Camera's light meter?

[Skid]

When I was just playing around shooting my wife, I had my flash mounted off camera, connected via a PC Sync cord, @ around 1/64th power, through an umbrella pretty close to her face. I was shooting in M on my camera too, using a nifty fifty lens. I was around 1/50th SS, and I think around f2.8-f3.5, my light meter was showing like -2 stops, but my photos came out properly exposed - is this because my camera doesn't know about the flash being connected, as it's just a "dumb strobe" ? If so, is this just a mere guessing game? I figure, after reading numerous posts that the using the flash manually is a trial and error game until you know what you're doing and can guess pretty accurately, but is this the same as when shooting on your camera - knowing when and how much to under expose by?

Is there some rule of thumb on how much to underexpose if this is the case?

Thanks again,
chris

[TheHoff]

You've got it-- you're in M and firing with a dumb PC cord. That cord just sends the electrical signal down the wire telling the flash to fire; it has no idea how much light the flash is putting out nor does it try and tell it how much to use. If you were using an E-TTL connection (ST-E2 or the OC-3 cord) it would be different as they use 2-way communication with the camera, using pre-flashes to determine how much flash will be used.

It is a guessing game until you get a handheld flash meter. At least with digital you can shoot as much as you like and see the results instantly, right?

[tim]

The camera has no idea about any flash connected. Manual flash is either trial and error, or you use a light meter.

Rule of thumb is to leave enough time for trial and error. Take a guess, it takes 20 seconds MAX to refine if you know anything about light. Say your first shot is all white adjust either the camera or the storobes 4 stops in the correct direction. If it's just a bit bright turn either the strobes down or the flashes up.

Easy stuff.

[Skid]

Cool, thanks just wanted to make sure :)

[SkipD]

There's another thing you need to know. When using manual flash for lighting, the shutter speed makes absolutely no difference to the flash exposure. You cannot use a shutter faster than the "max sync speed", though, or part of your image will be cut off.

The only advantage in using slower shutter speeds with flash is that you get more exposure from the ambient light that way. You choose a faster shutter speed to minimize the effect of ambient light relative to your flash.

Adjusting the aperture (and, of course, ISO) is the only thing that affects flash exposures. You could take a series of shots with the same aperture and ISO but a variety of shutter speeds and you'll see that this is correct.

[Skid]

Oh yes, forgot about that! Thanks, I read something about it in the eos flash guide on photonotes.org

cheers :)

[Papa Carlo]

The camera has no idea about any flash connected. Manual flash is either trial and error, or you use a light meter.

Rule of thumb is to leave enough time for trial and error. Take a guess, it takes 20 seconds MAX to refine if you know anything about light. Say your first shot is all white adjust either the camera or the storobes 4 stops in the correct direction. If it's just a bit bright turn either the strobes down or the flashes up.

Easy stuff.
It became trial and error only lately with advances of digital. In older days we were quite happy with aperture/distance charts glued to the flash.
The most experienced ones could very quickly calculate the required apperture from the guide number and distance.

[TheHoff]

It became trial and error only lately with advances of digital. In older days we were quite happy with aperture/distance charts glued to the flash.
The most experienced ones could very quickly calculate the required apperture from the guide number and distance.

I was going to mention auto-thryistors, etc, but thought it was moot these days :)

[tim]

It became trial and error only lately with advances of digital. In older days we were quite happy with aperture/distance charts glued to the flash.
The most experienced ones could very quickly calculate the required apperture from the guide number and distance.

Water used to be hauled out of wells by hand, we don't do that any more either :p

[Titus213]

Water used to be hauled out of wells by hand, we don't do that any more either :p

Actually, in large parts of the world they do....:lol:

[PacAce]

It became trial and error only lately with advances of digital. In older days we were quite happy with aperture/distance charts glued to the flash.
The most experienced ones could very quickly calculate the required apperture from the guide number and distance.
I find your post above very ironic considering it was only a few days ago you said this about using guide numbers, aperture and distance in determining flash exposures:


That's the beauty of working with guide numbers and subject distances. It doesn't matter what the subject or the background colors are or how many subjects are in the picture. Of course, there will be a slight difference in exposure if you are taking a picture outdoors where there are no reflectivie surfaces such as wall versus shooting indoors and that has to be accounted for if you're outside.

When using multiple flashes, you'll need to use the guide number of the combined flash outputs to determine the flash exposure but the principle is still the same. The thing is, you have to do the computation yourself instead of letting the flash do it because there are more than one flash involved in a multi-flash setup (obviously).
No it is not beauty, it is a guesswork. You do need a light meter in the a/m situations if you are concerned about ther results of your work. The guide number just gives you a figure that is applicable to the most common appoximation.

[Jim M]

When I was just playing around shooting my wife, I had my flash mounted off camera, connected via a PC Sync cord, @ around 1/64th power, through an umbrella pretty close to her face. I was shooting in M on my camera too, using a nifty fifty lens. I was around 1/50th SS, and I think around f2.8-f3.5, my light meter was showing like -2 stops, but my photos came out properly exposed - is this because my camera doesn't know about the flash being connected, as it's just a "dumb strobe" ? If so, is this just a mere guessing game? I figure, after reading numerous posts that the using the flash manually is a trial and error game until you know what you're doing and can guess pretty accurately, but is this the same as when shooting on your camera - knowing when and how much to under expose by?

Is there some rule of thumb on how much to underexpose if this is the case?

Thanks again,
chris
Your in-camera light meter will not tell you anything about the flash, no matter what. Yes, the camera meters it in ETTL, but it doesn't tell you what it is doing. The camera meter only tells you about ambient light.