Aperture Priority at f/1.4 with Flash: Shutter too slow.

[bellavance]

I like using Aperture Priority on my 10D with my 50/1.4 lens and

420EX flash for party portaits, because of shallow depth of field

when lens is set to f/1.4.

 

Problem - Aperture Priority automatically causes camera to use very

slow shutter speeds to expose for background while the flash exposes

for the foreground. I find myself using ISO 1600 and even 3200 to

get reasonable shutter speeds because of the low ambient light.

 

Question 1 - Is there a way to use higher shutter speeds while

shooting at f/1.4 other than using manual mode?

 

Question 2 - If I use manual mode, and thus choose a reasonable

shutter speed and f/1.4, will the flash control its power to get a

good exposure of my subject?

 

Thanks

 

Pierre

[daniel_ong]

Pierre,

 

Set C.Fn-03 (custom function 3) from 0 to 1 and your 10D will automatically set the shutter speed to 1/200 sec.

[charles barcellona www.bl]

As you can see, the camera always tries to expose for the ambient light, which will end up as the light of the background, since the shoe mounted flash will provide lighting objects that are closer.

 

You "could" use the CF and set the speed at 1/200. Of course than you'd get dramatically underexposed backgrounds.

 

I think there's a better way, by using M as you suggested.

 

Meter the scene in M mode, and set the shutter speed for a fairly long, but not overly long setting. With a 50mm lens on the 10D, I think I'd go as long as 1/15 sec. if I needed to, in order to get the exposure ok for the background. If you dont need to use that long of an exposure - you can always close the lens a bit for more DOF. If you need more exposure - longer shutter speeds - you can possible do it handheld if you're very careful, because its going to be mostly out of focus anyway at f/1.4. If not... then just go with as long as you feel comfy with handholding, allowing a bit of blur (its ok since the main close subject will be frozen by the flash). If you end up underexosing the background at 1/15 sec (or whatever speed) its still better than going with 1/200 all the time, and getting black backgrounds. Experiment a but, you'll get some interesting stuff.

[dennis_pereira]

Your manual settings will affect the ambient light exposure, the flash will properly expose for the subject in focus. Pick a shutter speed up to 1/200.

[jim_larson1]

I shoot most of my flash shots in "M" for this very reason. The E-TTL system will take care of flash exposure.

[jbq]

-There's a custom function to force the shutter speed to 1/200s in that case. I personally use manual mode and a shutter speed of 1/90s,

typically at f/5.6 ISO 400 though I've also used other settings.

 

-Yes, in manual mode E-TTL will still give you a good exposure for the subject in focus.

[mark u]

There's a simpler answer: use P mode. This will set a shutter speed that avoids camera shake. If the light is dark enough that you were using high ISO to boost the shutter speed at f/1.4, then it will also select f/1.4 at similar or lower ISO settings. The flash will expose for the subject (the area round the focus point). Of course,you can also set this up in M mode. You may find that flash exposure is a bit sensitive to what lies under the focus point. You might be able to get round that by switching the lens to manual focus which causes flash exposure to be based on all 35 metering segments - but then you're left trying to focus manually in dim light via a small viewfinder image when shooting wide open (i.e. when focus is critical).

[bellavance]

Thanks to all for this information. I will try Manual Mode today. It looks promising.

 

Since I will see the results right away on the 10D's screen, I can adjust ISO and shutter speed for the background exposure I prefer.

 

Thanks again.

 

Pierre

[jim_larson1]

Also, in "M" mode, the exposure indicator will give you a hint at how underexposed the <i>ambient exposure</i> would be for the shutter, aperture, and ISO you select.<P>Can't emphasize enough how important it is to watch where the focus point is when you take flash photos. Focus-Recompose is evil if you don't use Flash exposure lock.

[bellavance]

You said: "Focus-Recompose is evil if you don't use Flash exposure lock."

 

Isn't flash exposure automatically locked when you focus on your subject?

 

Pierre

[jbq]

Pierre: Only regular exposure is locked when you focus-recompose. Finding flash exposure requires to fire the flash, and you wouldn't want it to fire each time you focus, would you?

[bellavance]

I thought that the flash determined some sort of exposure when the camera was focused. Probably only the distance, then.

 

For flash exposure lock, you have to press the * button?

 

I think I should read the manual one more time... ;-))

 

Pierre

[jbq]

Pierre: I may be totally wrong here, but I recall reading that Nikon had a patent on the idea to transmit distance information from the lens to the flash in order to determine flash exposure, so that Canon can't do the same.

[jim_larson1]

There are two major factors required for correct flash exposure: <list><LI>distance from flash to camera<LI>reflective properties of the subject,</list>

<p>

While the focus system can figure out the first item, it has no clue regarding the second item. Normal E-TTL operation acutally involves a preflash to determine flash exposure. Using the information from the preflash, the camera then opens the shutter and fires the required flash power.

<P>

Where things get tricky is the simple fact that the camera attempts to illuminate <i>the subject</i> and not the <i>entire scene</i>. This is important when you have, let's say, a portrait at night in a park. No way the flash can expose the entire scene.

<p>

Now, how does the camera know where the subject is? Simple. It's under the focus point!. Opps, you say you moved the camera between when you focused and when you hit the shutter? Now, how is the camera supposed to know that? The Canon method is simple: If you know you are recomposing the scene, you have to tell the camera what it is supposed to meter for. That is Flash Exposure Lock. When you do Flash exposure lock, the camera acutally fires a preflash to determine the flash power that will be used in the final shot.

<p>

The other time FEL is important is if you want to focus on something that will mess up a flash meter (black suit, a glittery dress, a white dress). In these cases, the best bet is to FEL on a subjects face, set focus, then shoot.

[howard_hecht]

This issue has always perplexed me as well, and as a result I often use Program mode (or in rare cases, Manual mode). It plagued me this weekend during a shoot so I figured I'd do a search and came across this article. Thanks to all of those who contributed.

 

Now that I understand it a bit more, I'm even more dumbfounded by the decision that Canon made. Am I missing something, or would it not make more sense (in Aperture Priority mode) to have the camera choose the appropriate shutter speed to properly expose based on the metering mode you've chosen, and/or based on an area that you want to meter? That is, instead of what it seems to be doing which is choosing the shutter speed based on a full-frame meter instead of spot, center weighted, etc...

 

This is driving me crazy. Seems so simple that you'd be able to:

 

1. Set your desired metering mode for your metering measurements.

2. Choose your desired Aperture.

3. Meter on the "important" subject or area of the frame (if not the entire frame based on your mode).

4. If you're going to recompose, lock the metering value.

5. Release the shutter, with the camera exposing for the metered area, INSTEAD of the background...

 

I'm sure I'm missing something... what is it? Why can't Canon get this right? I would use A-priority mode far more often if it didn't always give me ridiculously long exposure times when all I want is a certain Aperture for a desired DoF!

[mark u]

Beware that some of the advice in this thread is very specific to the 10D body. Also be careful to distinguish between how the camera is set for ambient metericng, and for flash metering. In essence, flash metering **with a 10D** is spot metering at the focus point at the time that the pre-flash is emitted, and average metering if the lens is set to MF or if you are using * CF 4 to focus AND you are not pressing the * button when taking the shot. There is in principle nothing to stop you from choosing any ambient metering mode available - but that will only influence how the ambient exposure is measured. Other cameras behave differently.