Canon DSLR metering with 430EXII

dnme

I'm just wondering,

When you connect an external flash to your canon, (in my case 60D and 430EXII), how is metering supposed to work?

I am using manual mode, and flash is set to ETTL. But the addition of the flash does not seem to be affecting the meter. It reports an underexposure even though the flash fires and I get a spot on exposure / histogram. Its as if the camera is unaware of the flash as far as metering is concerned but it is still firing it. I would have though that when I attach the flash, and set it to ETTL, the meter would include it in its exposure calculation ??

What am I missing?

Many thanks

DaireQuinlan

dnme wrote: »

I'm just wondering,

When you connect an external flash to your canon, (in my case 60D and 430EXII), how is metering supposed to work?

I am using manual mode, and flash is set to ETTL. But the addition of the flash does not seem to be affecting the meter. It reports an underexposure even though the flash fires and I get a spot on exposure / histogram. Its as if the camera is unaware of the flash as far as metering is concerned but it is still firing it. I would have though that when I attach the flash, and set it to ETTL, the meter would include it in its exposure calculation ??

What am I missing?

Many thanks

Nothing, you've got it pretty spot on. The flash portion of the exposure is independent of the ambient portion. So long as your exposure speed is at or under your flash sync speed and TTL flash metering is on then the camera will do that quick preflash which provides it with the correct exposure for the flash, irregardless of whether the meter is reading under for the ambient portion.

If I'm shooting solely with flash I normally just stick my shutter speed on 1/250, set my aperture to something appropriate, and trust that the TTL flash metering will get the shot right.

dnme

DaireQuinlan wrote: »

Nothing, you've got it pretty spot on. The flash portion of the exposure is independent of the ambient portion. So long as your exposure speed is at or under your flash sync speed and TTL flash metering is on then the camera will do that quick preflash which provides it with the correct exposure for the flash, irregardless of whether the meter is reading under for the ambient portion.

If I'm shooting solely with flash I normally just stick my shutter speed on 1/250, set my aperture to something appropriate, and trust that the TTL flash metering will get the shot right.

Do you mean that the 430 has it's own meter? Does it meter independently of the camera and decide how much flash to fire? Why don't the two talk to each other via TTL ?

DaireQuinlan

dnme wrote: »

Do you mean that the 430 has it's own meter? Does it meter independently of the camera and decide how much flash to fire? Why don't the two talk to each other via TTL ?

Digital TTL flash metering generally (the nikon system anyway AFAIK, I assume the canon system is similar) fires a pre-flash before the actual exposure, which allows the camera meter to work out how what the flash duration should be to get the exposure right. Then when the actual exposure is made that's used to control the flash duration. So the camera & flash are communicating with one another to work it out.

The older film TTL flash I think had some advantages over digital, in that there was no pre-flash necessary, the flash exposure was read during the exposure by a separate meter cell measuring off the film plane.

dnme

It's making no sense to me. The meter in my viewfinder is telling me that the image is way under exposed, yet when I take the shot its fine. If I obey the meter, I am ending up with silly shutter speeds like 1/4 sec etc.

If I put the camera in Program mode, I get a meter reading of f4 1/60th sec
If I then put it in Av aperture priority, the meter reads f4 1/5th second (pointing at the same scene / light).

Now if I remove the flash unit altogehter and use Av mode without the built in flash, the meter reads the same as above, f4 1/5th second.

I'm so confused by all this now. No idea what is going on.

How are you supposed to meter when using the external flash unit without guess work?

DaireQuinlan

The meter in your viewfinder, as I point out above, is metering the ambient light in the scene. If you have a flash attached and it's using TTL metering then only at the point that you fire the shutter is it going to do its pre-flash to determine the correct flash exposure.

Sticking the camera into program mode ? I don't know, maybe it's adjusting the ISO up to get reasonable handheld shutter speeds or something.

Metering for flash without the guess work generally requires a shed load of guess work. Or a flash meter :-D I have a sekonic that I use to meter for flash if I'm shooting some camera without TTL, you attach the flash to the meter, hold the meter beside the subject if you're metering incident (which you'd be doing 9 times out of 10) and it fires the flash and provides a suitable aperture to use at a given iso.

Alternatively you can use aforementioned guess work if you want, read up on 'Guide numbers' for a gander. They're the primary reason TTL flash was invented

dnme

Thanks for the replies DaireQuinlan

I'm completely lost now. I imagined the flash unit via TTL would give me a correct metering through my viewfinder. I imagined it would fire a pre or test flash when I pressed the shutter half way or whatever. As it is, I'm left with incorrect metering. Hugely confusing. Surely these cameras and flash units are smarter than this? surely ????

pixbyjohn

Accept what Daire says because its true. Hard to understand but it works as he says. The camera will set the exposure after the shutter is opened and reads the reflected light through the lens. You won't see it on your camera's lightmeter before the shot is taken.

stuar

dnme wrote: »

I'm just wondering,

When you connect an external flash to your canon, (in my case 60D and 430EXII), how is metering supposed to work?

