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On 30 Jun, 18:56, "Peter T. Daniels" <gramma...@verizon.net> wrote:

> Then answer the question. How short could an exposure be during the
> Civil War?

Wet plate was the usual process by this time, it was in use from 1851
I think until about the 1880s. It was much faster than previous
processes, with exposures typically being a few seconds. I think you
might have got it down to a second in bright sunlight. Glass plates
for printing needed more exposure than Ambrotypes and Tintypes, which
were plates which were viewed directly by having a black backing which
made the image appear to be a positive.

Even with exposures this short it would have been difficult to keep
the camera still in a balloon basket. To make matters worse you'd
have to carry a darkroom tent with you, and coat, sensitise, expose,
develop fix and wash the plate within a few minutes before it dried.
It would then be varnshed, but this could have been done later.

Wet plate photography is actually seeing something of a revival at the
moment; there are almost certainly more people doing it today than at
any time in the last 100 years or so.

In article <>,
Chris H <> wrote:
>In message <>, Neil Ellwood
><> writes
>>On Sun, 29 Jun 2008 16:16:53 +0100, Chris H wrote:
>>> So any recce for a bombing air raid (from about 1920-1960) would have
>>> been by photography
>>>
>>> Before about 1920 it would be land forces again photography was used.
>>Aerial photography was used in the First World War.
>
>Yes but only on the battle field and was very primitive. Before WW1 it
>was very uncommon After WW! people knew how to do it. Then places
>started to get photographed from the air.

Aerial surveillance started with balloons (American Civil War) and pigeons
(WWI). But the problem is that few people think in 3-D. This is why camo
works. Other tricks of the trade exist (like IR) to defeat those measures.

The Smithsonian produced a fine book titled:
To Fool A Glass Eye

Stereo to resolve ambiguities is also an important key (most people
again have no concept why you want to do this). There's professions and
professional societies, but they are far from entirely military (the
ASP&RS in the USA).

>>> Also every man and his dog has photographed absolutely everything and
>>> put it on flicker or in stock libraries.
>>Neither myself or my dogs have put anything on flickr - no reason to.
>
>
>Me neither but you get the point. In 1930 you had to buy a guide book
>with a couple of pictures in and send a spy

Modern espionage changed radically at GC&CS to a game of signals from
linguists to mathematicians (this of course depressed the linguists).
This is both the strength of collection as well as a weakness.

>now you can probably find three pictures of any building in the world.
>And several dozen of any dam, railway bridge, telephone exchange, water
>treatment plant, etc.

As a generalization.

>>> The other possible reason is some idiot in the company that owns the
>>> bridges thinks they can make some money out of the photography rights.
>>That is a more likely reason, and that they believe they own the rights
>>to the air around it.
>
>More likely

Public works project. ;^)

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