[rollei_list] Re: Rollei Flash
- From: Don Williams <dwilli10@xxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Thu, 10 Jan 2008 22:37:49 -0600
Richard Knoppow wrote:
The difference isn't the caps so much as the circuits used.
Modern stobe units have some sort of impedance in the discharge
path through the lens which lengthens the duration of the
discharge. The old Kodatron lamps, which were I beleive the first
commercial strobe units, sounded like pistol shots when they went
off from the sudden mechanical change in the capacitors. These had
very short duration times, on the order of 1/50,000th second in
order to get motion stopping effect. Both duration time and
strobotron life is increased by lengthing out the duration time.
This also gets rid of the noise.
I measured my Vivitar flash for duration and found that at
maximum power it was on the order of 1/400th second, at minimum
power something like 1/20,000 second. Evidently the unit varies the
length of the flash to change its effective exposure.
I am not convinced about there being a radical difference in the
appearance of strobe vs: flashbulb pictures particularly if the
flash reflectors are approximately matched for size and location
relative to the camera. I have a means for testing this but won't
be able to get to it for a time.
I believe the difference in flash duration with output power setting
has used two different methods-
The early variable power units just integrated the light (photocell
sensor for those that measured the reflected light) until the desired
value was reached and then just dumped the capacitor with an electronic switch.
Very quickly new designs were produced which somehow opened the
circuit when the desired total output was reached.
In both versions the flash duration decreased as the power setting decreased.
My old 283 is of the newer design and the capacitor remains partially
charged after a "small" flash. I can run it at 2-3 flashes per
second (as a test) when flashing light colored objects close up. Fun
but not a practical thing except for close subjects and motor drive cameras.
Thyristor was the operative word, I think, for both versions.
DAW
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