av mode blurry image

first time i am trying a flash .

camera is 7d. made the flash wireless (only ext.flash firing). in Av and Ettl mode.

when there is no much ambient light before I snap the pic. lcd obviously shows very slow shutter speed say 1/8 th of a second.

I press the shutter and take the picture imagining the ext.flash will take care of pushing my shutter speed up. But I am getting blurry images all the time.

am i doing some thing wrong???

thanks in advance for the clarification.

cheers

sanil

In AV mode the camera is still setting the exposure for ambient light. It will set the shutter speed to get that exposure, thus the 1/8 sec shutter speed. You might try TV or manual to control the shutter speed.

Yes your shutter speed is too slow. In photography the aperture controls exposure for flash, and the shutter speed controls the exposure for ambient light. Set the camera to manual and the aperture for flash to shoot at your desired DOF. The shutter speed to one that will approximate your focal length not to exceed 1/250 sec.

Yeah, in Av mode the camera uses ambient for the exposure and the flash is just used for fill light. If you want the flash to be the primary light source you need to get out of Av and ETTL.

LBaldwin wrote in post #12972281
Yes your shutter speed is too slow. In photography the aperture controls exposure for flash, and the shutter speed controls the exposure for ambient light. Set the camera to manual and the aperture for flash to shoot at your desired DOF. The shutter speed to one that will approximate your focal length not to exceed 1/250 sec.

sorry i didnt understand.

i will set the camera into manual mode and flash into ettl mode.

for dof lets say i will keep aperture at 1.4 then if i set the shutter speed closer to 1/250 if its showing underexposed is that ok. you mean will the flash takes care of the rest.

anil

sanil wrote in post #12972245
I press the shutter and take the picture imagining the ext.flash will take care of pushing my shutter speed up. ...
sanil

Part of the problem is that this is not what happens. The camera will not change your shutter speed at the time of shooting; whatever setting you see when you half-press the shutter button is the setting that the image will be taken with. So, in your case, the shots are being taken at 1/8s shutter speed; you either need to shoot in a different mode that will allow you to specify the necessary shutter speed, or to dial in a stop or two of Exposure Compensation to override the camera's decision.

Snydremark wrote in post #12972438
Part of the problem is that this is not what happens. The camera will not change your shutter speed at the time of shooting; whatever setting you see when you half-press the shutter button is the setting that the image will be taken with. So, in your case, the shots are being taken at 1/8s shutter speed; you either need to shoot in a different mode that will allow you to specify the necessary shutter speed, or to dial in a stop or two of Exposure Compensation to override the camera's decision.

So if you were to shoot a scene which is 1/60 @ f/4 (max aperture) and moved to Tv and bumped the shutter to 1/125 the E-TTL would power up the flash by half a stop, correct?

tman2782 wrote in post #12972938
So if you were to shoot a scene which is 1/60 @ f/4 (max aperture) and moved to Tv and bumped the shutter to 1/125 the E-TTL would power up the flash by half a stop, correct?

No. In Tv mode if you were to change to 1/125, the aperture would stay at f/4 (because it is max) but the camera flash would stay the same. ETTL preflash does not care how long the shutter is open. It only cares about the aperture. (and distance, ISO, reflectivity, etc)

Flash duration can range from 1/1000 at full power to as little as 1/10,000 at lower power. The flight from the flash will be the same no matter what shutter speed is used.

That can't be exactly right. He's underexposing* his subject by one stop so E-TTL will make up for that with flash output. That's its job.

For the same flash output, the shutter speed doesn't affect flash exposure but that's not really the issue here, is it? This is ETTL, not constant flash output.

* Edit: underexposing in ambient

Most of the time flash is used in a dark environment with little ambient light. The foreground will be illuminated by the flash and the background will be ambient light.

In most cases it is objects in the foreground that is the subject, and which is lighted by the flash. That is what will determine the power of the flash. A change in the ambient exposure will have little or no effect on the power required to illuminate the foreground.

If you are shooting fill-flash in bright daylight, then the flash power might be more effected by a change in the ambient lighting. But that is a different discussion.

We agree on that, but you were responding to someone who was specifically just one stop underexposed from ambient. That's still plenty of ambient light, so ETTL will probably react to that.

I was shooting that way earlier this evening. I wish the EXIF contained the flash power so we could see exactly what the flash contribution is.

On most Canon D-SLRs there is a setting in the Custom Functions to force the shutter speed in Av mode. Newer ones can force a 1/60-1/200 range. Older ones (like the 5D) can only force 1/200.

AntonLargiader wrote in post #12974273
We agree on that, but you were responding to someone who was specifically just one stop underexposed from ambient. That's still plenty of ambient light, so ETTL will probably react to that.

^This

I haven't used an external flash yet, so thought I'd learn something while adding for the OP's benefit because that is pretty much what he's trying as well albeit in a different lighting situation.

I would assume E-TTL would react and power up flash to compensate otherwise wouldn't that defeat it's purpose?

tman2782 wrote in post #12975769
^This

I haven't used an external flash yet, so thought I'd learn something while adding for the OP's benefit because that is pretty much what he's trying as well albeit in a different lighting situation.

I would assume E-TTL would react and power up flash to compensate otherwise wouldn't that defeat it's purpose?

This is the tricky bit with flash; you're really doing two exposures at once when using it.

Ambient light: Controlled by aperture, shutter speed and ISO
Flash light: Controlled by aperture and ISO; basically ignores shutter speed

So, you're getting the same amount of light contributed to your image at:
f/4, 1/100, ISO 200
f/4, 1/200, ISO 200

The difference there is the ratio of how much ambient light contributes to the image vs how much light the flash contributes to the image.

If the lighting is low enough, then either setting is going to get ALL of its light from the flash and produce the same exposure; regardless of the different shutter speeds.

Turn off Speedlite. Set to camera to AV mode at desired aperture.

Test shots till you get desired look for ambient (usually a bit darker than normal). Note suggested shutter speed for that aperture.

Go into M mode. Set Aperture and shutter speed as suggested by AV mode for desired effect.

Turn on Speedlite in ETTL mode. Test shots. Adjust FEC if needed.

Hand held, you'll get some interesting ambient movement. Tripod? Tell them to stand still and use a remote release.

Like this quick-grab (with A Better Bounce Card - YouTube) that doesn't look like flash at all.