Focusing problem with flash

eirefoto · Apr 16, 2016

Friends, I have a problem combining autofocus and on-camera flash. To some of you, this will sound simple but I have never tried any other setting apart from ETTL on my Canon 580EX II. I use a 5D III and a 7D but the problem is the same and this is it:

In a group shot (e.g. three rows of people, maybe 7 in each row) only the front row is in focus (obviously I choose a face in the front row for my focus point). The second and third rows are quite a bit out of focus. I could of course choose a face in the second row but . . .

Rather than setting everything on Auto, how can I get a deeper depth of field in my group shots - in other words, what settings should I use so that all three rows will be sharp?

I know it sounds basic but I'm afraid I just don't know. I find the 580EX II manual confusing. I would appreciate any help. Thanks.

eirefoto · Apr 21, 2016

Thank you for your comments. Yes, it does look as if the flash is not powerful enough. I have two 580EX II lights - and they cost me enough! They're dedicated to the EOS system so what would you all recommend?

LordKOTL · Apr 21, 2016

eirefoto said:
Thank you for your comments. Yes, it does look as if the flash is not powerful enough. I have two 580EX II lights - and they cost me enough! They're dedicated to the EOS system so what would you all recommend?

I'm not too familiar with the Canon system, but here's something I read from A quick Google search for the guide number on your flash:

An additional significant reason to use an external flash over a built-in flash is the amount of lighting output the external flash can provide. For example, the EOS Rebel XT/350D DSLR's built-in flash effective range (Guide Number) is 42' (13m) vs. up to 190' (58 m)(ISO 100 at 105mm) for the Canon Speedlite 580EX II Flash (same as the 580EX). Wider lenses will have a shorter effective distance, for example ... The Canon EF 50mm f/1.4 USM Lens has a range of approximately 98.4' (30m) with the 580EX II.

So, if I'm reading that right, your flashes should throw about 190 feet (58 meters) when using ISO-100 sensor sensitivity (or film) with a 105mm lens. If you drop to a 50mm the range drops to 98.4 feet (30 meters). I'm going to go out on a limb and assume wide-open apertures (someone with more knowledge of guide numbers, please correct me if I am giving bad info).

My guess on the matter is that your lens is very wide-angle with respect to the flash, and that since you're trying to bounce the flash off of a relatively high ceiling per your post, it's just not throwing as powerful as it should.

With my Nikon SB-500 i-TTL/D750, I can have the flash compensate +/- a couple stops, I'm willing to bet dollars to donuts your Canon system can do the same (I just don't know how--be it on the body or on the flash). I think that if you tell the flash to fire at a +1.0 give-or-take, the pictures should come out better. Just guessing that approx. half the mm = approx. half the distance of the flash throw, if the ceilings are less than 25' high your flash should have the power to bounce (and please correct me if I'm wrong on that). You might still get some vignetting because of the wide-angle of the lens but if you have the flash "overexpose" it should compensate for the brightness and help with the sharpness.

The only other suggestions I have would be:

Bounce card on the flash with the flash raised to 90deg.
Diffuser on the flash and pointed at the group.

I hope this helps and I apologize if any info I gave was bad.

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Focusing problem with flash

eirefoto

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eirefoto

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LordKOTL

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