I've been a little surprised by the number of emails I've received in the past few months from Pentaxians complaining about "fill flash" not working with the 540 and their K10D in daylight. While in many cases, I think the problem was that some of these folks had the flash pointed at the subject and not bounced correctly, it's hard to discuss "fill flash" without an example of how it's typically used.
I was reminded of this yesterday, as I had to shoot a wedding. Although this is a photo of my very helpful and patient assistant during a quick lens change between photo sessions, I think it's a pretty good example of nicely controlled "fill flash".
Whenever I use fill flash outdoors for portraits or causal shots of people, I always try to balance the flash with the ambient light, so the photo does not scream flash. When done properly, fill flash gives your subject nice separation from the background, and there should be a minimum of shadow created by the flash. In this photo you can see some shadowing from the flash on the right side of her legs, but I don't find this too distracting. The other "telltale" sign that you've used fill flash is the presence of a catch light in the subject's eyes. In this case it's quite small due to the size of the 540 flash head, and adds a little "pop" that I find appealing.
This photo was taken with the K10D set to wireless mode. The camera was in my right hand and I was holding the 540 in my left hand with my arm reaching as high as I could stretch so the flash and Stofen bounce (set at 45 degrees) was cascading light down over my assistant and the bench. Although I didn't need to for this particular photo, in many cases where the ambient lighting is weak, I'll reduce the strength of the flash by a 1/2 stop or 1 stop as needed.
I hope this example is of some help to a few folks that are still experimenting with using "fill flash". The only other advise I can give is that proper use of "fill flash" is not something that comes automatically by popping the flash on your camera and firing away. It actually takes a lot of trail and error, and careful study of your subject matter and the ambient light that you are dealing with.
