Camera is set for external flash only but built-in is adding exposure.

<p>I'm a Nikon CLS user but I'm helping someone with a Canon system. She has the camera set for external flash only. We were getting some strange shadows on the wrong side of the image (the same side of the subject as the key light) and the background was getting light where it shouldn't.<br>

First I tried positioning the slave light in a bunch of different positions. Then, after suspecting that it might be the built-in flash, I turned the key light around facing away from the subject. It was definitely the built-in flash.<br>

I confirmed her settings and everything is set the way it should be (unless there is another setting I'm missing).<br>

Is this an issue with her camera? A firmware issue? A known issue with Canon's system?<br>

She's using a Canon 70D with a 600 speedlight as the slave.<br>

I appreciate any insight anyone might be able to provide.<br>

</p>

<p>It's impossible to say much without a photo and EXIF data but I'll take a stab in the dark since I use a 70D with Canon Speedlites. I've never encountered any issues other than me not reading the manual carefully!</p>

<p>First, if you're using flash with Av or Tv mode, Canon cameras default to fill flash no matter what the shutter speed (Nikon is different). That is, they expose for ambient light and use the flash to fill in shadows. If this is not what you want, use M mode and set exposure a few stops below ambient. The flash will then act as main light. You have to ignore the meter or you'll end up with the same results as Av mode: perfect ambient exposure with fill.</p>

<p>Second, I assume you're triggering the big flash with the popup? Be sure to set desired flash ratios in the flash menu. I don't remember what the default ratio is but it's set to work with the slave. I normally use a ST-E2 trigger so I can use physical switches but the menu is actually more flexible.</p>

Thanks puppy.

 

Some response details. She is shooting in manual mode with the shutter speed and aperture and ISO all set to

provide ambient Fill.

 

She also was only using the single slave mode so there were no ratios to set. She simply set the remote slave to provide one

stop over exposure which was necessary because of the light modifier. The pop up flash should have only been

triggering the slave and not adding any exposure.

 

By turning the key light away from the subject we were able to demonstrate that the pop-up was adding a lot of exposure

and creating a shadow on the background being that it was the only light facing the subject.

 

Thanks

 

Matt

<p>I don't think I've seen a solid reference for how much light the pop-up flash emits when it's being used to control external flash units, but I have seen some comments that in some circumstances it can have a noticeable effect on the scene. Obviously if you're shooting at ISO 100 in bright day light, it's not going to cast shadows; at most you might see a catchlight in your subject's eyes. But if you're (say) shooting in a darkened room at high ISO, perhaps it would be enough to be noticeable in the final picture.</p>

 

<p>I know you say it's adding "a lot" of light, and it would be hard to imagine a situation in which merely using the pop-up flash to control a slave would get that high, but I thought I'd throw it out there just in case. A sample photo or two might help.</p>

<p>Since you're using the external flash as fill, rather than mains, perhaps a gel filter before the popup would reduce its output enough while allowing it to trigger. The ST-E2 has a red filter and I've never noticed it interfering with fill or main flash output.</p>

<p>NM</p>

<p>I'm working on getting images from her. <br>

She is using the external flash as the Main light and ambient as fill. The pop-up should only be communicating with the external flash. The ST-E2 doesn't have a flash bulb to add any exposure to the image. I've suggested that as an alternative, but she should need it to do what she's trying to do.<br>

This may just be a case of getting it repaired. I just wanted to avoid that option if it's not broken, but just user error. From reading the manual and checking her settings, she's got everything set the way it should be (that I'm aware of) but there are lots of hidden settings that can affect these things, so I figured I'd reach out.</p>

<p>Here is the comparison photo.</p>

<p>Lighting Diagram</p>

<p>That shadow looks too wide to be from the pop-up, which is very close to the lens axis. Could it be a reflection from the window glass? I realize that the shadow still appears when the main light is turned away from the subject, but what if it's turned off entirely? In other words, could it be getting reflected by the window glass even though turned away from the subject?</p>