Tuesday, March 3, 2009
So in this article on the series of Pentax Wireless P-TTL Flash we will discuss how to do this by experimenting with the flash zoom and and observing the fill patterns.
In order to accomplish our goal of max fill with min spill over we need to put the flash and umbrella on a light stand.
Then at max flash zoom and the umbrella shaft inserted fully into the umbrella clamp (keep a safe distance between the flash head and umbrella material in the case that your shaft allows you to insert completely) we shot an image at a high aperture so it produces a pattern visible on the umbrella material. I used flash on manual 1/1 power, ISO 100 1/180 @ f32.
We then adjust the zoom wider until the pattern has completely filled the umbrella material. Now that we have a full umbrella we can slide the umbrella shaft away from the flash head every couple of inches and taking a photo at each increment.
When the pattern no longer fills the umbrella material we have just gone under the max fill pattern and we can with smaller increments slide the shaft closer to the flash head until we have a full pattern again in our sample photos.
Once you have your optimum flash zoom and shaft length mark the shaft with a permanent marker and write the flash zoom length on a piece of tape and stick it on your flash.
My final results with the Pentax AF540FGZ flash and the Westcott 43" umbrella were I had 2 marks on my shaft. One at 16mm zoom and one at 13mm zoom with the flash diffuser engaged. The 13mm diffused light completely filled the umbrella and produced a very soft light which I liked in the test photos of the umbrella. We'll see how this light varies in actual use further in the series.
Now you have completed the Umbrella Fill and are ready to start shooting with your lights. So lets talk about flash and exposure modes next.