>>Here is how I do it with the same combo of OM-4 and T-20, T-32 *and* F-280
>>using TTL OTF mode:
>>1. Make sure the camera is in Auto mode with the ASA set for the film
>>speed you are using, and the EV compensation ring on the ASA dial is set to
>>ZERO.
>>2. Mount the flash to the camera but leave it *OFF*.
>>etc..
Sadly, although this is a great, clear description, IT DOESN"T WORK!!
Here's Why... (similar post as the last time the question came up... list
old-timers may experience deja-vu...)
In brief - you set the camera to expose the background correctly at around
1/60th. Then you turn on the flash and dial the compensation to underexpose.
Now what happens? Look in the viewfinder - as you dial in the -comp, then bar
graph goes up by the corresponding amount - the camera acheives the reduced
exposure by using a quicker shutter speed - NOT by turning the flash down. So
press the shutter, whether the flash is on or off, and the camera uses a faster
sutter speed than the sync and the flash doen't fire....
Or in more depth, think about how the OTF system operates...
In normal auto, with no flash, the ttl sensor looks at the film (or opening 1st
curtain) until it has seen enough light. If it sees enough before the 1st
curtain is fully across, it releases the 2nd curtain and you get a shutter
speed less than 1/60th. If it hasn't seen enough, it holds the shutter open
until either it has or 4 minutes is up, and then closes the second curtain.
Now turn the flash on... press the shutter, the first curtain opens and the ttl
sensor starts measuring the light just the same as before. If it sees enough
before that first curtain gets across (ie a resultant shutter speed of faster
than 1/60th)it releases the second curtain and the flash never gets to fire.
If it hasn't seen enough, it fires the flash. It then continues to measure the
light reflected from the film - remember it can't tell whether this is ambient
or flash light - and when it has seen enough, it quenches the flash and then
shuts the 2nd curtain. If it hasn't seen enough (ie the flash discharges
completely) it shuts the 2nd curtain anyway to maintain a shutter speed of
1/60th. NB You can prevent this by covering one of the flash contacts with
insulating tape - then (as with the original OM-2) if the flash isn't enough it
will hold the shutter open until enough ambient light reaches it (up to 4 mins
max).
So there is no way to alter the balance between the flash and ambient light in
auto - the 4ti is from a generation before auto fill-flash. So its back to the
tables, or ...
In auto, my KISS technique is to set the aperture so that the shutter speed bar
is just (1/3 -2/3rd)to the slow side of 1/60th. Without the flash turned on,
this would result in the camera exposing the scene at about 1/50th. Turn the
flash on, and by the time the 1st curtain is open, the sensor has already
almost seen enough light to satisfy it. It turns the flash on, which then only
has to 'top-up' the ambient exposure, resulting in a fast quench and little
flash released. I've no idea what ratio results (it would be affected by
distance) but it seems to work reasonably well. Perhaps someone with a
flashmeter could measure the output?
For important scenes, it's manual all the way. (No, I can't afford a 3ti
either...)
NB The Over-flash technique described by John DOES work, but, sadly,is much
less than use than fill.
Adam
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