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Old May 20, 2008, 11:57 AM   #1
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I recently had to resort to using the 550 flash with my Canon 40D for some indoor event photos and am having problems getting good exposures.

I thought with TTL the problems of over exposure due to closeness of the subject would be compensated for by the camera but that is obviously not the case.
Underexposed shots usually are the result of the distance to the subject is great and the ambient light is insufficient.

Overexposed shots are very common even though I expected the camera to compensate for this condition within a reasonable range.

I guess I don't really understand how to use the flash in the various modes to achieve a reasonable picture...not withstanding the bothersome aspects of harsh lighting, overblown areas, poor white balance. In some situations bouncing the flash of a ceiling helps but that is not always an option.

In the P mode there is a long delay (busy indication) in activating the shutter as the camera tries to figure out the exposure and even then the result is generally bad. In the other modes exposure seems a crapshoot and is typically poor. The long delay is really a pain.

Would using strobe lighting be a better option than the flash?

Can anyone suggest a tutorial or give me some guidance that would help me improve indoor shots using the 550 flash. ie How to set the shutter speed/aperture for optimum results or how to use manual settings to produce better results.

Thanks
Jerry
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Old May 20, 2008, 12:24 PM   #2
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I don't know much about the Canon flash system. So, perhaps NHL or someone else will chime in.

But, it's my understanding that the Canon System is going to let the flash provide most of the light in P mode; and with other camera modes like Aperture Priority or Manual Exposure, it's going to expose for ambient light, letting the flash provide fill.

So, if you have a lot of ambient light contributing, that could cause some issues like White Balance problems when the flash is not the primary light source (since the temperature of the light is going to be different). The use of colored filters would probably help that part out (for example, orange for incandescent so that the temperature of the flash light more closely matches the ambient light).

Using manual exposure gives you a bit more control with most systems. That way, you can dial in the amount of ambient light desired using the meter and let the camera determine how much flash to use for fill. For example, if you wanted to isolate your subject more from the background using flash, you could use a smaller aperture (higher f/stop number) and/or lower ISO speed and/or faster shutter speed so that ambient light is contributing less to the exposure (so that your subject is mostly being illuminated by the flash with a darker background).

Or, you could do the opposite (use a higher ISO speed and/or slower shutter speed and/or wider aperture) so that more ambient light is contributing, giving you a brighter background (keeping White Balance issues in mind).

As for your exposure problems, what metering are you using? Most metering systems are going to weight your focus point more (that's what the camera is probably looking at when judging the amount of light from the preflash to determine the length of the main flash burst needed). So, if your subject is darker, that could lead to overexposed images with some cameras (and the opposite if shooting a lighter subject). I tend to use center weighted metering more with cameras I use (which tends to be more predictable compared to matrix or spot with most cameras).

As for your underexposed images, I'd make sure you're within the rated flash range for the aperture and ISO speed you're using. Your maximum flash distance at ISO 100 is going to be the GN divided by your aperture setting. Then, each time you double the ISO speed, flash range increases by 1.4x. That assumes a direct versus bounced flash, and the GN will vary by focal length (you won't get as far at a wider angle setting with the flash zoom head). Also, if you exceed the camera's x-sync speed, you will lower your maximum flash range significantly, because the flash will need to use high speed sync (FP mode), pulsing the light as the shutter curtains travel across the frame.

Hopefully, someone more familiar with the Canon flash system will chime in with tips.

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Old May 20, 2008, 1:45 PM   #3
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Thanks Jim That is very helpful... to answer your question, in most cases I am use center weighted metering.

To avoid the harsh lighting effect of the flash do you think it would it make sense to use more ambient lighting (higher ISO, slower shutter speed/wider aperture) and have the flash provide flash fill?

Jerry
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Old May 20, 2008, 2:11 PM   #4
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Well, I don't claim to be a flash expert, and I prefer to use ambient only when I can get away with it. But, it would depend on the conditions with me. I'm using cheap Sunpaks for a flash system right now with manual exposure, and tend to use both approaches (more ambient light in some cases, less in others), depending on the room size, lighting, and more), taking a few test shots to tweak my settings.

