fill flash issues

I've been searching, but don't know how to hook this one. I have a new 580ex ii flash. I wanted to do some test shots with using a fill flash to light the background. With the 580 set to ETTL, I shoot. The fill flash is optically fired. The problem is that the picks are too dark. When I use just the 580, the picks are correctly lit. I just want to have some nice back lighting. Help please

Why not just shoot manual?

You mean you're using an optical slave? If so the ETTL preflash is triggering it before the shutter's open. Put the 580 on manual.

If not... more details required.

I haven't tried the manual mode yet. I'm still feeling this flash out. Would the flash still send the pre-signal if I'm not shooting wirelessly?

- You say you are wanting to use "fill flash on the background". Normally when people say "fill flash" they are talking about light to fill in shadows that are on the subject.

- Whenever you use a flash in ETTL mode there is always a preflash. The way that ETTL works is that it fires a pre-flash, watches the scene to see how much light is reflected back "through the lens" and chooses the power level of the flash to correctly light the scene based on that meter reading. When you use an optical trigger to fire a remote flash this pre-flash will trigger the remote light. There are some optical slaves that are "digital compatible" and are designed to ignore the pre-flash.

I'm not trying to get answers from dicks OK. I'm sill learning new equipment and was not sure exactly what was going on. Isn't what this site is about? We are not all pros. I've been using a vivitar 285 for the past few years and was able to finally set the money aside for myself to by a new flash. The manual doesn't tell everything.

tim wrote in post #10496560
That really depends wtf you're talking about. Since you don't really know what you're doing, or the terminology, you're not communicating your thoughts well.

Like I said, just shoot manual. Optical slaves are fine in manual, and you need manual anyway if you use radio slaves.

Thank you. That answers what I needed. I want a lit white background is what I was trying to get across. The 580 is for the main body of the picture.

krb wrote in post #10496567
- You say you are wanting to use "fill flash on the background". Normally when people say "fill flash" they are talking about light to fill in shadows that are on the subject.

- Whenever you use a flash in ETTL mode there is always a preflash. The way that ETTL works is that it fires a pre-flash, watches the scene to see how much light is reflected back "through the lens" and chooses the power level of the flash to correctly light the scene based on that meter reading. When you use an optical trigger to fire a remote flash this pre-flash will trigger the remote light. There are some optical slaves that are "digital compatible" and are designed to ignore the pre-flash.

My apologies, I didn't mean to come across as rude, I considered my post merely informal, but I needed more smiles. I forget people have different communication styles, and things translate differently to different parts of the world.

Most of the information you needed was in my first post, it was just a little brief. Have a read of the FAQ about EOS flash, then you'll understand the basics. That will teach you about ETTL, preflashes, how slaves work, etc.

In brief, if you're using optical or radio triggered flashes you need to work in manual flash mode. There are exceptions, but they're not important right now. If you just have one flash on your camera ETTL is fine, and works well, once you understand its quirks.

Once you've had a read of the resources, especially the EOS Bible, i'd be happy to help more

Thanks. I did not fully understand the ETTL pre flash. I thought it was only for wireless. That fixed my problem

AFAIK all modern flash systems are guess and check. They put out the preflash and see how much light comes back, and depending on that they then put out the full flash at whatever power is required for a good exposure. Since the metering is done Through The Lens it uses the current lens aperture and the sensor ISO, hence the TTL moniker.