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Re: [OM] Re: Flashmatic -was: Oly digest V2 #3283

Subject: Re: [OM] Re: Flashmatic -was: Oly digest V2 #3283
From: Jim Brokaw <jbrokaw@xxxxxxxxxxx>
Date: Mon, 08 Apr 2002 21:21:51 -0700
on 4/8/02 2:32 PM, ClassicVW@xxxxxxx at ClassicVW@xxxxxxx wrote:

> I've found that showing this formula is easy for a beginner to grasp:
> 
> flash's guide number
> Aperture- (F setting number)  =  ------------------------------
> flash to subject distance
> 
> The guide number for a T20 flash when you're using  100 speed film is the
> number "20", which refers to 20 meters. Divide the flash to subject distance
> (this distance as expressed in meters) into the "20" (guide number).
> So, for a subject 2 meters away, divide the "2" into the "20" and you get
> "10". Set your lens to a aperture ("F" number) of  F /11 (closest number to
> "10")
> 
> If you'd rather use "feet" as a measurement unit, you must use your flash's
> guide number in "feet" also. I think the T20's guide number in feet is 66. So
> divide your roughly 6 feet distance into the guide number of 66, and you get
> "11" for your answer. Set your lens to F/11
> 
> Always remember to set your flash to the film speed you're using. And you
> must convert your flash's guide number when you change your film speed. ( The
> guide number of 20 [in meters] is only used for 100 speed film).
> 
> George S.
> 

I recently bought a 35-SP which has "guide-number flash" settings on the
lens. I wanted to see how this works, so I set the lens for a guide number
(~60 in feet) and then opened the back of the camera. As you move the focus
lever from infinity to closer, the lens aperture closes down, which you can
see from the open camera back. Pretty cool, and allows use of non-automatic
flash with this camera. I think several of the old Olympus leaf-shutter
rangefinders had such a system.

Some things I have read suggest that this is a more accurate flash system
than the flash auto-sensor, as it won't be fooled by a light subject and
dark background and overexpose the subject trying to make the background
lighter when you focus on the subject. That can even happen using TTL
flash... I'll have to try it out and see.
-- 

Jim Brokaw
OM-1's, -2's, -4's, (no -3's yet) and no OM-oney... 


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