One downside of dialing in more ambient light is that the flash won't be able to freeze the action when you have a moving subject. With flash as the dominant light source, you can easily freeze action with one in dimmer conditions. That's because the flash burst is very short (usually around 1/1000 second or faster with most flashes). So, if ambient light isn't contributing as much to the exposure (i.e., your subject would be dark without it), then the flash can freeze it for you (since the subject is only going to be properly exposed during the short flash burst).

If you dial in a lot of ambient light, then you can get some blur from subject movement if you're not careful with shutter speeds (which has no impact on the amount of light seen from the flash, as long as you're withing the x-sync speed limits).

IOW, it depends. ;-)

As for the harsh lighting with flash, bounce it (provided the ceiling height/color lends itself well to that and you don't run out of flash power). You may get a hot spot or two if it's too powerful (even bouncing). For example, white napkins on a table. But, most of the time, you'll get fairly even lighting that way using a flash as the primary source.

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Old May 20, 2008, 2:19 PM   #5
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You may also want to get a diffuser if you don't use one to help diffuse the light some. Or, you can even make your own. Many are designed to let some of the light go up, and some of it forward.

I'm been thinking about getting one of the Lambency "Inverted Dome" type diffusers that come with an Orange dome for tungsten lighting. They're very inexpensive if you go with a "knock off" (versus the Gary Fong name brand versions). You can see some examples of diffusers on this page (and this is a reputable hong kong based vendor):

http://www.gadgetinfinity.com/home.php?cat=273

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Old May 20, 2008, 2:23 PM   #6
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NHL hasn't been around much, so you might have to wait a few days.

In the meantime though it would help if you could post a few shots with exif data so we can get an idea what the problem might be.

In general unless you really know what you are doing you want to stay away from Aperture and Shutter priority modes with flash, stick to Manual and Program.

Use matrix metering not-centre weighted to get a good exposure on the full scene with Program mode, and let the flash fill in. Alternatively use spot metering and manual mode, take a few test shots (digital is free right) so that you can get a good feel for what you will be getting without the flash in manual.

THEN add flash and adjust for the part of the scene you are interested in.

I generally use flash in reasonably small environments that are capably of taking bounce and lighting the whole room (with a stofen diffuser attached). Also experiment with FEC settings; I find that I get nice skin tones with about minus half to minus one FEC dialled in , Program mode and matrix metering.


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Old May 20, 2008, 2:49 PM   #7
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Thanks P
I am not familiar with matrix metering--is that the same as evaluative metering in the canon 40D?
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Old May 20, 2008, 4:04 PM   #8
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Thanks again Jim
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Old May 20, 2008, 5:47 PM   #9
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Matrix is sometimes called evaluative, and sometimes called mult-segment.

It's behavior tends to be camera dependent, and with most cameras, it's not quite as predicatable as center weighted from my experience. Basically, proprietary algorithms are trying to determine the scene type and sometimes brighter or darker areas in a scene somewhere can easily fool many of them, giving inconsistent results.

With some dSLR models, the trend seems to be more weighting of the focus point than previous matrix systems. I will say that it appears to be much improved on my Sony A700, as compared to my older KM 5D. But, I think I'll probably stick to Center Weighted for most things. YMMV using different cameras, and it sounds like peripatetic thinks Matrix is a better way to go with your Canon.

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Old May 20, 2008, 10:34 PM   #10
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coachjerry wrote:
Quote:
... How to set the shutter speed/aperture for optimum results or how to use manual settings to produce better results.
I think you got it...
-> The best way to use the Canon flash as peripatetic has pointed out earlier is to put the camera on manual (i.e. you get to pick both the shutter and aperture) and don't worry the E-TTL flash will fill the rest for you automatically

IMO most of the under/overexposure could be subject related as the camera's metering is quite sesnsitive to the subject content as darker subject will push toward overexposure and brighter subject will make darker...
-> To keep the exposure constant I normally use the FEL button to lock the exposure on people face (or neutral gray area) for example before recomposing
Also when you use FEL the camera is programmed to meter only the central area instead of the camera's normal evaluative metering (i.e. more weighting to the center of the viewfinder)

This is probably the most comprehensive write up on E-TTL: http://photonotes.org/articles/eos-flash/#ettl
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