[rollei_list] Re: little rollei flash
- From: "Robert Meier" <robertmeier@xxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Wed, 14 Feb 2007 23:16:27 -0600
Thanks, Carlos. We are in agreement. Robert
Yes more or less Robert, the sensor captures the flash
light coming back from the subject and the unit cuts
the flash light when considers the exposure was enough
and then yes, you are right from this point of view,
however I meant the existing light is conditioning the
flash reflection on the subject, the existing light
has to do very much with the flash duration, I can see
it every time I use the Vivitar 283 for the automatic
modes, BTW the subject distance also has to do because
closer the subject shorter the flash duration and
vice-versa; both factors, existing light and subject
distance are complementaries within the automatic
range to produce the flash reflection on the subject
and then the flash duration.
The Vivitar has a way to test if the exposure will be
right before to release the camera shutter.
All the best
Carlos
--- Robert Meier <robertmeier@xxxxxxxxx> escribió:
Carlos, in other words, yes? That is, not the
existing light, but the
flash's light reflected back off the subject
determines the duration of the
flash? Robert
The automatic flash units with sensor have a
computer
that calculates the flash duration according the
sensor info, the sensor captures the subject
reflected
light, less light from the subject more flash
duration, more light reflected from the subject
shorter flash duration.
The simplest flash units with sensor works automatic
for one distances range only, f.e. the referred
Rollei
20 works automatic from 0.4m to 4m only and within
this distance the flash computer calculates the
flash
duration according the light from the subject
selecting between 1/2500 sec to 1/30000 for the
flash
duration; a complex flash like the Vivitar 283 works
automatic for four distances range: 0.6m to 3.4m;
0.6m
to 4.5m; 1.2m a 9 m and 1.5m to 13-1m, each
automatic
distance range requires to adjust a different f stop
in the camera.
The Vivitar 283 has 1/1000 sec flash duration for
the
manual mode, and 1/1000 to 1/30000 sec for the
automatic modes. The guide number for the manual
mode
using ISO 400 film is 72, and then (f.e.) if the
subject is 20 metres from the camera you need to
adjust the camera f stop at f 3.5 (72/20= 3.6).
All the best
Carlos
--- Robert Meier <robertmeier@xxxxxxxxx> escribió:
> >The flash
> >duration for the automatic mode can vary from
> 1/2500
> >sec to 1/30000 sec according to the existing
light.
>
> Carlos -- Did you mean, according to the distance
to
> the subject (and thus
> the light reflected back from the subject)?
>
>
> ---
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