Wow, thanks for the in-depth report! Very helpful indeed.
----------------------------------------------------
John Hermanson www.zuiko.com
mail: omtech@xxxxxxxxx
Camtech, Olympus Sales & Service since 1977
21 South Lane, Huntington NY 11743-4714
631-424-2121 Turnaround 4-5 weeks
----------------------------------------------------
----- Original Message -----
From: "Hughes" <hi100@xxxxxxxxxxxxx>
To: "Olympus List" <olympus@xxxxxxxxxxxxxxx>;
<lhawkins@xxxxxxxxxxxxxxxxxxxxxxxxxx>
Sent: Wednesday, August 20, 2003 1:10 PM
Subject: [OM] T-series limit on number of flashes?
> Lee H. asked why there is a recommended limit of 9 for the number of
Tseries flashes that can be
> connected simultaneously?
>
> Having modified a number of 3rd party flashes for use with Oly gear, I am
fairly familiar with the
> T series ccts. The OM2N service manual has some of the best published data
on the interface. Here
> is my best guess:
>
> The short answer is the LED flash ready circuit probably constrains the
number of flashes, as it
> uses different current levels for the "flash connected" but **not ready**
vs "flash ready" state.
> When you attach many more than approx 9 flashes the flash ready current
level is reached from the
> sum of the flash connected signals before the flashes are ready.
> With more than 9 flashes the LED ready current total exceeds 20mA
(2.3mA*9) **when used on an OM2
> or OM2N**. Often small LEDs like these are only rated to handle 20mA
continuously, so this might
> shorten their life. In practise this is probably not a problem because the
relatively small total
> number of flash ready usage hrs. On some versions of OM2S's and newer
models the LED current comes
> from the camera battery so this last item is not an issue at all.
(Advantage to flash/battery
> eater OM2S!)
>
>
> Here is a more detailed discussion:
> The T32 and T20 ccts are very similar, although not identical in the
interface.
>
> 1) The main camera trigger cct has lots of margin to trigger multiple
flashes, as either a 400mA
> scr (OM2S-OM4) drives this pin or a mechanical switch (OM2N and earlier).
So you can **trigger**
> lots more than 9 flashes. With a TFlash connected the trigger switch must
pass current from a 33nF
> trigger cap charged to between 7 and 12V, a tiny load for the scr or mech
sw.
>
> 2) The quench trig circuit needs to sink an estimated 16-20uA (@ ~1.1V)
per Tflash, so a total of
> less than 180uA for 9 flashes. The limiting factor here actually depends
on a 10kOhm limit
> resistor in the case of the original OM2 body (originally designed for
Q310 flash). In the OM2N it
> depends on a buffer ic (ic103) which likely can drive more current but we
don't know for sure. If
> we use the OM2 as worst case (has lowest drive current), then it should be
able to drive more than
> 9 flashes since (3V-1.1V)/10k = 290uA > 180uA. So it should be able drive
maybe up to at least 5
> flashes more ( (290-180)/20=5 ). This is a rough estimate.
>
> 3)The LED flash ready cct/pin: Uses a 5V source with a 120k resistor
which drives ~30uA to the
> ready LED in the viewfinder. With 9 flashes connected this current totals
270uA. The spec for the
> threshold of flash ready from the OM2N service manual is 350uA. It is
probably not very
> accurately controlled but there needs to be some margin between these
levels. In theory if
> everything is as designed, you could connect another (350-270)/20= 4
flashes before you reached
> the threshold. The TFlashes also need to short out the LED briefly during
flash exposure. They do
> this with a transistor switch. It appears the drive current to the
transistor should allow it to
> drive quite a bit more than 20mA, so this is probably not the limiting
factor.
>
> If you did not care about flash ready LED being meaningful, then the
number of connectable flashes
> is limited by the drive current from the quench pin. You could do some
empirical testing to
> determine the drive available by loading the pin with a resistor and
checking waveforms on a
> scope. You could then make a rough estimate of the number of flashes like
I did above. This is
> quite likely different for each model of camera.
>
> Regards,
> Tim Hughes
> TimHughes@xxxxxxxx
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> < This message was delivered via the Olympus Mailing List >
> < For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
> < Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
>
>
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|