TAKO. INTERNET SEIT 1996.
Olympus-OM

[OM] Re: Vintage E-1 matters and T20 flash

Subject: [OM] Re: Vintage E-1 matters and T20 flash
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
Date: Sun, 05 Feb 2006 21:08:41 -0500
I think your problem is that you're trying to get the camera to perform 
the flash's function.  Without TTL control of the T-20, the camera has 
nothing to do with the flash exposure.  It can't measure the flash 
exposure nor can it control the flash in any way except to initiate the 
firing of the flash.

The only form of automation that you have is the auto mode on the flash. 
   When the flash is in auto mode it will control its own output to make 
what it considers a proper exposure.  To make this work properly the 
camera should be in manual mode with a shutter speed less than or equal 
to the E-1's sync speed which is 1/180th second.  The longer this 
shutter speed the greater the addition of ambient light to the flash 
exposure.

This may be the cause of the overexposure you're seeing if you have the 
camera in auto mode.  In auto mode the camera is also trying to make a 
correct exposure but based on its measure of the ambient light as it has 
absolutely no knowlege that the flash exists let alone being able to 
measure or control it.  What you're probably seeing is a "correct" flash 
exposure controlled by the flash and a "correct" ambient exposure 
controlled by the camera for a grand total of twice as much light as 
required.

To regain your exposure composure place the camera in manual mode and 
use one of the two apertures as indicated by the auto mode dial on the 
T-20's calculator panel.  While you may think there are no electical 
connections there are.  One is a switch at the top left controlled by 
whether the calculator panel is inserted or not and the other is the 
slide switch at the bottom which informs the flash of the camera's 
aperture/ISO combination as set by you on the calculator panel.

After setting the camera's ISO on the flash you choose one of the two 
apertures based on the distance range you want to cover or other 
aperture selection criteria (such as DOF) assuming it fits with the 
available range of the flash at that ISO/aperture combination.

Remember that, with flash photography, there are always two exposures 
going on.  The first is the flash exposure which is extremely short and 
bright.  The second is the ambient exposure which you will allow or 
disallow according to the manual shutter speed you have selected.  If 
you choose a high shutter speed in a dark room there will essentially be 
no ambient exposure added to the flash exposure.  If you choose a long 
exposure, say 1/8 second, you may add a signficant amount of ambient 
light which may be useful for adding illumination to the background at 
distances the flash can't reach or can't reach with the same intensity 
as the foreground.  This dual exposure control is used in the reverse 
sense when doing fill flash.  In fill flash, the ambient exposure is the 
principal exposure and the flash exposure power is controlled such that 
it adds only a fraction of the ambient light level in order to brighten 
the shadow areas a bit.

Chuck Norcutt

Brian Swale wrote:

> 
> The current issue now is to get the E-1 to make well exposed images. So far 
> they are grossly over exposed. The shutter stays open far too long, f/22 at 
> 1.5 metres in A mode. Working on that now. P setting is worse.
> 
> Whether the T20 is set on manual or auto makes little change. (Don't see 
> how it could, as the panel seems to be merely a sliding-rule kind of 
> calculator. I can't see any electrical connection to the flash circuitry)
> 
> If the worst comes to the worst, I will control the issue by using Manual 
> mode, and judge the goodness of the exposure from the rear screen picture. 
> But that seems to be a clumsy solution. The camera should solve this 
> automatically.
> 
> Brian


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