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DPChallenge Forums >> Hardware and Software >> 420EX Flash and Canon Rebel / XT
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06/29/2005 08:39:55 PM · #1
I have a problem using my 420EX flash with my Rebel XT.

The camera doesn't seem to automatically take the flash into account. Even if I use the FEC feature as follows:

1) I press down the shutter half way
2) I press the preflash button on the camera (still holding the shutter halfway down)
3) I press the rest of the way to take the shot

The exposure the camera calculates is the same with or without the flash. The exposure seems to be pretty good, because it seems the flash takes the camera setting into account. But then the only way I can take a good picture is to put the camera on manual, and then the meter function tells me it's about to be WAYYYY underexposed, even though the shot comes up perfect.

So what am I doing wrong? Shouldn't I be able to set the shutter speed to 125 and have it pick a decent F-stop for the exposure based on the fact that I have ambient light + flash? Or set the F-Stop and have it pick an appropriate shutter speed? Neither Av or Tv mode works like that. Only manual mode works, but still the meter reading is way off.

HELP!! Tell me how you use it please, and what I am doing wrong?
06/29/2005 10:29:06 PM · #2
Help!?!?!?!?!?!?!?
06/29/2005 10:36:24 PM · #3
I hope someone helps you because I am about to go buy the 420 for
my Rebel
06/29/2005 10:39:16 PM · #4
You are doing it all wrong...

First, what mode is all this stuff in? To make it easiest, put teh camera in Auto (green square) and the flash in ettl. Assuming you need to use the flash (an indoor room or other dark-ish area) it should work - aim, push shutter.

If it works, then we can move on to something more exotic...
as long as the flash is in ettl mode, and the camera is in a creative mode (P, A, T, M) it works like this:

Ignore FEC completely. It is an advanced feature and you can mess with it later if the pics you get are too dark or light. The asterisk button is still an exposre lock, and it will trigger a pre flash i believe - so you can set te exposure for something in the scene, recompose and focus and get the targetted area properly exposed.

Try P mode - the shutter will default to 1/60 sec. You then can adjust eh aperture. the flash will produce the necessary light, be it a little or a lot, to get a properly exposed image - unless you need more light than the flash can provide (f22 in a dark room for example with a subject 40 feet away...)

In A mode I beleive the shutter will default to 1/200 (or 1/250...) and you can adjust the aperture. works just as above.

You will probably NOT get a preflash. I have had the flash 'strobe' at times to get a focus point, but the way it works is the flash goes ON and stays that way until the camera decides it has the proper exposre and then it turns the flash off. the duration of the flash can be 1/1000 to 1/30,000 of a second. You may not see the flash fire.

In manual mode the meter will ALWAYS read too low. It reads ambient light ONLY, and does not factor in the flash. I beliieve the flash will work, again it will turn off when the proper amount of light has occurred.

I almost always use P mode and ettl. I control aperture and the electronics do the rest.

Message edited by author 2005-06-29 22:40:40.
06/29/2005 10:54:36 PM · #5
Neil, the procedure you're using was a hit-or-miss workaround for the original Rebel, which didn't have Flash Exposure compensation. The Rebel XT has true FEC, and you just prompted me to try it for the first time. "Flash Exp Comp" is the second item in your camera's second menu. Just change the value up or down to vary your flash strength (I just tried it with a 420ex, and it's works fine).
06/29/2005 11:03:56 PM · #6
Originally posted by scalvert:

Neil, the procedure you're using was a hit-or-miss workaround for the original Rebel, which didn't have Flash Exposure compensation. The Rebel XT has true FEC, and you just prompted me to try it for the first time. "Flash Exp Comp" is the second item in your camera's second menu. Just change the value up or down to vary your flash strength (I just tried it with a 420ex, and it's works fine).

The upgraded firmware 300D had FEC that actually worked.
06/29/2005 11:08:14 PM · #7
Originally posted by kyebosh:

The upgraded firmware 300D had FEC that actually worked.


You're right, but that was an unsupported firmware hack, not an upgrade. The 350D has FEC as an honest-to-goodness feature built right in.
06/29/2005 11:10:36 PM · #8
Sorry I wasn't clear before. I am not trying to use FEC (raise or lower the flash). I am trying to be able to control the parameters of the exposure while using flash.

So per your suggestion Chris, when I use P mode, it definitely shows that the camera is recognizing the flash is there, and the exposure is affected. Same for full auto (green).

But then how can I select the aperture or the shutter speed? P mode doesn't let me do that, does it? (Sorry if it does, but I don't see it, and I always use Av, Tv, or M mode.)

If I select the aperture, in Av mode, say F/8, the camera shoots for 1 to 3 second exposures, even though the flash fires.

If I select the speed, say 1/60 or so, you don't see the issue, but I suspect it's choosing the wrong aperture.

If I use manual, then I have to KNOW what to use, like an old manual flash! That's why I want to use Av or Tv.

Thanks...
06/29/2005 11:31:41 PM · #9
[Scalvert wanders back into the lab...]

OK, I see it now. The flash is recognized and appears to work properly (just turn the flash on and off and you can immediately see the difference in camera settings), but the numbers don't make sense. I just got 1/4 second without flash and 1/8 second with flash at a distance of 3 feet and f/2.8 in somewhat dim room lighting. If I put the camera on Auto, I get 1/60 second and f/2.8, but the results look the same. That's really weird.
06/29/2005 11:33:11 PM · #10
Originally posted by scalvert:

[Scalvert wanders back into the lab...]

OK, I see it now. The flash is recognized and appears to work properly (just turn the flash on and off and you can immediately see the difference in camera settings), but the numbers don't make sense. I just got 1/4 second without flash and 1/8 second with flash at a distance of 3 feet and f/2.8 in somewhat dim room lighting. If I put the camera on Auto, I get 1/60 second and f/2.8, but the results look the same. That's really weird.

the Flash compensates for everything with the power it outputs.
06/29/2005 11:38:29 PM · #11
Originally posted by kyebosh:

Originally posted by scalvert:

[Scalvert wanders back into the lab...]

OK, I see it now. The flash is recognized and appears to work properly (just turn the flash on and off and you can immediately see the difference in camera settings), but the numbers don't make sense. I just got 1/4 second without flash and 1/8 second with flash at a distance of 3 feet and f/2.8 in somewhat dim room lighting. If I put the camera on Auto, I get 1/60 second and f/2.8, but the results look the same. That's really weird.

the Flash compensates for everything with the power it outputs.


The flash seems to compensate nicely, but I want to be able to tell it aperture or shutter speed. If I select F/8, I would have expected the camera to recogize the flash is available, set the shutter speed to a good sync speed, say 1/60, and then, with the parameters now set to 1/60 at F/8, it should put out the right amount of light to complete the exposure.
06/29/2005 11:39:54 PM · #12
You need to set it manually, just keep your shutter at a reasonable speed and it should have plenty of power.
06/29/2005 11:45:05 PM · #13
Originally posted by kyebosh:

You need to set it manually, just keep your shutter at a reasonable speed and it should have plenty of power.


That makes sense, but it's unnerving to see the camera info flashing as if there's not enough light, when the flash yields plenty.
06/29/2005 11:51:07 PM · #14
Originally posted by scalvert:

Originally posted by kyebosh:

You need to set it manually, just keep your shutter at a reasonable speed and it should have plenty of power.


That makes sense, but it's unnerving to see the camera info flashing as if there's not enough light, when the flash yields plenty.


My sentiments exactly. It doesn't seem too friendly a user interface when you venture outside of automatic. I'd be curious to see if your G5 behaves differently. I'd try my G2 if it weren't brain dead. :)
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