[fwlug] Last night's talk

[John McKelvey]

Chris,

You are welcome.  I enjoyed giving the talk.

John

On Fri, Jun 20, 2008 at 2:19 PM, Christer Watson <christer.watson at gmail.com>
wrote:

> John,
>
> Thanks for a really interesting talk. I thought the whole hardware and
> software limitations were really interesting to hear about!
>
> Cheers,
>
> --Christer
>
> On Fri, Jun 20, 2008 at 11:10 AM, John McKelvey <jmmckel at gmail.com> wrote:
>
>> Thanks for so many being there, and all most all staying awake.. {:-)
>>
>> I forgot in the photography portion to bring up something I found
>> interesting when I read about it in the late 1970's.  I pointed out last
>> night that it took about 5 photons, presumably reflected through the lense
>> from the photo subject of interest,  to render a silver halide grain
>> developable ...
>>
>> Now think solid state devices and "gating."  Suppose it takes 5 volts to
>> cause a device to "go on."  If a constant bias voltage of 2.5 is always
>> there then it only takes an additional 2.5 volts to trigger the device.
>>
>> Now back to film: suppose that the film plane is flodded with 2.5 photons
>> just before exposure by small LED's in the camera.  Then it would only take
>> 2.5 photons of light through the lens to generate a developable grain.  This
>> would mean doubling the effective film speed without increasing the grain
>> (typically related to film speed.)  In the late 1970s  the idea was
>> successfully tested, and it succeeded.  Exposure requirements were reduced
>> by almost a factor of 3 if I recall correctly..  an increase of effective
>> "system speed" of 3, or 3*400 = 1200 effective speed for TRI-X.
>>
>> Cheers, and thanks for letting me talk.
>>
>> John
>>
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>
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