New SLR owner, flash question

[learjet035]

One thing I used to do was use a lot o flash outdoors for snapshots of people in daylight conditions. Seemed to always balance out the person with the background. On my trip I had a bunch of time to experiment with different stuff, but one thing I came across was that sometimes I was not able to get the flash to go off. I would hit the flash button but it wouldn't pop up, or it would popup but not fire. I am sure it was me so. I am thinking that I may have had it on the full auto setting, but I do remember doing a bunch of AV setting shots as well. Am I missing something, any tips, or advice, would be great. I also read (I think) that you had some control over the amount of flash that would fire. Is this correct?
See the pic below, what do you do while shooting strongly backlit subjects?

[cmM]

if you're in auto mode, then the flash fires whenever it finds it necessary to.

If you're in AV mode, the flash fires if you're under the max sync speed (1/250?not sure on the rebelXT)

[learjet035]

can you force flash?

[cmM]

can you force flash?
not the built in flash... you could , and external one like 550EX

[Phil V]

can you force flash?

Yes, if you're under the sync speed in P, AV or TV mode and pop up the flash it will fire.

[learjet035]

so here is an example. In my old sony point shoot I just turn the flash on an it would fire here and the pic would look way better. No DOF but you could see my girlfriend much better. What is the sync speed? How would I know if I am under it? Thanks

[hamm3r]

I too am interested in the answers to his questions. Anybody know?

I would also like to add another question. I am using the Sigma EF 500 DG Super Flash EO-TTL with my 300D. I seemed to have to put it into manual mode to get the fill-flash to work. Is this the best way to go about doing this or should I be working on adjusting the "max sync speed" (which I never heard of).

And also, where can I read more about what "flash exposure compensation" is and how to use it with flash?

[hamm3r]

I discovered the "EOS Flash Bible" sticky ( http://photography-on-the.net/forum/showthread.php?t=64504&highlight=flash+bible ) and have read through a good amount of it, but there are a lot more links to read.

Here's what I learned so far (hopefully someone with knowledge/experience can tell me if I am right or wrong).

What I have learned so far is that if the shutter speed is very fast, then it does not leave enough time for the flash to go off (what this exact speed is on my 300D, I do not know yet, and am still trying to find out how to get this information). Stopping down would help, but could have an undesireable affect on your DOF. The camera supports an "FP" mode which I believe fires the flash more than once in order to allow you to maintain your open aperture/shutter speed (as long as your flash also supports it).

Now I just have to discover how to get the camera into FP mode so that I do not have to put the flash into manual mode.

[cmM]

Yes, if you're under the sync speed in P, AV or TV mode and pop up the flash it will fire.
:o
I stand corrected
I guess it shows ive never used the built in flash

[hamm3r]

Here's the rest of the information:

FP mode (o/w known as high-speed sync mode) is NOT available using the built in flash.

The flash on the Sigma or Canon EXnnn can be put into the FP mode in order to provide this feature.

Now I just have to experiment with it.

[robertwgross]

so here is an example. In my old sony point shoot I just turn the flash on an it would fire here and the pic would look way better. No DOF but you could see my girlfriend much better. What is the sync speed? How would I know if I am under it? Thanks

You don't identify which camera you are using, so we cannot tell you what the maximum sync speed is for it. Typically, it is a shutter speed of around 1/200 or 1/250. The manual for your camera identifies what the maximum sync speed is.

Put simply, if you set the speed to 1/500 and attempt to flash, if the camera allows it at all, you will get part of the frame illuminated by flash and part of it dark. If you set at or below the max sync speed, like 1/100, then the entire frame is flash illuminated. Some cameras will prevent you from doing something stupid, and other will not.

---Bob Gross---

[robertwgross]

I am using the Sigma EF 500 DG Super Flash EO-TTL with my 300D. I seemed to have to put it into manual mode to get the fill-flash to work. Is this the best way to go about doing this or should I be working on adjusting the "max sync speed" (which I never heard of).

You cannot adjust the maximum sync speed of a camera. It is built in. There is one number, and it is normally mentioned in the user manual for your camera.

For 300D, it is 1/200 (manual page 80).

---Bob Gross---

[Redbird_xo]

Put simply, if you set the speed to 1/500 and attempt to flash, if the camera allows it at all, you will get part of the frame illuminated by flash and part of it dark.
---Bob Gross---

I think d-slr will do a "step-down" to whatever the higher sync speed is so that the flash will fire and a picture will be taken. The partially illuminated and partially dark frame situation happens with the film cameras. Please correct me if I'm wrong. ;)