How to use flash with av,tv

[gjones5252]

I have a question that has been plaguing me for quite some time. I have searches every where but apparently I am not typing in the right search terms.
Whenever I have a flash on either 5d2/3 and it is in av,tv mode I feel as though the camera is not compensating for the flash. IE instead of an appropriate exposure of 1/60 it will be at 1" as though I didn't even have a flash on there. I felt as though it did this on my 60d when I still had it. By my 5d2 didn't. I assumed it was like the ISO 400 thing and would be fixed on 5d3.
However after using the 600exrt and 5d3 tonight it seems much more likely user error.
Please can someone explain this and possible some other flash thing like why it goes to ISo 400 ??
Or tell me where to look or how to play and figure it out.
This forum is so useful to me in learning the functions of some of the more technical sides of cameras.

[DocMo]

I may be wrong, but it's my understanding that the camera metering system will meter only for ambient light, and will not change regardless of if you have a flash on it or not.

Things get complicated with the flash because you have an interplay of two different systems - the body meter for exposure and then the flash reading for power (the body measures both through e-ttl - evaluative through the lens). Starting out, I found it easier to go to manual on either the body or the flash so that I could figure out what the heck was going on. 

[pwp]

I use AV and flash all the time. You've got to know when and where to call in this combination but it could be anything from bright sun using HSS flash and a semi dark reception or venue location. There's little point in trying to read up on this, just DO IT. Your own experimentation will reveal far more to you in just a short space of time than any amount of drilling through the www.

Sometimes you can come up with brilliant effects, or just plain competent technically correct results.

People who are reluctant to experiment may have origins in the film days when experimentation could get expensive...it could cost you a dollar every time you pressed the shutter. Do what teenagers do instinctively...just try...fail....try something else...maybe fail...try something else etc etc. Fear of failure is a non-issue, nobody is watching and it doesn't cost you a penny. And it's FUN.

-PW

[vlad]

Ugh, I struggled with this a lot when I was first learning to use a flash.  What you're seeing is the intended design - in Av and Tv, the camera meters as if there was no flash at all.  The idea is that it meters for ambient light (i.e. as if there is no flash at all) and then the flash output is responsible for the exposure on whatever the flash is lighting.  The flash output is either set manually or via ETTL.

This threw me off because as a beginner, I would start with automatic settings, then turn to using manual ones one at a time as my comfort zone expanded.  With flash, however, it's way easier to just go with manual - camera AND flash.

Look at it this way, with camera in Av and flash in ETTL, a slight difference in the shot, say a bit more sky in the frame, will change the shutter speed, unexpectedly altering the ambient exposure.  And with ETTL, you're essentially telling your flash - go head - expose for what you think is right, I trust you!  With that number of variables, it can be hard to just get a sequence of shots exposed consistently, much less have a properly controlled lighting situation.

So my advice is, start with camera in M.  You can even use Av or Tv to first get the ambient exposure you want, then switch to M and dial those in.  As you get more comfortable, you won't need that step - just start in M, set the shutter or aperture that you want, and dial the other one until the meter lines up.  Now that your're in M, at least your ambient will stay the same and not be thrown off by metering.  You can leave the flash in ETTL and use FEC to dial it in, but I wouldn't recommend it - I always found myself spending more time chimping and tweaking the FEC than getting the shot I want.  So put the flash in M, take a few practice shots to find what it needs to be adjusted to, and voila - you have achieved a state of permanence.  If the conditions, the distance/angle of flash to subject, etc stay the same, your shots will remain consistent and not be at the whim of automatic processes that can't possibly guess what exactly you want your shot to look like.

When I'm bouncing the flash or using some kind of diffuser, I'll use ETTL more often - it makes more sense in this scenario since, if you're moving around, the characteristics of the bounced light can change, and ETTL does a pretty good job of figuring out a decent exposure.

Disclaimer - there are a lot of ways to shoot with flash.  My experience is based mostly on shooting people outside with off-camera flash.  I chased what I believed was the ETTL holy grail that would do it all for me, buying the fancy PocketWizards, etc, but it seems that the more proficient I get, the more manual I get with my flashes...

[m]

Use M to dial in your settings which can pretty much stay the same the entire shooting, depending on what you shoot.

Choose a time to stop motion or engage it (with rear curtain).
Pick a aperture that works for the situation, it's probably dark, but don't go too wide open.

I tend to use higher iso values (like 800) to reduce flash output, for less batteries and faster recycle times.
Yes that's high, but I'm often shooting in very dark situations.

The only downside is that it's still TTL.
So if the pitch black surroundings and the foreground lit by flash should add up to 18% grey, the foreground can be a bit overexposed.
In my situation, that's fine. It's not necessarily in yours.

[bycostello]

the camera is only trying to fill the shadows, so if dark, you won't get much flash...  use in P or M to get the results you expect...

[alexturton]

For speed lite photography I remember 1 rule:

Shutter speed controls ambient light
Aperture controls flash

If your ambient it too dark/light adjust the shutter. If your fill subject is too dark/light adjust the aperture.

The only exception is if you need to be at max aperture and your fill flash it too strong. Then dial down the fec a few stops.

[alexturton]

I would highly recommend this book.

http://www.amazon.co.uk/Speedliters-Handbook-Learning-Craft-Speedlites/dp/032171105X

[neuroanatomist]

You also asked about ISO 400 - the camera selects that in Auto ISO with a flash as a compromise.  Higher ISO means your flash power goes further, lower ISO means less noise.  If you manually set an ISO, you can set whatever you want.

[bycostello]

I would highly recommend this book.

http://www.amazon.co.uk/Speedliters-Handbook-Learning-Craft-Speedlites/dp/032171105X

+1

[filo64]

With the 5D Mark III, you can set "Flash sync. speed in Av mode" to be AUTO, 1/200 - 1/60 A or 1/200 (fixed). The details are on page 192 in the manual (both the pdf and the hardcopy, I believe).

[Rat]

Check out http://photonotes.org/articles/eos-flash/ - start your reading at Q7 in the FAQ. By the time you reach Flash Metering Principles, about three to five minutes later, you'll have some very useful info

[tcmatthews]

First I am not an expert and have been thinking of getting the speedliters handbook myself.  First you have not mentioned how you plan on using the flash, first curtain, second curtain or high speed sync.
Normally I just set it to M and make a couple of test shots and leave it there.  But sometime use it with Av mode. If you just want to use it for general snap shots or group photos you can force the default shutter speed as filo64 mentioned. 

With the 5D Mark III, you can set "Flash sync. speed in Av mode" to be AUTO, 1/200 - 1/60 A or 1/200 (fixed). The details are on page 192 in the manual (both the pdf and the hardcopy, I believe).

For TV in first and second curtain modes you will be limited by the max sync speed of the camera.  But i found it rarely sets the aperture to my liking which is the reason to use M.

You can use a flash to get effects in low light that are impossible otherwise.  On method is to use Av to expose the ambient background and the flash on second curtain to stop motion. This will give a sense of motion in the photo. 

High speed sync is a completely diffident beast I sometimes use it for fill flash.  But I am far from an expert and find my self shooting in the dark until I get the effect I want.