Olympus-OM
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Re: [OM] Exposure compensation

Subject: Re: [OM] Exposure compensation
From: "C.H.Ling" <chling@xxxxxxxxxxxxxx>
Date: Sat, 23 May 1998 17:43:01 +0800
----------
> From: David Irisarri Vila <valicors@xxxxxxxxxx>
> To: Olympus Questions <olympus@xxxxxxxxxxxxxxx>
> Subject: [OM] Exposure compensation
> Date: Saturday, May 23, 1998 2:44 PM
> 
> How works this system? 

I assume you are talking about OM4 or OM4T.

>It´s like a spot metering in order to use it 
> with flash?

No! Spot function will be disabled with OM flashes mounted.

> When the  background  is  darker than the subject, what 
> happens with shutter control?
> 1. The flash intensity is reduced.
> 2. The flash intensity is always the same but  the  shutter is opened
> more time in order to capture the background, reducing the speed with
> danger of handshaking.

With camera in auto mode, shutter is always locked at 1/60s with OM
flashes. Camera will be operated at TTL flash mode (average meter the film
plan reflection). 

> 
> Would be a good idea to spot a value from the face of the subject 
> (ie. 1/8s) and to take another value from the deep background (ie. 1/2s)
> and after clear the values from the memory and put -2 exp values in
> the exposure compensation dial and fire with flash? 
> 

Put in your mind that the camera will measure the flash light reflected to
the sensor. The following factors will affect the light reflection:

1. The color of your object (for example the color of the clothes).
2. The color of the background.
3. The flash-object to flash-background distance ratio.
4. The ize of your object occupied the whole frame. 

So object to background light ratio at ambient light condition may not be
good enough for you to make the judgment on the compensation needed.

To be more accurate, you need a flash meter or use GN-distance calculation.
But when using GN-distance calculation please have a check on the actual
power of your flash. I have four OM flashes, they are all more than one
stop under the quoted values. (I measured with a Sekonic L-328, I have
double checked the flash meter with a gray
card+OM4T+100mm/f2+T32+Fujichrome 100D in TTL mode, it is within one stop
error).

It is not only happen on my OM flashes, a Nissin flash I owned in the pass
was also the same. I just wonder how they measure the GN values.

C.H.Ling
Hong Kong

> Please I would be very pleased if somebody could help me with this.
> 
> Best regards 
> 
> Dave
> 


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