Wow, that is an impressive page.  Nice work!   

David


Quoting Jinx <joecolquitt@clear.net.nz>:

> > The flash in my Canon Elph is probably a fairly typical example of a
> > modern flash. It flashes twice in quick succession, the first time is
> > for exposure and maybe focus. The second time it's for taking the
> > picture.
> 
> The Canon I have will do several flashes in very quick succession for
> focussing etc. I'm guessing it's at most 1/20th between them
>  
> > In old-fashioned flashes, the flash had an inverter charging a big
> > capacitor that had a Xenon flash tube across it, and a little SCR
> > that hit a second, smaller transformer to trigger the flash tube. The
> > big capacitor is drained pretty heavily and takes time to recharge,
> > it can't flash twice in a tenth of a second.
> 
> I believe it's current control using semis. The same way that extremely
> short flashes of a known length are made for high speed photography
> 
> What I think happens is - when the tube is triggered the xenon
> becomes pretty much a dead short across the reservoir cap and the
> discharge current is hundreds of A / cm^2 until the lower conduction
> threshold voltage is reached, at which time the flash stops. To make
> the flash shorter, you need to prematurely pinch off the energy supply
> to the tube before it's exhausted the reservoir cap (if there's only one)
> 
> I've been playing around with external flashes. Not difficult to build
> and control with a PIC
> 
> http://home.clear.net.nz/pages/joecolquitt/multi-flash.html
> 
> Despite cheap digital cameras, an extraordinary number of used
> disposables are available free from processors
> -- 
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
> 




-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist