View Full Version : 420ex exposure problems

29th of June 2001 (Fri), 21:54
Does anyone else have problems with the 420ex over-exposing shots. I've noticed the following scenarios.

1) If the subject is backlit. With both spot-focusing, and normal, it tends to overexpose the subject.

2) If you are outdoors, and are trying to use the 420ex as a fill flash, (because the subject is in the shade), it fills okay, but for some reason, the speed is set to something ridiculously low like 1/60th of a second. With a flash, I should be up around 1/200th. As a consequence I get motion blur.

3) Cases where in P mode it will fire at full strength when it shouldn't. If I put it in auto mode, it does the right thing, and then back to P mode, and it seems to work again.

Generally I am quite happy with my 420ex/g1 combo, but I can't seem to figure out the rules to work around these types of problems. I've considered using Tv mode to deal with #2, but feel that I shouldn't have to. When it gets really bad, I use exposure and flash correction (-.5 to -1), and it helps...But still Why can't it meter the output of the flash correctly!!! That is what it is supposed to do.


5th of July 2001 (Thu), 09:50
Hi Mike,

I notice that you are not being slammed with answers to your problem. I posted a similar problem several weeks ago and received one response. Either it is just you and I having this problem, no one else shoots this way, or there is no solution.

I do model photography and like to shoot backlit. This is a real problem. One solution that was offered to me by the camera store was to use spot metering, but it appears that you have tried that. The G1 will not do fill in the sun (with the sun behind the camera). I like the convenience of the digital, but these problems are really taking the pleasure out of the camera.

The camera does appear to be heavily weighted toward the bright background in back lit, and does not perform fill flash (with the sun behind the camera) at all.

I am anxious to hear if anyone responds to your (and my) problem.


Eric F.
5th of July 2001 (Thu), 10:17
Hi Mike and Jim,

I do not have a answer for your problem. But do not stop asking it. I have a G1 and 420, but really do not have enough experience with the combo to know what it will and will not do.

We all are learning at a fast pace, but since the camera is still less than a year old, there does not seem to be any expert in all areas. The nice thing about this forum is the quality of questions inspire someone to try and figure out the answer. For some of the more tough questions only Canon has the best answer. Regardless, when you get a result, make sure you share it with us.

6th of July 2001 (Fri), 16:33
Okay. I played around with my camera some more, and I have an observation. If I have a back-lit subject and I use either spot metering, or center-weighted metering, and focus on the individual, the 420ex will fire, and I will horrifically over-expose the person.

If, however, I point the camera at the more heavily lite background, and do an exposure lock (or half-button if focusing isn't an issue), and then recenter on the under-exposed forground, I get a fantastic picture.

What's up with this?

It appears that the camera exposure algorithm, and the flash exposure algorithm are operating in an additive fashion, each thinking they are solving the other's problem. The result is a "double" exposure.

Can someone else play around with this and verify that I am not imagining things? It seems really stupid that I have to exposure lock on the background, an focus lock on the foreground to get a decent picture.


8th of July 2001 (Sun), 13:46
Greetings All,
I a newbie here to the forum and a recent G1 owner with the 420EX too. (Pekka's site helped clinch my decision).

This may be a moot point but have you upgraded your firmware to version The text states it corrects underexposure issues but ... worth a try?

I'll be watching for this phenomenon and doing some experimenting (Mikes ideas) myself and report my results here.


13th of July 2001 (Fri), 14:24
I've got the 420EX and G1 as well. In my experience, when the subject is very close to you (

15th of July 2001 (Sun), 07:04

Yeah. I'm at (which is the version that had the flash fix).


It just seems weird to me that if there is exposure information going back and forth between the Flash and the Camera, that it can't get the exposure right. I would think that there should only be a problem if we are up against the camera's boundaries (i.e. we are shooting at f8.0, and the flash can't go any lower).

My third problem (works in auto, doesn't work in P), was the most vexing of the three issues. I haven't quite figured it out yet. I can't reproduce it reliably all the time. It seems to come & go.


20th of December 2001 (Thu), 13:18

I'm using G1 and 550ex and have the same problem, however, I found that if you press '*', flash will fire with low power to do metering, and then if you snap the picture, flash will fire with much lower power and exposure will be correct. You might also want to use spot metering to compensate for highlights...

Hope this helps,


20th of December 2001 (Thu), 16:32
Miro wrote:

I'm using G1 and 550ex and have the same problem, however, I found that if you press '*', flash will fire with low power to do metering, and then if you snap the picture, flash will fire with much lower power and exposure will be correct. You might also want to use spot metering to compensate for highlights...

Hope this helps,


i believe it is related to the fact that G1 focus tell the flash that the subject is a lot further than it is

forget about spot or average metering - G1 focusing has always been a problem

it just would not comply and still go for the brightest in the subject matter

when you overexpose, look at the subject distance - i bet that it is further away than it should

my temporary solution: shoot with P and manual focus and then with full auto

i know it is wrong

but i have not figured it out yet

daniel at danielchtong@yahoo.com

21st of December 2001 (Fri), 11:45
I've done quite a bit of experimenting with this issue, because it infuriated me no end.

You don't mention whether you're using Av, Tv, P or M to set the exposure, but here's what I've come up with. P mode will always overexpose with flash, unless you set the flash compensation. Even so, as someone indicated, the camera generally selects 1/60 which is ridiculous.

Av and Tv work similar to P, though Tv is a bit better if you force it to 1/250-1/500.

The best is to set the camera to M. Set the speed between 1/250 and 1/500. Then, you can adjust the aperture according to the amount of background light and the distance to the subject. If your background is dark, a larger aperture will tend to light the subject, but not much of the dark background. A smaller aperture will allow the light to go farther into the background.

Using this method, nearly all my flash exposures are correct.

Play with it and see if your experience is similar to mine.

Mike K
27th of December 2001 (Thu), 15:06
I agree with Jrobbins that the mode choice is very important. In Av and Tv mode the camera will meter for fill flash. Thus in Av, when you have a backlit subject it will meter (or spot meter if you choose that option) for the center, and if that is dark, the camera will choose a very long shutter speed (up to 1 sec!). On the G-2 Canon "fixed" that by not allowing the shutter to go longer than 1/60 in Av with the flash on. Thus on the G-1 Av is not a very useful mode.
I generally use P mode with a 420ex and almost always bounce if indoors. a Lumiquest 80/20 or Stofen omnibounce diffusers also help. Use flash compensation for overexposure.
If you really must stop some action, the g-1 will sych up to 1/250 but no faster. In Tv with the flash on, if you set the shutter to faster than 1/250 (like 1/1000) the camera will fire at F8 and 1/250. This is commonly known as the F-8 flash trick and can be useful for some situations, like reducing over exposure for macros, etc. On the G-2 there are incremental settings leading up to F-8, 1/250, but on the G-1 there are none.
Flash in the Manual mode works well when you really want to control your camera, however the hassle with Manual is that the LCD gives you something like a dof preview. Thus if it is dark (and why else would you be using a flash?) the shutter and apeture values will give you a very dark LCD. It may be too dark to compose with, in which case you may need to flip back and forth between Av an M to compose then shoot, respectively. The other hassle with M is that the flash will fire with full intensity all the time.
Mike K

5th of January 2002 (Sat), 04:33
I have had exactly the same problem with my Pro90IS too! (see Pro90IS forum)

While shooting in P-mode (which is supposed to be the most convenient mode other than Auto), I have to set my inbuilt flash exp compensation to -2 in order to get correctly exposed human subjects.

BTW, how does one obtain the correct exposure metering in Manual mode? The brightening/darkening of the LCD doesn't really help much in determining the exposure of the final image.

5th of January 2002 (Sat), 15:47
Must admit I had the similar problem with the G1/420EX over-exposure (mainly when dark/night) but on upgrading the firmware to the current ver .02, the problem APPEARS to have gone! The images are now more balanced.