Problems with exposure when using flash.

[BEphoto]

Ever since ive had my camera ive pretty much shot in Av or Tv mode depending on the situation. I rarely use auto or program at all, and not a whole lot of full manual. Anyway, my question is this...

I was at the camera store today talking about my flash that i got a couple of weeks ago (580EX II speedlight) and i was telling him that i cant seem to get it right, blah blah blah...

He said he shoots pretty much everything with flash in Program mode, rather than Av. So i came home and played with it and the pics turn out very nice color-wise and exposure. I check what settings the camera chose, switched to Av and chose the same aperture setting assuming it would give me the same shutter speed that Program mode gave me. It didnt. It was exceptionally slower. I believe Program gave me something along the lines of f/4 @ 1/60 (sitting in my living room). I switch it to Av, put it on f/4 and i think it gave me like 0"3 or something similar. Either way, it was nowhere close to what program mode gave me when it produced a great exposure. when i take the picture in Av it comes out very yellowish and obviously blurry.

Im still a complete noob with my 580EX II and was wondering if maybe there is a setting that is different when i switch to Av that makes the exposure come out different.

Here is an example i literally took just now. Both shots sitting in the same spot, the only thing different was that i saw the aperture setting that Program mode gave me, stuck the camera in Av, set the same aperture and fired again. this is the results....

Program shot:

http://i49.photobucket.com/albums/f256/bradleygt/IMG_0016.jpg

.....and the settings the camera chose

Aperture: f/4.0
Shutter: 1/60
ISO: 800
Auto White Balance
no flash or exposure compensation
evaluative metering

Now for the Aperture Priority shot

http://i49.photobucket.com/albums/f256/bradleygt/IMG_0017.jpg

....and the settings the camera chose when i matched the Program mode's f/4.0 aperture

Aperture: f/4.0
Shutter: 1/4
ISO: 800
Auto White Balance
no flash or exposure compensation
evaluative metering


Same set of parameters for both shots.

What the heck is going on? Did i change something in-camera at some point that is making it do this? or maybe something related to the flash? Ive been shooting in Av for 3 years and now i feel like im starting from scratch again....

any help is greatly appreciated.

Brad

[Papa Carlo]

Set your camera to manual. Shutter speed 1/250, apperture to what is required by your desired depth of field. The flash will do the rest.

[BEphoto]

that actually seemed to work out pretty dang good. my camera wont let me go to 1/250, only 1/200, but whos counting. Thats pretty crazy though. Even the in-camera meter says its going to be underexposed but it turned out looking pretty much just like the program mode.

maybe ive been shooting in the wrong mode for the last 3 years.... bleh...

Thanks a lot!

[fullcity]

I have seen the exact same thing happen with indoor shots on my XSi and a 220 EX (haven't had a chance to upgrade yet). Av mode works great in daylight and indoors without flash but when flash is engaged, it all falls apart (chooses a slow shutter speed) -- so I'm also curious why that is.

Edit: just found this thread (http://photography-on-the.net/forum/showthread.php?t=600927), which explains why Av mode does not work so well with a flash.

[BEphoto]

I have seen the exact same thing happen with indoor shots on my XSi and a 220 EX (haven't had a chance to upgrade yet). Av mode works great in daylight and indoors without flash but when flash is engaged, it all falls apart (chooses a slow shutter speed) -- so I'm also curious why that is.

Do exactly what Carlo said above. works freakin great. i just went to a hallway with no lights on and shot manual at 1/200 and f/2.8 and got a great exposure.

From now on im staying in manual when using flash. Thanks again Carlo, you may have just made my photography career take a huge leap foward.

[MinhThien]

I know most people use Manual when shooting with the flash, but i found that on TV mode i get better result! Maybe is just me?

[fullcity]

I know most people use Manual when shooting with the flash, but i found that on TV mode i get better result! Maybe is just me?

Interesting, I just tried a couple of shots (of my kid), one with Manual 1/200s f/2.5 and one with Tv 1/200s (camera chose f/1.8 ). The Manual shot showed a blown highlight (white area on her shirt) in the LCD, whereas the Tv one was fine. If I knew what I was doing, I probably would have corrected the aperture in manual mode so as to not get any blown areas, but Tv is a foolproof way to get the shot. Both looked great though.

[w7cma]

Go to custom function settings 2 and set it to option 1 (fixed) you should be able to shoot on av mode just fine.

[BEphoto]

Go to custom function settings 2 and set it to option 1 (fixed) you should be able to shoot on av mode just fine.

in-camera or on the flash?

[fullcity]

Go to custom function settings 2 and set it to option 1 (fixed) you should be able to shoot on av mode just fine.

Custom function 2 = "Flash sync speed in Av mode" -- bingo! Thanks, works like a charm. But I can also see why one might not want want that as the default, for example if you have a background at night or in a dark setting that you don't necessarily want to be all black.

[coalcliff]

in-camera or on the flash?

Cfn 2 on the 580Ex11 controls the use of the modelling flash..
Cfn 2 on the 40D controls the noise reduction or highlight tone priority..

what is the OP shooting with?

[BEphoto]

ohh, i found it. mine was just custom function 3. good concept but im thinking ill just do the same thing in manual so i dont forget about that being on at some point where i dont need it and miss a shot.

Thanks again though!

[BEphoto]

what is the OP shooting with?

Rebel XT

[MinhThien]

Interesting, I just tried a couple of shots (of my kid), one with Manual 1/200s f/2.5 and one with Tv 1/200s (camera chose f/1.8 ). The Manual shot showed a blown highlight (white area on her shirt) in the LCD, whereas the Tv one was fine. If I knew what I was doing, I probably would have corrected the aperture in manual mode so as to not get any blown areas, but Tv is a foolproof way to get the shot. Both looked great though.

Try to bounce the flash under TV! You'll see!

[fullcity]

Try to bounce the flash under TV! You'll see!

I certainly will ... when I get around to upgrading my 220 EX! ;)

[gofer]

The results I see are exactly what I would expect to see given the settings you used. In 'P' mode the camera has recognised that a flash is attached, set the shutter speed accordingly and exposed the scene for a flash exposure. In 'Av' mode the camera still exposes for ambient light and simply uses the flash as fill light so the camera will set a shutter speed relative to the aperture you have selected and the ambient light available. Obviously from the images you've shown, the ambient light was much warmer than the flash and, as the camera is still trying to use ambient light as the main light source, the pictures look warmer. The 'Av' mode shot is also more blurred due to the lower shutter speed required for a correct ambient light exposure. Nothing is wrong here except your choice of mode. As others have said, better to use 'M' with the shutter speed set to the maximum sync speed, the aperture set to whatever you think is going to give you the required DoF and just bounce the flash. Providing the flash is set to ETTL and you're within the capabilities of the 580, everything will be fine.

[bohdank]

On camera, set flash synch speed = 200 (250 on 40D). go Av mode... enjoy.....

[JeffreyG]

In a nutshell, Av and Tv modes ignore the flash. So when you use these modes with flash they will still select setting to expose the ambient even when it is very dark. Thus the crazy slow shutter speed.

The other thing you need to understand is that the meter in M mode is telling you what the exposure will be based on ambient light. It has no idea what the flash will look like until the pre-flash fires. So most of the time when you are shooting in M mode with a flash you will be selecting aperture and shutter that has the needle off the left side of the scale.

The reason P mode works with flash is that it applies logic based on ambient. When it is fairly dim, P decides you mean to use the flash as main light and not fill so it starts to underexpose the ambient.

I recommend reading the stickies in this forum on how flash really works and then using it pretty much exclusively in M mode.