View Full Version : Q's about 420EX speedlite on 300D

8th of July 2004 (Thu), 17:39
I'm curious why my 300D exposure meter never change eventhough I have my 420EX on. On manual mode eventhough I have a flash its like i still need to set my camera (f/stop and shutter speed) almost similar to not having a flash just to have a normal exposure.

8th of July 2004 (Thu), 17:57
Flash photography with EOS cameras is an art all to itself..


I'm not quite sure what you're doing, but be aware the flash behaves differently depending on what mode your using.. Auto, P, Av, Tv etc.. The power and timing of the flash can vary greatly...

The link I provided covers this in detail..

8th of July 2004 (Thu), 17:58
That's because E-TTL in the flash computes the amount of light needed based on calculations seperate from the camera. In manual mode, I just set my shutter speed to 1/100 (or whatever you want) and choose an aperture that I want (I don't pay attention to the meter reading) and let the flash determine the exposure needed. I get great indoor results that way. When using Av or Tv mode, the camera will attempt to meter for existing light and the flash will provide fill flash. Most of the complaints about the DRebel are when the individual uses P or Auto. For whatever reasons, the DRebel just doesn't perform well consistantly in P mode with flash. I normally use Manual anytime I am taking indoor flash shots and have been pleased overall.

9th of July 2004 (Fri), 06:12
The Flash exposure and the ambient light exposure are two separate events that happen to occur at the same time. You need to determine the proper exposure for the ambient light using P, M, Tv, Av, or Auto, and then for the flash using either ETTL or Manual. In P or Auto, the camera meters the ambient light but sets a floor on the shutter speed of 1/60 sec. That's why in low light you don't see the shutter speed change in P or Auto. In Tv, Av,and M, the camera meter reads the ambient light and you have to select the appropriate shutter speed or aperture or both. If you don't care about capturing ambient light you can set the Camera to M, set the shutter speed to the max sync speed, and use your aperture to adjust the depth of field. WHen you do this make sure that your aperture doesn't get too small(larger f#) and reduces the reach of the flash. The maximum distance the flash can travel is the Guide Number at F=1.0, Iso =100. Distance = GN/fstop at ISO 100. So a 550EX with the camera at F/8, at can travel 55m/8= 7meters at ISO 100. If you go to ISO 200 it is 7meters x 1.4 and at ISO 400 it is 7meters x 2.

9th of July 2004 (Fri), 11:09
... So a 550EX with the camera at F/8, at can travel 55m/8= 7meters at ISO 100. If you go to ISO 200 it is 7meters x 1.4 and at ISO 400 it is 7meters x 2.

The original poster was asking about the 420EX, so the numbers are slightly less. The Guide Number is 42 instead of 55, etc.

I always think about it this way: Before the flash sequence of events begins, the camera doesn't know anything about the light of the flash or how it is going to reflect and then meter. So, all the camera does is show you some bogus exposure solution based on no flash. However, you, the photographer know that you have a flash unit in a normal flash mode and ready to go. Then, when you push the shutter button all the way, the entire flash sequence starts: pre-flash, etc. It is only in the last split second before the main flash fires that the camera makes the last exposure computation and that is what is actually used.

Does anybody remember the short time duration between the pre-flash and the main flash? It is quick.

---Bob Gross---