FLASH - Maximising DOF whilst maintaining max sync speed

bl0at3r

bl0at3r

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Alan
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Hi, A true case of all the gear no idea I think :thinking:

I have a 7D, which has a max sync speed of 1/250. I also have a Speedlite 580EXII stuck on the top.

I have been happily snapping away, bouncing the light off the ceiling, walls etc and using a stofen where necessary.

I am having trouble getting all the faces for a group of people sharp (where they are not all the same distance away from the camera) - seems the camera is selecting a large aperture so the dof is very shallow. I have also never managed to achieve the max sync speed of 1/250 either - seems to favour 1/60.

These examples are from my GF1 - but it is the same issue - camera selects largest aperture.

P1010186.JPG

P1010187.JPG


Ideally I would want both faces in focus and I'm not sure what I'm doing wrong :bonk:

I want to take a photo with a small aperture to maximise the dof whilst achieving the max sync speed to freeze the action/movement.

Thanks
 
Alan, there are several "issues" here....

1. If you are posing people like this, why not simply position them so their faces are on the same plane, parallel to the camera sensor?

2. If you want to control DOF then you should be selecting the aperture, not the camera. Shoot in either Av or Manual mode.

3. The camera is picking these settings because the ambient light is very low and the camera is trying to drag in some ambient light first, before topping off with flash. For this scene you are at only 100 ISO. Why? If you want to pull in some ambient light then increase the ISO. That will allow you to increase DOF, or your shutter speed, or both.

4. For this image there is little point chasing the ambient light. You may as well do it all with bounced flash. With flash as your only significant light source you can stop down to f/8 and keep the shutter speed at 1/250 (not that you need to, but nor do you need a slower speed either). The flash will supply whatever power is required to illuminate the whole scene. Even at a shutter speed of 1/30, with flash as your only significant light source you would not see blur/shake at f/8 and 100 ISO, because the burst of light from the flash is very fast, and when that has gone there will be insufficient ambient light available to make a visible blur.

Do you understand that when you shoot with flash you are combining two exposures? - one for the ambient light and another for the flash. You can mix and match them as you like by adjusting various exposure parameters, but you need to take control of the camera settings if you want to be in control of the outcome of the image. even if you let the camera do some of the work you might need to help it along, by choosing an ISO that is better matched to what you want to achieve.

For this shot try 1/250, f/8, 200 ISO and BOUNCE the 580EX off the wall/ceiling behind you. You may need to adjust FEC till your happy with the result (try +1 to begin with) and then tune the settings from there. I don't know how big the room is, but if the flash runs out of puff then increase ISO to 400. Please don't use direct flash as you have done in the examples above. Look at the hotspots on their skin and those horrible flash shadows on the wall behind them. If you can get the further from the wall, and BOUNCE, that will help.
 
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Thanks guys for the suggestions and advice, much appreciated.

The 2 shots above were taken with the GF1 and built in flash rather than the 7D & 580 and were just an example.

I usually bounce the flash and use a stofen if necessary

I will have a play with the manual settings suggested on the 7d and let you knowhow I get on.

Thanks again :thumbs:
 
If you want to really know how EOS flash works then take a look here.

It is in 3 parts and does get a bit heavy going in places. Part II is where it describes how it sets exposure in each of the modes (P, Av, Tv & M) but it is worth skimming through the whole article.
 
Alan, I just tried it out for you, with a quick self portrait, curtains drawn to make the room dark. Without flash the image was completely black and there was nothing that could be pulled out at all with the most aggressive exposure boost in Lightroom. i.e. ambient light did not influence the picture at all. Everything you see below was lit by flash alone.

Here's how the bounced flash (behind the camera, up and at an angle to the left of camera) version looks at 1/200 (my max sync speed), f/8, 200 ISO and FEC at +1, no edits....

20100803_195935_4852_LR.jpg


If f/8 is not enough then there would be no problem to increase aperture to f/11 and maybe kick up the ISO to 400.
 
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Wow thanks Tim
Looks good to me and will certainly be experimenting myself

Going to my sisters wedding reception on saturday with the 7d & 580 (not as an official tog before all the pros start groaning :lol:) so am looking forward to it even more now :thumbs:
 
I recommend you take a look at this thread - http://www.talkphotography.co.uk/forums/showthread.php?t=242873. The technique in a large room will be a bit different, as one little flash won't do everything on its own so it'll need some help with a brighter aperture, higher ISO and slower shutter speed.

Here's an example from a wedding last year, taken at 1/60, f/3.5, 3200 ISO and with the flash bounced with a Stofen at +2/3 FEC. No edits except WB. I needed that exposure in order to pull in some ambient light for the background. Without that the background would have been jet black and the image would have looked pretty poor.

20090418_203745_6834_LR.jpg
 
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Great advice from Tim.

However, the problem with your first pic is that you have used the auto Portrait mode which deliberately selects a low f/number in order to blur the background, f/1.7 in this case, which is very low indeed. This is sometimes desirable for portraits, but obviously not always.

In a nutshell, you need to understand a little more about what your camera is doing, and how to control it better yourself. There is nothing difficult about getting those two people sharp. Nothing more than setting a higher f/number in aperture priority or manual, as Tim says. I have always thought those scene modes were useless, and in this case, worse than useless as they've given you the opposite of what you want.

Bounce flash, flash ambient balance, using a Stofen etc are different subjects.
 
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