chris Malcolm, IPAB, School of Informatics,
Informatics Forum, 10 Crichton Street, Edinburgh EH8 9AB


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