Firing Sigma 500DG with built in flash

[OviV]

My Sigma 500 DG Super can be set to slave mode and it will fire when it detects another flash. My problem is that it seems to me that by the time it fires, it is too late since the image has already been exposed. Is there a trick to this? This if with a software-enhanced Digital Rebel, btw.

Ovi

[robertwgross]

Oviv, I don't have a direct answer to your situation. However, let's think about it. If your camera is in one of the normal flash modes, then the pre-flash goes first, the reflected light is measured in the camera, and then the main flash goes (with the right settings).

The pre-flash light might be triggering the external Sigma flash, so it is going off too early (before the main flash and the shutter). So, maybe Sigma is going too early, rather than too late.

If it becomes impossible to solve, you might try to see if you can fool around with your camera's shutter settings to see if you can get any of the Sigma light at all to fall on your sensor. I'm guessing it won't work at all. Just a guess.

I think there are some other Sigma flash guys on this forum, and they probably don't have to guess.

---Bob Gross---

[scottbergerphoto]

Unless your Sigma DG is set to do wireless ETTL, it will be triggered by the preflash of the on camera flash. What does the LCD of the Sigma say when it is set up as slave? How does that compare to when it is in the hot shoe? If it says ETTL in the hot shoe and not as an off camera slave, that's it.

An alternative strategy would be to put a digital hot shoe slave on the Sigma if you can find one that fits. The digital slave ignores the preflash. You would then have to set the output manually on the flash.
Scott

[OviV]

The sigma flash can be set to wireless ETTL but I believe I need another 500 DG or a 550 EX to trigger it as a slave, don't I? I know about the pre-flash but the flash recycles fast enough to be ready when I fire the main flash. The problem is that I do not see the effect of it firing in the resulting pictures. I imagine it is because the flash is firing after the shutter is already closed. I know that it fires because I used a remote to fire the camera while looking at the flash and almost blinded my self in the process.

Ovi

[jcsorensen]

Ovi: I use the same Sigma Flash and have used it quite frequently in the slave mode. I must admit that most times I've triggered it with a manual flash on a synch cord---thus no pre flash. I do believe I have fired it with the built in flash and it seems to work fine there, and that would be with the pre-Flash. The flash is advertised to be fully ETTL compatible and work the same as the 550EX. One test you might want to try is to set the flash up in slave mode, then take a picture of it with the flash on the camera up. If it is synching up, you should get a picture with a very hot flash visible.

Wish I had more to offer.

JC

[vfilby]

Warning: Off topic...

I am looking into flashes and you guys brought the Sigma ef-500DG Super to my attention. Would you guys recommend the flash in place of a 550EX or a 420EX?

Now back to your regularly scheduled programming...

Vince

[scottbergerphoto]

The sigma flash can be set to wireless ETTL but I believe I need another 500 DG or a 550 EX to trigger it as a slave, don't I? I know about the pre-flash but the flash recycles fast enough to be ready when I fire the main flash. The problem is that I do not see the effect of it firing in the resulting pictures. I imagine it is because the flash is firing after the shutter is already closed. I know that it fires because I used a remote to fire the camera while looking at the flash and almost blinded my self in the process.

Ovi
You raise a good point I hadn't considered. In ETTL, the slave flash is NOT fired by a regular flash burst but by a series of light pulses emitted by the Master Flash. I don't believe the internal flash is capable of working as a wireless master. Thus my point above is not relevant. It doesn't matter if the Sigma shows ETTL. You need a 550EX or another Sigma 500DG Super to act as Master.
As to recycling time, unless you're using FEL to fire the preflash and waiting for the flash to recycle before taking the picture, there is no way the flash can recycle between preflash and flash. It's too fast for you to even see.
Scott

[jalafer]

Warning: Off topic...

I am looking into flashes and you guys brought the Sigma ef-500DG Super to my attention. Would you guys recommend the flash in place of a 550EX or a 420EX?

Now back to your regularly scheduled programming...

Vince

I have a Sigma 500, but I can tell you that the plastic quality is very cheap.
In fact my flash has the shoe broken. Now I ordered a 420EX and a external cord, so I can use either the Canon alone in the hot shoe or a combination with the Sigma in the cord as a master and the Canon as slave.

[OviV]

O.K Now I'm confused. I thought the pre-flash was the burst that the camera uses to aid in focusing. Is there another preflash that I don't know about? If it is the focus burst, I can wait before firing to make sure the Sigma has recycled, if it is not then I have more to learn.

Ovi

[vfilby]

I thought that the preflash was a less powerful flash that's fired a split second before the main flash to help set WB.

Vince

[scottbergerphoto]

The preflash has nothing to do with focusing or WB. When you depress the shutter fully but before the shutter opens, the camera fires a preflash which is measured as it reflects off the subject, the camera adjusts the flash output and fires the flash when the shutter opens. It happens very fast. The only way to see the preflash is use 2nd curtain sync with a long shutter speed or hit FEL and then depress the shutter button. FEL fires the preflash.
I suggest you read: http://photonotes.org/articles/eos-flash/
Scott

[robertwgross]

What Scott stated is true. First, you have to get it straight as to how you are trying to sync the whole works.

If you are using the Canon wireless flash system approach, then you have to have one wireless master (e.g. 550EX set to master, or STE2) to "talk to" the wireless slave. Hint: the built in flash does not do wireless master.

If you are not using the Canon wireless flash approach, then you must be trying to use an optical slaving approach. That is OK, but you have to have the right optical slave adapter at the Sigma to get it to ignore the pre-flash and only fire on the main flash.

All of these Canon flash gadgets (e.g. 550EX, 420EX, and built-in) all fire a pre-flash when you are in a normal flash mode. That has nothing at all do do with autofocusing or white balance or anything else. The pre-flash is then measured in the camera and the main flash fires a split second later. Some people claim that only one pop happens. Others claim that two pops happen. Hint: there's two.

Now, despite having all of this technology present in the camera and the flash units, you can shut it all down and shoot a manual flash mode, just like we did twenty years ago.

---Bob Gross---