Help with 10D pre flash

[mthinaz]

I am trying to use a flash slave with my 10D. The problem is I can not shut off the "pre flash" using the built in flash.

I thought it would be C.Fn 5....AF-assist beam/Flash, but I guess I was wrong. :( Red eye is also shut off.

Yes I know I would be better off with Radio Slave, but.......

Thanks

MTHinAZ

[PacAce]

I am trying to use a flash slave with my 10D. The problem is I can not shut off the "pre flash" using the built in flash.

I thought it would be C.Fn 5....AF-assist beam/Flash, but I guess I was wrong. :( Red eye is also shut off.

Yes I know I would be better off with Radio Slave, but.......

Thanks

MTHinAZ

Unfortunaely the built-in flash only works in E-TTL mode and that means it's always going to fire a preflash. There's no way of getting around that, I'm afraid.

[jcsorensen]

There is actually a trick you can use, but it is not always convenient, but will work in a pinch. You can push the * button when the flash is up, and the pre-flash will fire to achieve a flash exposure lock. Your slave will fire at that time. Give the slave a chance to re-charge and take your picture with the FEL still active. The camera will not fire the pre-flash when you take the picture because the flash exposure has already been determined (the purpose of the pre-flash). You may have to tell the subject to disregard the first flash, thus the inconvenience, but again, it works.

[mthinaz]

Leo,

Thank for your reply.

[robertwgross]

Unfortunaely the built-in flash only works in E-TTL mode and that means it's always going to fire a preflash. There's no way of getting around that, I'm afraid.

Can't you switch the camera over into Manual exposure mode? I would think that would inhibit the pre-flash. Of course, then metering gets tricky.

---Bob Gross---

[daveh]

With Canon flash systems, manual vs. auto are independent choices for the camera (ambient exposure) and the flash exposure. I use the camera in manual with the flash on Auto all the time. The metering isn't tricky at all since the flash is still auto-exposed which is often all you care about. (ie non-fill-flash situations.)

As long as the flash is running in auto (the only choice for the built-in flash) then you get a pre-flash.

[PacAce]

Unfortunaely the built-in flash only works in E-TTL mode and that means it's always going to fire a preflash. There's no way of getting around that, I'm afraid.

Can't you switch the camera over into Manual exposure mode? I would think that would inhibit the pre-flash. Of course, then metering gets tricky.

---Bob Gross---

Setting the camera on manual does not set the flash on manual. The flash will still fire automatically and set the flash exposure for a good exposure, as it does when the camera is in one of the programmed modes. Of course, depending on what the aperture is and the distance of the subject from the camera, the flash may not be able to get a good exposure but that would be true even when the camera is set to programmed mode.

And needless to say but, yes, the preflash will still fire even when the camera is in manual mode.

[robertwgross]

And needless to say but, yes, the preflash will still fire even when the camera is in manual mode.

I can't think of a reason why Canon would do it that way. What would the pre-flash do for the exposure if the camera is set on manual exposure?

---Bob Gross---

[daveh]

[quote=PacAce]
I can't think of a reason why Canon would do it that way. What would the pre-flash do for the exposure if the camera is set on manual exposure?


It's very handy. The flash still does auto flash exposure via E-TTL when the camera is in Manual. This is much like using the old non-dedicated flashes which had their own metering systems - but with the advantages that the metering is through the lens and you don't have to turn a dial on the flash to tell it what aperture you've selected on the camera.

I use my Canon flashes in this way most of the time. As soon as you set the camera for automation, the flash goes into a fill/balance mode which I don't use as much. With the camera in manual, you can pick any aperture and shutter speed (up to 1/200th) you like and the flash is required to comply (if it can). In auto camera modes you tend to get slow(er) shutters and wide open apertures because the camera/flash want to balance the ambient light as much as possible.

[slin100]

And needless to say but, yes, the preflash will still fire even when the camera is in manual mode.

I can't think of a reason why Canon would do it that way. What would the pre-flash do for the exposure if the camera is set on manual exposure?

---Bob Gross---
Why wouldn't you expect it to work this way? The camera's exposure mode (Av, Tv, P, M) never affects flash exposure. It only affects ambient exposure.

There is no way to set an absolute flash power setting (i.e. 1/1, 1/2, etc) from the camera. The only thing available is FEC. But FEC is always relative to a metered pre-flash exposure. That's a fundamental way in which ETTL works.

[slin100]

I use my Canon flashes in this way most of the time. As soon as you set the camera for automation, the flash goes into a fill/balance mode which I don't use as much.
Unless disabled by C.Fn 14, auto reduction of fill flash applies in any exposure mode, including M. The auto reduction occurs at light levels above EV 10 @ ISO 100.

[daveh]

[quote=daveh]
Unless disabled by C.Fn 14, auto reduction of fill flash applies in any exposure mode, including M. The auto reduction occurs at light levels above EV 10 @ ISO 100.

I use M because I frequently want high flash output at low ambient light levels. At higher levels, it's rarely an issue for me.

[robertwgross]

The flash still does auto flash exposure via E-TTL when the camera is in Manual. This is much like using the old non-dedicated flashes which had their own metering systems - but with the advantages that the metering is through the lens and you don't have to turn a dial on the flash to tell it what aperture you've selected on the camera.


Of course. I was thinking of external flash on manual, but this thread is for internal flash. The internal flash can modulate its intensity (actually by duration) with pre-flash metering and then use this for the main flash. It just seems like this would complicate the camera's manual exposure.

---Bob Gross---

[robertwgross]

Why wouldn't you expect it to work this way?

