Back Button focus and E-TTL

Okay, I have a question. When do you see the ETTL pre-flash discharge?

Adharr wrote in post #16808379
Okay, I have a question. When do you see the ETTL pre-flash discharge?

It suppose to happen after pressing the shutter button and just before camera firing actual flash. Not sure how FEL going to work. They just happen at same time (ETTL and flash) for our eyes.

khwaja wrote in post #16808450
It suppose to happen after pressing the shutter button and just before camera firing actual flash. Not sure how FEL going to work. They just happen at same time (ETTL and flash) for our eyes.

You are correct. The pre-flash is normally an instant before the shutter opens. I am trying to figure out if he is seeing the pre flash discharge when he presses the * button to focus, or if it's discharging when he half-presses presses the shutter. That would then tell us if flash exposure lock is even locking in the first place. (Flash exposure lock is kind of like spot metering for the flash power... It uses whatever you have the center spot being pointed over to determine flash power.)

If he sees no pre-flash, then FEL isn't happening. Which means it is just normally flash metering. Then I want him to find out if the flash metering setting was accidentally set to center weighted average from evaluative to account for the random flash powers between shots (Center weighted average flash metering uses the center area, but it's weakness is it takes everything including things like lights and reflections and averages them on a scale of center weighted importance with the area of the frame outside the center. Evaluative flash metering tries to ignore the crazy things like light bulbs and black areas so the flash metering isn't thrown off by them. However the catch is that sometimes the center weighted average method is better for weird lit rooms.)

And also--- just to make sure. The flash is fully recharging between shots, correct??

Scatterbrained wrote in post #16808194
I leave the flash in E-TTL but use the camera in Manual. This way I control the camera exposure (background) and leave the subject up to the flash. Works pretty well more often than not.

I have never used this camera in any other mode than manual. When I bought my first DSLR, I made myself learn how to use it in manual (I went from film to DSLR, so it made a kind of sense at the time), figuring that if I could do that, the other modes would come, but I never got around to them.

Learning the other modes is also on my photodude bucket list.

Adharr wrote in post #16808379
Okay, I have a question. When do you see the ETTL pre-flash discharge?

Hmm... interesting question. I don't know that I have ever noticed it.

Adharr wrote in post #16808554
You are correct. The pre-flash is normally an instant before the shutter opens. I am trying to figure out if he is seeing the pre flash discharge when he presses the * button to focus, or if it's discharging when he half-presses presses the shutter. That would then tell us if flash exposure lock is even locking in the first place. (Flash exposure lock is kind of like spot metering for the flash power... It uses whatever you have the center spot being pointed over to determine flash power.)

If he sees no pre-flash, then FEL isn't happening. Which means it is just normally flash metering. Then I want him to find out if the flash metering setting was accidentally set to center weighted average from evaluative to account for the random flash powers between shots (Center weighted average flash metering uses the center area, but it's weakness is it takes everything including things like lights and reflections and averages them on a scale of center weighted importance with the area of the frame outside the center. Evaluative flash metering tries to ignore the crazy things like light bulbs and black areas so the flash metering isn't thrown off by them. However the catch is that sometimes the center weighted average method is better for weird lit rooms.)

And also--- just to make sure. The flash is fully recharging between shots, correct??

My camera is usually set on Spot metering, though I did play with the other modes yesterday to see if I could notice a real difference with E-TTL.

And yep, the flash is fully recharging. New batteries, and waiting until the unit showed ready between shots.

FWIW: I appreciate folks taking the time to answer my questions. I really do want to learn, and this is helping.

Vetteography wrote in post #16809031
Hmm... interesting question. I don't know that I have ever noticed it.

It is too fast to see by looking at it. They only way to see it is to look through your viewfinder. If you see a flash that is the pre flash. You cannot see the actual flash because the mirror is down at that point. If your flash is on manual you won't see it. People use this method to see if their system is working.

I'll get to the ETTL thing. I have to step out for a bit.

Vetteography wrote in post #16809033
My camera is usually set on Spot metering, though I did play with the other modes yesterday to see if I could notice a real difference with E-TTL.

And yep, the flash is fully recharging. New batteries, and waiting until the unit showed ready between shots.

FWIW: I appreciate folks taking the time to answer my questions. I really do want to learn, and this is helping.

Your cameras ambient light meter has nothing to do with flash so spot, partial, centre- weighted, evaluative do not effect the flash. The flash has not fired and the ambient meter cannot predict flash output. Your camera, no matter what setting it is on is only metering the surrounding areas or ambient light. The flash has a specific job, the camera has a specific job and neither care what the other is doing.