I am using manual mode, and flash is set to ETTL. But the addition of the flash does not seem to be affecting the meter. It reports an underexposure even though the flash fires and I get a spot on exposure / histogram. Its as if the camera is unaware of the flash as far as metering is concerned but it is still firing it. I would have though that when I attach the flash, and set it to ETTL, the meter would include it in its exposure calculation ??

What am I missing?

Many thanks

I've a Canon 1Ds and a 550EX flash, when I use it as you say, camera in manual mode, flash with ETTL set and say 1/250th f8, the light meter through the viewfinder always stays in centre (correct exposure) no matter what light is actually coming through the lens.

If I turn the flash off the light meter shows under-exposure, turn the flash back on and light meter indicates correct exposure again.

Also on the display on the back of the flash a range in feet is displayed depending on apature/speed set on the camera and moves up and down as f/stop is changed. It doesn't use a preflash.

I'm not familiar with 60D but I'd imagine your camera/flash should work the same way, maybe one of the connections is dirty, but it seem's your camera and flash aren't communicating too well.

DaireQuinlan

stuar wrote: »

I've a Canon 1Ds and a 550EX flash, when I use it as you say, camera in manual mode, flash with ETTL set and say 1/250th f8, the light meter through the viewfinder always stays in centre (correct exposure) no matter what light is actually coming through the lens.

If I turn the flash off the light meter shows under-exposure, turn the flash back on and light meter indicates correct exposure again.

That sounds a little weird. Do you have some option set on your body ? Or shooting in some program mode ? How are you supposed to meter for the ambient portion of your scene if your camera is zero-ing the meter indication ? Is it maybe only showing you the flash exposure compensation ?

Also on the display on the back of the flash a range in feet is displayed depending on apature/speed set on the camera and moves up and down as f/stop is changed. It doesn't use a preflash.

All modern digital TTL flash systems use a pre-flash to determine the correct exposure. The distance changing on the back is something you'd normally see if you had the flash set to manual and you were adjusting that way, so it's kinda strange to show it in TTL mode as the flash power will be adjusted automatically by the camera when it does its pre-flash.

stuar

DaireQuinlan wrote: »

That sounds a little weird. Do you have some option set on your body ? Or shooting in some program mode ? How are you supposed to meter for the ambient portion of your scene if your camera is zero-ing the meter indication ? Is it maybe only showing you the flash exposure compensation ?

No custom functions set, no program mode, Manual Mode!

When I did this test lastnight, without flash everything would have been grossly under exposed, with flash powered on the indicator always stayed at correct exposure meaning at point of pressing the shutter the camera knew it would expose correctly no matter what, then fired and exposed correctly both in a dark corner and at the light on the ceiling.

DaireQuinlan wrote: »

All modern digital TTL flash systems use a pre-flash to determine the correct exposure. The distance changing on the back is something you'd normally see if you had the flash set to manual and you were adjusting that way, so it's kinda strange to show it in TTL mode as the flash power will be adjusted automatically by the camera when it does its pre-flash.

I think the 550EX uses the red focus assist light instead of pre-flash (maybe only with certain camera's), I also have a 1D mark II and another 550EX and using that in the exact same way doesn't produce a pre-flash either, actually I don't think I've ever experienced a pre-flash in any shooting mode with either camera.

EDIT:
I did a quick google, and although this is referring to film camera's with 550EX, maybe there is a preflash after all, just I can't see it, I'll quote a couple of replies:

It is very, very difficult to see the pre-flash

and the camera reads the preflash itself. It does this so fast that you can't even tell that there was a preflash most of the time

Hi Thomas, I don't think you should to be too concerned about the preflash when you use normal flash sync speeds. It happens so fast that you will not notice it.

http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=0054BL

EDIT....EDIT.
Daire I did say "no matter what light coming through the lens", this is false, I should have added that the light I was talking about was all below the set exposure value, for fill in, in daylight totally different situation, I expose for the highlight and the flash (normally) gets the fill amount correct.

stuar

DNME:
I'm not sure about 60D and 430EX, but in low light situations I'd imagine your system should work like mine, ie knows the flash is present and indicates that it will expose correctly, although my camera/flash can sync at all speeds upto 1/8000th sec, but I still think there is a lack of communication somewhere between your flash and camera, does the little flash symbol show up in your view finder when flash is cycled and ready to fire?

dnme

@stuar

Yes it does. Apart form that - I'm hugely confused

Guys, are you telling me that the meter is useless when shooting with external flash in low light (say indoors at night) conditions and that it's down to an educated guess?

