Head is swimming..do I understand?

Interesting discussion. Are you saying that there is a camera out there that has the CF4 set to 1 causing the * button to be reassigned as a autofocus button, but also retain it's FEL function too? How would you differentiate between the two functions on the one * button? (Now I know why I just leave the button assignment alone!) I think you might be referring to the 1DsMkII which MAY have separate FEL and Exposure lock buttons...but then...

Some camera's have ANOTHER button called the X button, which can be programmed to have the FEL function. In those camera's (10D) CF4 can set the * button as autofocus, and CF13 can set the X button as FEL.

In the 20D this is not possible and to use FEL, CF4 must be set to 0.

and the 1-series has its own dedicated FEL button.

Actually to go in to detail.... it has 2 FEL button. one on portrait orientation and one on landscape orientation.

The fact is, Wilt, that there is no digital EOS camera that retains FEL with the "*" button when the same button is reassigned for focusing via C.Fn-04. Yes, there are other cameras which have dedicated FEL buttons, like the 1D series cameras, and there are other cameras that allow you to reassign the FEL function to the "X" button, like the 10D, but there is no camera that does both FEL and focusing with the same "*" button and I think that was what our real discussion was about when you brought it up with the following:

It's a little tough here, it's one place the automated system fails. I tend to meter the exposure for the highlights in the background, and set the flash as fill. Sometimes the flash isn't powerful enough, use F32 if you have to to keep the shutter under 1/250th so you get the full power of the flash. I've occasionally has to switch to manual flash a 1/1 power (ie full) to get what I need out of it.

In my limited experience/testing, with my 350d I metered for the background and used the 580ex for fill. The only real issue I had was doing this in the evening caused some harsh shadows under the chin. Using the 580ex on camera, I'm not sure how this could be resolved. A reflector/additional off-camera flash/etc may have helped but with the setup as is, shadows may be unavoidable.

I'm not crazy about either of these shots as a whole but as far as exposure is concerned, I was quite pleased.

Daytime w/fill:

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Thanks all. Since I raised this topic yesterday- I went home and changed CF4 back to 1(I have a 20D). Did the same type of shot - metered the camera for the background, and then metered the flash off of the subject. Turned out quite nicely. NOw I just have to figure out how to focus (these camera's truly need another button) when I am metering off a distant background since by * button is now used by the flash....I guess manualy focusing is my only option..which is not bad...

If you have "*" set for FEL, then your AF focusing will go back to the shutter release button. AF will happen when you half-press the shutter button. You won't need to manually focus the lens unless that's what you want to do.

I don't know the answer, so I will throw it out there to see if some, such as PacAce, can answer....

I understand that you control the amount of light from the flash with the aperture. So shooting at a high f (small aperture) to stay under the flash sync would seem to defeat getting more strength from the flash. As Tim, I am sure, is aware of the ISO influence, I assume he was as low as possible in ISO, but that would also limit the increased strength of the flash.

However, we know that high speed flash does not have the strength of the sync flash.

So...the question....has anyone, for a given flash...say a 580EX, measured the trade offs of increased f-stop with sync flash vs faster shutter with high speed sync? At different ISOs?

As I said, I don't know the answer.

John

If I understand your question correctly, when the flash is in HSS mode, it is basically operating in "continuous lighting" mode for the duration of the shutter being open. So, that being the case, since the output from the flash in HSS mode is constant, you will be losing one stop of light for every stop increase in shutter speed. That makes sense because that's exactly what happens when with ambient lighting. The loss between using the flash in normal mode and the HSS mode at the lowest HSS shutter speed (i.e. 1/320) is about 1 1/2 stop (this is from either the 550EX or the 580EX manual, I forget which one I was looking at).

PacAce wrote:
If you have "*" set for FEL, then your AF focusing will go back to the shutter release button. AF will happen when you half-press the shutter button. You won't need to manually focus the lens unless that's what you want to do.

Right- but then I will be focusing on what I am metering- correct? Assuming I want the subject in the middle of the scene..

That depends on what modes you are using for the shot.

If you have the camera set to Manual mode, then you can set the exposure for the ambient light manually, then position the camera to FEL the subject and then half-press the shutter to focus lock on the subject, recompose (if necessary) and then take the shot.

If you're using one of the other creative modes with metering set to evaluative and in AF OneShot mode, then, yes, you will need to focus manually.

But if you're not using evaluative or OneShot mode, then it really doesn't matter because you won't be able to lock in the ambient light exposure anyway so you might as well use the shutter button half-pressed to focus in on the subject.

OK...I think I understand that.

So what is better? Decrease the aperture to keep sync flash or use HS flash? Is there a "cross over point" or is one always better than the other?

Or am I just totally confused thinking that a smaller aperture also lowers the sync flash effects on a per stop basis?

John

I realize this is flash forum, and I love to use flash much of the time for fill in daylight. But, sometimes, if time permits I like to use a reflector. This shot is as you described. 1pm bright daylight under a tree, using a 42" white reflector. 5D with 70-200 f2.8IS only PP was to sharpen and size for web.

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OK....I had someone work out the logic and math for me...and it seems correct.

Without going all through it, keeping at max. sync flash by increasing aperture will yield ~2 stops stronger flash vs. using high speed flash. This is based on equivalent metering for ambient.

Tim....why did I ever doubt you...???

John

BTW...the above assumes that you require the maximum output from the flash that you can possibly get. In most cases, you will require significantly less than full 1/1 power, which then makes high sppeed flash an attractive alternative.