Your going to be using flash for two purposes generally – either as fill-flash (FF) to lower contrast and fill shadows or as flash as main light (FAML). With FF, you first determine the ambient exposure required (this is the camera exposure w/o flash) to produce an image with highlights in the right-most histogram box w/o clipping. Then you add FF to fill the shadows. Usually -1 flash exposure compensation (FEC) is a good place to start in a auto mode or 1:2 or 1:4 in a manual mode on the flash.
Because this is FF, the histogram will change very little and in all likelihood the FF will not even be noticeable in the histogram. This is where you need to look at the LCD and see the affect in the shadows. The reason you can’t see it in the histogram is that you are only filling the shadows with light and lowering you mid-tone contrast. Of course you can overpower the flash enough to cause over exposure in which case the histogram and highlight alert will tell you what’s up. WIth FF, if the flash did not go off, you still have the correct exposure for ambient.
With FAML, the flash is the primary source of illumination and you will use the histogram here to determine if clipping is occurring. In manual mode, setting it to 1:1 will yield balanced ambient/flash exposure or FAML as long as the distance to the subject matches the distance scale on the flash. If not, you need to adjust aperture or ISO to get the distances to match. If you use the beamer, you are increase flash output about 2 stops, so divide the distance to the subject be two and get that to match the flash scale.
Or, use an Auto mode (ETTLII on Canon) and start with 0 FEC and increase as needed to get a good exposure. Aperture and ISO influences the flash exposure and shutter speed the ambient exposure. You can get a dark BG by increasing the shutter speed. With FAML, if the flash does not go off the image is under exposed.
I like Robert's explanation Doug !!!! Lots of good info !!!
Can also suggest a couple of points. You did not mention the lens used or if you had a better beamer on? At close distances is best to leave the BB off since it will over flash.
Files coming out without processing can/will look "not right" out of the camera When you push data to the right the overall appearance of the image can be very light which will look fine once its processed.
Regarding the histogram remember it is difficult to see in bright light The Mk2 does not have a particularly large window. Canons in genera are very difficult to see where the histogram ends. The new Mk3 is probably the worse one. On the other had with the Nikons is very easy. The histogram has a red border and its yellow.
One other thing I can suggest is to bracket with the flash If you fire two rapid images (or three) you will be getting different amounts of flash. The first is at full power, the next will be less since it will fire but not to full capacity and with the third the flash would probably not fire at all. I do use this technique a lot !!!! Will give you a strong visual of what you are doing and the effect of the flash !!!
I was using the Better Beamer on my 600. Sorry about that.
RA...
Unless I'm totally dense, so it sounds like I did the right thing...I set
for ambient first, then flash, then watch the lcd.
Alfred
I guess in a way I do bracket. I'll take the flash exposure, then immediately
take the second, knowing the batteries won't recycle fast enough. Its an idea
I read from Artie's second book, where he mentioned that if the flash failed to fire
he'd still end up with a properly exposed image.
This way if I totally screw up the fill flash, at least the second image I can work on
in post...I hope :)
Thanks for filling in some of the things I did not get to Alfred. Had to rush off to a meeting. So I think we got just about everything covered for Doug.
Doug, Alfred brought up a good point on processing the image. As long as you don't have anything clipped in the highlights you should be able to get a decently exposed flashed image to work with once you spread the data out using a levels adjustment. If the image looks overly flashed when using fill-flash, you need to use less flash output.
I played around with the JPG Doug and you are right the red channel is clipped. I am guessing that is because the ambient exposure was too much - typical that the red channel goes first in the daylight. It also appears that too much flash was used as the bird and bird house is very flat in tonality. I had to pull the stops out to get it too look a little better.
If -3 FEC is still too much, pull down the flash diffuser as that cuts the output a lot. You will probably then have to add more flash output to get where your going exposure-wise.
I played around with the image a little also. I only spent a couple of minutes on this, but although the reds are clipped, it does look to me like the image (as far as color is concerned, could still be salvaged.
Flash and Histogram Help
