Hi,

I'm quite new to flash photography and I would like to ask some questions
about that. I have Canon EOS 30 (Elan7e), Canon 28-135 IS 3.5/5.6 and Canon
Speedlite 550EX.


1. Flash's output power. As I understand all the documents I read before
E-TTL flash control the lighting of the object by it's output power and not
by Exposure Time or Aperture. That means the power of the light that comes
out of flash differs from photo to photo. I can't explain in any other way
why while the flash is on the Exposure time is always 1/60 sec and the
Aperture Value is 5.6. Is that correct?


2. How long the flash light is on? I found a nice photo which explains how
the flash works at FP
 http://www.camera.canon.com.my/photography/art/13lighting/big_images/i
mg/figfpfl ashchart.jpg ). It shows that the flash is on as long the shutter
is open. Is that true for normal flash use too? (When no FP is set) I quess
not, because if that would be true, the first or the second curtain wouldn't
work. Would someone explain (something like on the photo that I mentioned
earlier) how it really works please?


3. Having longer exposure times with flash. As I mentioned earlier while
using Program mode the Exposure time is always 1/60 sec and the Aperture
Value is 5.6. That means in most cases the object is always correctly
exposed, but the background is very dark or even black usually. The EOS
user's manual says you need to set longer exposure times to see some more
background. Having IS lense 1/15 sec should not be a problem.


But as soon I select TV and set Shutter speed to 1/15 sec the Aperture Value
starts blinking, because it can't open the aperture for more than 3.5. What
to do in this case? Should I just fire a photo having such settings? Is that
because the camera meters the ambient light only and it doesn't take care of
the flash so the Aperture Value starts blinking? Do you think while the
camera is set to TV the flash light is calculated separately and it fires
for the less time as the TV setting is (in this case 1/15 sec). If that
would be true I could switch to Manual and set Time to 1/15 sec, Aperture to
3.5 (even it is not correct at TV), which would meke me a better background,
but the flash will take care the main object would be correctly exposed.


Thank you very much for any information, hint or suggestion on how this
really works.


Peter


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