[photo-3d] Re: Flash for Realist

[Dylan the Hippy Wabbit <dylan.wabbit@xxxxxxxxxxxx>]

Linda Nygren wrote:

>Unfortunately most other small lightweight flashes (every one I have
>seen) will only give you automatic function options of, say, f4 and f2
>(with 100 asa film), even if they have about the same guide number/light
>output as the T20. You might find one that will give you f5.6 on auto.
>Flash manufacturers apparently assume (probably correctly) that most
>photographers prioritize distance of coverage over small apertures.

Ever look closely at how those auto flashes work?  The sensor cuts the
flash when a given amount of light is measured, obviously.  But the switch
for which aperture to match does nothing to the circuit.  It slides a mask
over the sensor, at least on every one I've seen.  The sensor now has half
the aperture, so it doesn't reach the trigger value until the flash has
emitted twice as much light.  For manual control the mask completely covers
the sensor, meaning it doesn't detect enough light any time before the
charge is all spent.

In principle you could adapt this to get whatever auto aperture you want. 
The techniques used by pinhole photographers could get you whatever size
mask you need, or perhaps a piece of neutral density filter would be
easier.

Never tried it myself mind, but maybe it will help.


Dave Spacey

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