RobertG wrote:
I hope someone out there can help me with this:
I'd like to take a christmas tree / family picture with my external flash, but I don't know how to adjust the exposure compensation for the ambient light on my t6i.
I'm in manual mode but when I push the exposure meter button on the back of the camera, it only brackets the exposure.
Does anyone know what I'm doing wrong?
Thanks for any help!
Bob
Hi Bob...
First, I am assuming your "external flash" is either a Canon flash or equivalent, with "ETTL" auto exposure capablities.
If that's the case, it's pretty easy to answer....
When your camera is set to M (manual) mode, the flash is the ONLY light source that's considered by the camera's metering system. So long as the
flash is set to ETTL (and not also to M), you actually are getting a form of auto auto exposure mode (even tho the camera is set to M), except the ambient light conditions are largely ignored. Think of this as "FULL FLASH".
When your camera is set to any of the auto exposure modes (Av, Tv or P), the camera meters ambient light conditions and sets exposure according to that, then during exposure the flash is fired at reduced power (usually -1.666 stops by default, tho this is adjustable).... This is "FILL FLASH".
In Full Flash and Fill Flash, you can use Flash Exposure Compensation (FEC) to dial the strength of the flash up or down. This works exactly the same way as Exposure Compensation when not using flash at all, in any of the auto exposure modes (Av, Tv or P).
You also can use Flash Exposure Bracketing (FEB) where you can set the camera and flash to make a series of shots at different exposure levels, which you set up. All Canon cameras allow you to bracket at least 3 shots... some allow more. This might be useful shooting Christmas lighting, which can be tricky. The camera will probably want to underexpose, due to all the bright lights in the image area. So you migth set up bracketing where one shot is taken without any adjustment, a second is taken at +2/3 stop and a third is taken at +1-1/3 stops.
Lacking some things like a separate flash meter, you're going to need to experiment and take some test shots. You'll have to try to achieve a balance that you like, between the flash and the ambient light. The number and brightness of of Christmas lights, other ambient light, as well as the power of the flash, how wide a lens you're using and the distance the flash needs to reach are all things that effect exposure.
I'd set my camera to M, stop the lens down a little for greater depth of field, and set a shutter speed at or below the camera's flash sync speed (1/200 or slower on your camera). Then I'd take some test shots without any flash at different h ISO settings to see what records the Christmas lights the way I want. Once that's determined, I'd add flash and take some test shots, tweaking it with different FEC until I got the results I want. Adjusting the lens aperture will effect the distance the flash reaches... larger will show greater distances illuminated... smaller will be more limited. Shutter speed doesn't matter very much as far as the flash is concerned, but does have significant effect on how ambient light is captured. If anything is moving in your images, you'll need to watch out for "ghosting" that can occur when mixing ambient light and flash. (That ghosting effect can be useful to give images a sensor of movement, but to "look right" often will require you set the flash to "Rear Curtain Sync".) Shooting Christmas displays in particular with flash, you'll also have to watch for how any highly reflective objects bounce the flash back at the camera.
The great thing about digital is that you get immediate feedback with image playback and the histogram on the camera's rear LCD monitor. The test shot method described above is pretty quickly and easily done. (It was far more difficult to get these types of shots properly exposed on film... where you had no means of testing and wouldn't know if you did it right until after you got the film processed.)
I don't have a T6i and don't know what specific flash you have (and there are differences in how FEC and FEB are set, with different models). Consult the manuals for the camera AND the flash. I'm sure you'll find the specifics there. If you don't have the manuals, they can be downloads in PDF format from the Canon website.