Because about 99.5% of my flash photography is with an external flash, so I begin to forget about what the internal flash can do.

---Bob Gross---

[daveh]

It just seems like this would complicate the camera's manual exposure.


Not at all. In most cases, I pick 1/200th, and an aperture based on desired DOF and distance and then the flash adjusts its output to make that work. The External Canon flashes work this way by default as well - although they typically have other options including full manual.

[robertwgross]

In most cases, I pick 1/200th, and an aperture based on desired DOF and distance and then the flash adjusts its output to make that work.

I've thought of it the other way around. The internal flash puts out some amount of light, and the shutter and/or aperture are quickly set to produce the correct exposure. I didn't think of it with the flash putting out a variable amount of light to get the exposure according to shutter and/or aperture. But then, as I said, I do nearly all of my flash work with an external flash.

---Bob Gross---

[PacAce]

Why wouldn't you expect it to work this way?

Because about 99.5% of my flash photography is with an external flash, so I begin to forget about what the internal flash can do.

---Bob Gross---

The 420EX works the same way, too, as the internal flash. It's only with the 550EX where you can actually overide the "auto" flash exposure and set it to manual. But I do agree with you, Bob, about the E-TTL flash behaving "oddly" compared to the old traditional way of shooting with a flash with the camera set to manual.

[robertwgross]

The 420EX works the same way, too, as the internal flash. It's only with the 550EX where you can actually overide the "auto" flash exposure and set it to manual. But I do agree with you, Bob, about the E-TTL flash behaving "oddly" compared to the old traditional way of shooting with a flash with the camera set to manual.

Although I have both one 550EX and one 420EX, I virtually never use the 420EX.

"Old traditional way"? How old are we talking about? You mean like the old auto-thyristor flash units (state of the art about 25 years ago)?

---Bob Gross---

[PacAce]

The 420EX works the same way, too, as the internal flash. It's only with the 550EX where you can actually overide the "auto" flash exposure and set it to manual. But I do agree with you, Bob, about the E-TTL flash behaving "oddly" compared to the old traditional way of shooting with a flash with the camera set to manual.

Although I have both one 550EX and one 420EX, I virtually never use the 420EX.

"Old traditional way"? How old are we talking about? You mean like the old auto-thyristor flash units (state of the art about 25 years ago)?

---Bob Gross---

Yup! :mrgreen:

[daveh]

"Old traditional way"? How old are we talking about? You mean like the old auto-thyristor flash units (state of the art about 25 years ago)?


The real traditional ways are using the flash guide number and doing math to determine and aperture from the distance or firing the flash and using a flash meter to tell you the aperture.

Those "old auto-thyristor flash" aren't that different from using one of the Canon flashes with the camera in Manual - except that they read through the lens rather than their own sensor and you don't have to manually communicate the aperture and film speed info between the camera and flash. Other than that it's basically the same idea - the camera is does what it's set to do and the flash cuts off the light when there's enough to make a reasonable exposure for the camera settings.

I also had a Canon flash in the 70s that had a ring that mounted on the lens. That flash used distance ONLY for determining flash output. It worked very well but you needed different rings for different lenses, which was a bother.

[Jon]

I also had a Canon flash in the 70s that had a ring that mounted on the lens. That flash used distance ONLY for determining flash output. It worked very well but you needed different rings for different lenses, which was a bother.

Ah, yes, the Speedlite 133. I have one of those for my F-1n and FTb, along with the accessory shoe for the F-1. Anyone know where to get a replacement for the big (MH?) mercury cell it took along with the PX13/625? It also only worked with a very few lenses, even if you had the right-sized ring.

[scottbergerphoto]

It makes perfect sense for the ambient and flash metering to be totally independent. If that was not the case then you would have no control over how the background is lit in a flash shot or how much ambient light is included in your picture. Sometimes you want more ambient light, sometimes you want less and sometimes you want the busy background to go black. You also would not be able to adjust the ratio between ambient light and flash except by adjusting the flash.
I usually shoot with the camera in M Mode and the flash in ETTL. This works using the 10D's built in flash or any external flash.

A word about so called "old fashioned Auto flash". My Quantum T2D has Auto flash and it's not old. If you are taking a series of pictures from the same distance, Auto (thyristor controlled) Flash is very consistent. Some of Nikon's high end flashes have Auto Mode. All the bells and whistles of ETTLII doesn't necessarily mean you will get better pictures then an Auto flash or a Manual flash. It depends how you use them.
Scott

[robertwgross]

A word about so called "old fashioned Auto flash".


We called it the old traditional way. There's often nothing wrong with traditions.

---Bob Gross---

[picnic]

And needless to say but, yes, the preflash will still fire even when the camera is in manual mode.

I can't think of a reason why Canon would do it that way. What would the pre-flash do for the exposure if the camera is set on manual exposure?

---Bob Gross--- With ETTL, the flash exposes for the subject or whatever is under the AF point (or, in certain situations, such as setting the C.FN 4 on 2 where the metering is done with shutter button and AF is with * button--and by pressing and releasing the * button you will get more of an overall/evaluative flash). Setting the camera in manual only affects the overall exposure--but not the FLASH exposure which is metered differently.

Try this URL http://photonotes.org/articles/eos-flash/

Its best to experiment with this yourself rather than believe us---then you will see that recomposing, for instance, will result in a different flash exposure--all with the camera set to manual. You can, of course, put the 550EX in manual also--but then you lose the effect of ETTL and you have to experiment a bit to see at what power you need to set the 550EX.