Chuck Norcutt wrote:
I have a 283 which I've only ever used on my OM-1. It is startling to
hear that it might fry my OM-2s. Can anyone verify Paul's statement?
Can anyone say why this is so?
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>Date: Tue, 6 Jul 1999 14:03:41 EDT
>From: Pauls0627@xxxxxxx
>Subject: Re: [OM] Flash questions
>In a message dated 7/6/99 1:57:29 PM Eastern Daylight Time,
>mickeytr@xxxxxxxxxxxx writes:
>> 1. Is it ok to use a Vivitar 283 with an OM-10?
>In general, yes. The original 283s had very high trigger voltages (around
>200v). They can fry the circuits in the later OMs (OM-2S, OM-3(Ti),
>OM-4(T(i))). I'm not sure specifically if this is a problem with the OM-10.
>My (old) 283 works great on my OM-1. I keep thinking I should get a new one
>to use with my OM-2S and OM-4. I think the new models trigger at about 6v.
>Paul Schings
>Coventry, Rhode Island USA >>
Chuck,
I don't have an answer for you but here are some comments based on
reviewing the body schematics.
There are two issues that may be mixed here (a) the trigger voltage
from the flash trigger capacitor which is switched by the camera to trigger
the flash and (b) the quench signal voltage ending the flash in ttl OTF auto
mode (from the camera).
(a) depends on the flash design. For third party flashes (non OM) I have seen
voltages as high as 500V (studio flash) but typically are less than 300V. The
trigger capacitor in the flash is charged and then connected across a small
transformer by the camera switch to generate a very high (5000V or so )
secondary voltage to trigger the flash tube. Since Olympus must accomodate
third party flashes at least to some degree the only question is what are the
switch ratings of the switch components in the various bodies.
(b) is a low voltage (3V) signal from the camera so as long as the load in
the flash is reasonable this should not cause damage to circuits.
I don't have specifications for the voltage ratings of the various cameras
but checking the schematics here are a few comments:
The OM 2 has a purely mechanical switch trigger circuit so it is very robust
against high voltage capacitor trigger transients.
The OM2N is also mechanical but includes an isolation diode improvement to
seperate the different connectors. In theory this diode could be damaged with
multiple flashes connected and a high enough applied voltage , but high
voltage diodes are easy to get so it is likely robust especially with only
one flash in use. Even if damaged at least one of the flash connectors should
continue working.
The OM2S uses an electronic silicon controlled rectifier switch and an FP
flash mechanical switch. The silicon controlled rectifier is capacitively
triggered by one of the main circuits which is itself triggered from a switch
tied to the first cutain.. The most common SCR's are rated at either 200V to
accomodate 110V RMS American supplies or 400V for European 230V supplies, so
it just depends on what Olympus chose. In theory even with an overvoltage the
SCR would just self trigger and the flash would go off on its own. So if the
switch in the 2S is easily damaged by the 283 this is somewhat surprising and
the SCR must be a very small geometry device.
Regards,
Tim Hughes
Hi100@xxxxxxx
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