How do I get more DOF with flash?

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Duncan.F

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Duncan
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Hi,
I do a lot of flash photography but am sometimes disappointed with the dark background behind subjects. Now a lot of this is candids so i don't get time to faf around and tend to leave on P and hope for the best.....Maybe not a good plan!
I have upgraded from a 380ex to a Canon 580ex and have been doing some reading on the subject. What it seems to tell me is that to increase DOF I need to go into AV mode and use say 4 or 5.6, but when I do this the shutter time increases to something silly and way too slow. If try to alter in TV mode then the camera tells me that the apeture is wrong. Yet in P mode it will seeming work quite well at similar settings so am I doing something wrong....? Using a Canon 40D now!

Cheers,

Dunc
 
The way i understand it is to slow the shutter speed. Slow-sync. That way the shutter captures more of the light.
I am just a beginner when it comes to flash though...:)


Kev.
 
The aperture controls how much flash affects the subject and the shutter speed controls the amount of ambient light. You need to balance the two to get the result you want. Try shooting on Aperture priority or Shutter priority to give you more control.

I'm not sure you really mean Depth of Field either - I think you want the flash to cover a 'deeper' area from the camera? You could also try bouncing the flash.
 
If you want more DOF in the pics then switch camera to manual (or AV) and stop down more, bearing in mind your flash distance will be reduced a well.

The way I do it inside large rooms is to have the camera approx F11, shutter approx 1/8th and put the flash on manual output. Do a couple of test shots and then fire away (I found Canon ETTL tends to underexpose)

The slow shutter speed should record some of the ambient light in the background, but best to play around with the shutter speed to get the results you are looking for, slower shutter speed=more ambient light, but be careful of camera shake.
 
The dark background is to do with the ratio in distance between the flash to subject and the flash to background. If you want more flash light on the background using only one flash then you need to move the light further from the subject or move the subject closer to the background.

If you want ambient light on the background then leave the shutter open for longer.
 
Hi,
Thanks for the responses! To explain a little more, I photograph say 2 people in a dark room but with others behind. Those behind are in the dark and it ruins the shot. What I would like is to be able to capture the group. I appreciate there are limits about how much light a flash can chuck out.
When I tried to alter in AV mode to say 4.5 the shutter speed went up to 10 seconds or more, even with ISO at 400 or 800.

Cheers,

Dunc
 
Read this. First thing I would do in your shoes is get comfortable in using your camera and flash in manual, some systems are better than others but you can't completely trust the camera to get every shot right so sometimes you need to take control.

It sounds like you camera is exposing for the people in the foreground and really unless you move the people or the light source you won't get the people in the background illuminated the same (unless you start adding a second flash).

Why not post an example for us to see.
 
Hi,
Here are a couple of samples with the darker background. Straight from camera.

darkish1.jpg




darkish2.jpg




These are not the worst and most are considerably better!

Cheers,

Dunc
 
They're not as bad as I was expecting. That's quite a big space for one flash to ligt evenly, did the link I posted make any sense to you and explain why the furthest ones are darker then the near ones? I reckon if you'd taken a few steps back and zoom back in to frame them the light coverage would have been a little more even (but probably not completely even.
 
Hi Kev,
Read the Strobist article and yes its really useful and makes sense. I will try that little exercise at the end but the inverse law now makes sense in terms of what I felt I was doing wrong. Thanks!

Dunc
 
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