Fill Flash - Depth of Field vs. Max Sync Speed (20D)

[dan magnus]

I was shooting an egagement session at the local botanical gardens

around 11am (full overhead sun). In shaded areas where I was not

concerned with eye socket shadows, I shot in Manual mode with my F4

lenses (17-40 & 70-200) opened up all the way for that great

background blur (sometimes AV mode with aperture set to F4). Even

in the shade at F4 I was having to use extremely fast shutter speeds

for proper exposure.

 

However, it seems that as soon as I turned on my flash (580ex

attached to stroboframe pro-T) to try and use as fill flash, my

shutter speed started to blink...I believe because it was over the

max sync speed (250). I figured the only thing I could do was stop

down the lens a lot to get the shutter speed at 250 or lower...but

then there goes my shallow depth of field and my great background

blur.

 

My experience with flash is somewhat limited, but shooting in Manual

mode I've been wanting to properly expose the scene and let flash do

it's own thing (+/- compensation when needed). But in this case, I

couldn't get the depth of field required AND exceed the flash sync.

Can you please advise me on what I might have been doing

incorrectly, or a better way to achieve this in the future?

Thanks.

[gaius1]

This probably isn't what you want to hear, but that kind of problem is best solved using reflectors and no flash at all.

[melisa]

If you want to use fill flash outside and use a wider aperture that results in higher shutter speeds, you'll need to incorperate HSS...High Speed Sync. Look in your manual for the 580 and it should tell you how to use flash at speeds over your sync.

[Ed_Ingold]

You need to "slow" the camera down so that the shutter speed for ambient light is under 1/250 second at f/4. The TTL flash will take care of the fill exposure level.

 

The simplest way is by reducing the ISO speed. If this is not enough, us a neutral density filter. These are commonly availble in 2-stop or 3-stop strengths, or even higher as needed. Cheap ND filters tend to have a color cast, so look toward the better filters like B+K, Heliopan or Hoya.

[micheleberti]

U need an high speed synch. Read the manual to discover the way to set it on the 580ex.

[cliff_henry]

Dan,

 

Melisa gets the prize for best answer!

 

Follow her advise and you will have no more problems.

 

Cliff

[cliff_henry]

Oops!

 

Should be *advice*.

[dan magnus]

Thanks for all the quick replies! Why didn't I think of High Speed Sync?! I'll certainly re-check the 580 manual for the way to set this up.

 

Follow up question...is there any "rule" as to how much flash to use (ie. +/- fec) or is it just trial and error? Also, should the effect of fill flash be noticeable in the historgram?

[melisa]

Thanks, Cliff. ;-)

 

In your flash manual, you should also find that the Canon flashes are programmed with fill-flash reduction. What this means is, starting at a metered reading of about EV10, the flash automatically starts cutting back it's power from .5 to 1.5 stops to give a more natural flash appearance. Now, the 580 is supposed to be improved from the funky metering of the 550ex, but you may find you want to boost/reduce the flash by using the +/- options on the flash. Or, you may want to override the entire fill-flash reduction system, by reading your camera manual, and turn off the function that runs the program, so you can do your own reduction. Outside, it's good fill-flash practice to reduce the flash anywhere from -1 to -2, depending on your style/preference.

[freddyv]

Drop your ISO or pop on a nuetral density filter.

<p>

Fred Voetsch

<br>

<A HREF="http://www.acclaimimages.com/">Acclaim Images</A>

[johnmarkpainter]

High Speed Sync is likely to bum you out. Low ASA speeds and ND Filters or the

suggestion of Reflectors/Shade and no Flash are good things to know as well.

 

jmp