External Flash Concept?

[tzjiang]

Hi DPS Members,
I need help on understanding help how external flash setting works. I'm not sure if people called these a flash concept.
I couldn't find a good article that explain it.

I did several experiments with Olympus Evolt E-510 (with max flash sync 1/180s) and Olympus FL-36. (I set it to TTL Auto)
The object is a table lamp(light on) in the middle of the room and there is wall about 5 feet behind from the lamp.


Here are the questions:
A. What is the difference between the first shot taken with (EC +2 and Flash EC -1) and the second shot with (EC +1 only and FEC 0)?
I didn't notice any difference in the results.It seems they yield to the same exposure. Is there any difference?

B. Please see the experiment tables below. I focus on the bright light.

In case you can't see the image table:
No Mode ISO A S FlashType EC FEC EC_on_EXIF Result
1 AP 800 5.6 1/640 No Flash 0 0 0 The wall is dark
2 AP 800 5.6 1/180(blinking) Fill Flash 0 0 0 The wall start show up
3 AP 800 5.6 1/180(blinking) Fill Flash 1 0 1 The wall brighter than second one
4 AP 800 5.6 1/180(blinking) Fill Flash 2 0 2 The wall brighter than third one
5 AP 800 5.6 1/180(blinking) Fill Flash 3 0 2 ?
6 AP 800 5.6 1/180(blinking) Fill Flash 4 0 2 ?
7 AP 800 5.6 1/180(blinking) Fill Flash 5 0 2 ?



I figured out the shutter speed blinking on 1/180 is because
the exposure value is greater than 1/180 while the flash max sync speed reached the max 1/180.
but why the EC on EXIF data is limited to 2 for the 5,6 and 7 tests although I increase EC?

C. Please see another experiment table below. Still focus on the bright light

No Mode ISO A S FlashType
1 AP 100 5.6 1/80 No Flash
2 AP 100 5.6 1/180 Fill Flash
3 AP 100 8.0 1/180 Fill Flash

Why the third result has the same shutter speed with the second one?
Isn't it supposed to be slower than the second one since I changed the aperture to 8.0?

D. What's the difference if you shoot using External Flash (TTL Auto) with different program mode?
I saw the article on DPS below but the result is not the same. Did I miss something?
An Introduction to External Flash Units


E. It's related to D question, how to make the wall behind completely dark (only the light bright)
or
everything bright (the lamp and the wall) when shooting with external flash?
How to achieve both results? Do we have to play with shutter speed and aperture? or 1st and 2nd curtains flash setting?

F. Some articles suggest to avoid blur, try to shoot with shutter speed above 1/60s.
Is the number still true if you shoot with flash?


Your answers is greatly appreciated.

Willy

Note:
AP: Aperture Priority
EC: Exposure compensation
FEC: Flash Exposure Compensation
EC_on_EXIF: Get EC number from EXIF.

[Cypher]

Hi there,

While I am far from educated enough to answer this I can share with you a great site for external lighting: Strobist best of luck !

[OsmosisStudios]

Flash exposure comp and camera exposure comp varies from brand to brand. You might be better off discussing this on an Olympus-dedicated forum (like that on DPReview)