I do realise that the flash will also meter and compensate but I am really struggling with the concept of a meter telling me a shot will be way underexposed when the final result is not.

stuar

dnme wrote: »

@stuar

Yes it does. Apart form that - I'm hugely confused

Guys, are you telling me that the meter is useless when shooting with external flash in low light (say indoors at night) conditions and that it's down to an educated guess?

I do realise that the flash will also meter and compensate but I am really struggling with the concept of a meter telling me a shot will be way underexposed when the final result is not.

I'm saying your camera and flash ain't communicating properly, I think a mate of mine has a 60D, next time I see him I'll throw one of my flash heads on and see what the story is.

But what you need is somebody with same camera/flash to tell you what happens to them in the same situation you mention.

Daire is good, no doubts, but I think he/she is more familiar with medium format film, I actually nearly sold him/her a pentax 67 a few years ago.

Edit:

It's actually your camera needs to do the guess work, not you, and although showing under exposure it is doing the math correctly. I have a sekonic light/flash meter that I haven't really needed to use since turning to digital, I also use a ST-E2 transmitter that I use sometimes with 2 flash heads set to slave and again give the exact same results in low light situations when one or both are powered on and even using ratio between A and B slave.

DaireQuinlan

stuar wrote: »

Daire is good, no doubts, but I think he/she is more familiar with medium format film, I actually nearly sold him/her a pentax 67 a few years ago.

Really ? I actually have a fairly capable 35mm system, in the shape of an F100 and an SB26. Obviously in TTL mode there are differences, no pre-flash for example, film TTL used to work reflected off the film during the exposure, but the fundamentals are the same.

I've also messed around with canon digital bodies & strobes before, everyone in work who has a camera seems to be a canonista. And in all cases, if the camera didn't give me the correct metering for ambient even with a flash stuck on the top and switched to TTL, I'd be looking for a way to fix it.

I still maintain you have some custom function set on your body or something. The way you're describing your camera body working when a strobe is attached just isn't useful in any way, unless, as I was saying above, it's displaying the FEC or something.

That said, I have no in depth knowledge of specific canon bodies or the intricacies of their flash system so I could well be completely off-base.

mathepac

dnme wrote: »

... When you connect an external flash to your canon, (in my case 60D and 430EXII), how is metering supposed to work?

I am using manual mode, and flash is set to ETTL. ...

From my perspective given the setup you describe, your camera's metering won't work if the camera is set to "manual mode", as aperture priority, shutter-speed priority and full program mode are all switched OFF. It sounds to me like the flash in full ETTL mode makes all the decisions, based on using the initial flash as a test.

The camera in "manual mode" will always indicate a gross under-exposure unless you adjust ISO, aperture or shutter speed to match the scene to be shot.

Rew

Found this quite a good tutorial on flash metering

shaileshbk

Hi Guys, I know this is an old post but thought of sharing my understanding. There are two aspects here that you need to understand

1. Metering through the lens (TTL) - When you use your camera meter it meters ambient light only. It doesn't know or care about the externally attached flash. So basically it says with this iso, with this aperture if you want the image to be exposed correctly use so much of shutter speed
2. Flash output calculation - now you attach your flash to camera hot shoe. ETTL is nothing but passing on the information about how much ISO and how much aperture to be used. If you use pre-flash then it knows the distance of the subject from camera. Accordingly your flash fires calculated amount of flash.
When you use manual mode - it will still pass on this information but only difference is in this case you tell camera that I am going to decide on the shutterspeed as my external light source is connected.

To give an example:
We have following setting:
F2.8
ISO100
If you have in-camera meter reading showing shutter speed of 1 sec

Now you attach a flash, the meter reading will still show 1 sec.

However, at this point I tell camera that I want my shutter speed to be 1/200 as 1 sec shutter speed suggested is not useful for me. But with this shutter speed my image will be totally dark as not enough light coming in. Now I turn on my flash, the information is sent to the camera via hot shoe (i.e., ETTL) and it will fire enough burst to light the subject. What will happen in this case is that the subject will be lit correctly but the areas where the flash is not falling will be dark (i.e., not enough ambient light coming through the lens).

Hope this explains the original question. Having an external meter reader is very useful because in-camera meter reader is blind (can't see) on certain occasions (i.e., when the mirror is up).