ETTL metering. Your flash to preset to Evaluative. This has nothing do do with your cameras meter when it is in evaluative mode. If you change your cameras metering mode to spot or anything else your flash is still in Evaluative mode.

In Evaluative mode there are multiple metering zones. When you press your butter button half way your camera takes an ambient reading. When you press the shutter all the way the pre flash fires and light is reflected back to the cameras exposure system. The system compares the ambient reading to the light reflected back and isolates the closest object which is typically your subject. ETTL determines the correct exposure based on the isolated object.

You know how your cameras ambient light meter works. If you shoot pure white snow it will underexpose. If you shoot pure black tar it will overexpose. If there is an equal amount of snow and tar in frame then you get a good exposure.

Even though the flash has nothing to do with the cameras ambient meter it's flash exposure system (pre flash) works the same way. I'll use a wedding as and example. A bride alone in a white dress, a groom alone in a black tux and the bride and groom together will all reflect back light differently. ETTL is ball park. This is why flashes have FEC so you can fine tune your exposure based on how the system reads the light that was reflected back. It is just a computer trying to make it's best guess.

I'm not sure if your camera has this but your flash can be set to average. This can only be done via your camera in the flash menus. Again this has nothing to do with your cameras ambient light meter. Average does not isolate the subject, it just averages out the whole scene. Some people say it works better indoors because a bride is usually surrounded by darker light thus it averages out the scene better. Not too good for outdoor shooting.

The last way to alter your flash exposure is by using the FEL button. When you press the FEL button you flash fires. When it fires the system only reads the light reflected back within the spot meter circle area. Some photographers like to meter off skin tones and then have a preset FEC like +1. Similar to you metering off something specific with your cameras ambient light meter when you set it to spot metering. Again FEL has nothing to do with the cameras ambient light meter.

So hopefully this clears things up. Many people like to shoot with the camera on manual. First they get the ambient or background light the way they want it. Then they introduce the flash and it's job is to expose the subject only.

Here are some good videos on the subject.

http://cpn.canon-europe.com …asterclass/cano​n_flash.do

digital paradise wrote in post #16809177
Here are some good videos on the subject.

http://cpn.canon-europe.com …asterclass/cano​n_flash.do

Those videos are very informative, thanks! I didn't know about the differences between E-TTL and E-TTL II.

I also learned that my camera has wireless master capability like the 7D, which was news to me as well.

digital paradise wrote in post #16809164
In Evaluative mode there are multiple metering zones. When you press your butter button half way your camera takes an ambient reading. When you press the shutter all the way the pre flash fires and light is reflected back to the cameras exposure system. The system compares the ambient reading to the light reflected back and isolates the closest object which is typically your subject. ETTL determines the correct exposure based on the isolated object.

This is interesting, especially when thinking about the results I was getting.The video explained that on cameras without a dedicated FEL, it will only hold the spot metering for the flash as long as you hold the shutter down half way, discarding it if you let up. THIS is exactly what I was seeing! With the back-button focus enabled, and the AE/FEL function moved to the shutter button, I think I still need to keep focus engaged (that half-press if it were the shutter button) to lock in the FEL.

I think I need to experiment more.

Might be. Like I said - just a computer trying to make it's best guess. That is why so many people use flash meters and shoot on manual.

A few videos that may be helpful

http://www.youtube.com …ure=feedf#aid=P​-tRnudWsMk

This is studio flash outdoors but the principle is the same.

http://www.youtube.com …ISm7C6fiY&featu​re=related

Vetteography wrote in post #16809257
This is interesting, especially when thinking about the results I was getting.The video explained that on cameras without a dedicated FEL, it will only hold the spot metering for the flash as long as you hold the shutter down half way, discarding it if you let up. THIS is exactly what I was seeing! With the back-button focus enabled, and the AE/FEL function moved to the shutter button, I think I still need to keep focus engaged (that half-press if it were the shutter button) to lock in the FEL.

I think I need to experiment more.

I'm thinking the same thing about locking while you hold the shutter release down. But remember - FEL may not be happening... That's why I asked if you are witnessing a pre-flash at any point. When FEL happens, you see a pre-flash occur, but no shutter opening happens, just a pre-flash that the camera took to determine flash power.

If you aren't seeing a pre-flash happen, the FEL isn't happening.

This is from my YN622C Guide, but is about Canon implementations:

Flash Exposure Lock (FEL)
• The camera must be in a creative mode.
• Live View mode must be disabled.
• Flash mode must be E-TTL.
• First focus on subject.
• Then press the camera’s