Well, maybe I describe how I do.
The guide is really terrific. I have read quite some documentation on flash usage, but the way that the document is structured to explain the control of ambient versus flash light, is a very unique and useful description. I have not found any better.
My main application is mixed light situation, where the focus is on ambient light with just 1-2 f-stops of fill light from the flash in local areas of the image. Often in back lit situations. I have the camera on manual mode M (ISO fixed, aperture and exposure time as well), and the flash on P-TTL or P-TTL HSS. If I can not get it to work as I want, I put the flash to manual and determine the power needed myself.
I should also say that I have used flashes on Olympus Pen cameras and a Canon G15 quite a lot, and did never struggled (I also didn't really understand, it just worked). On the Pentax, initially I was having a hard time to get to what I used to be able to do with the Canon and the Olympus. In Olympus world you select fill ligtht and in most cases you are done. Today, with help of the Pentax flash guide, I can manage quite easily in 99% of the situations.
As often, if you can't get something done, you blame it onto the equipment. I rather quickly realized that many DLSR users struggle (independent of the camera maker), just as I did. I haven't figured it out fully, but to my simplified opinion, it is simply that the compact and system cameras without mirrors have access to focus information during flash operation. I.e. the camera knows which area of the image the user wants to have in focus and link the flash exposure to that when they determine the flash power for the fill light. Using the view finder of a DSLR, the focus information and the exposure information are determined by 2 separate sensors in the bottom of the camera, independent of the image sensor. Since the mirror is in the line of sight to the image sensor, the image sensor gets no information. So the light meter sensor of a DSLR has to do the job alone (or in combination with a flash sensor). To my opinion, that is causing the trouble for DSLRs.
What I also love to have is getting the information needed into the view finder such that I don't need to take the camera down. With the electronic viewfinder this just normal, for the Pentax, the procedure below allows me to do so.
One comment regarding the ambient exposure in the flash guide p25-p27, from my perspective. The way it is explained is great for understanding. Just. The camera measures the integral light either in view finder mode (with the dedicated sensor) or in live view mode (with the image sensor). It can not do any different. Camera Metering = Ambient Light + Flash Light. The pre-flash is only triggered on the K-S2 when the exposure is taken, not during metering. Normally those flashes (pre and main) come so quickly behind each other, that you can hardly detect there is a pre-flash. If you select the 2 sec timer, they are clearly separated on the K-S2. But since there is no pre-flash during the metering, there will always be some uncertainty in P-TTL flash mode, how much flash light is added, because only with the pre-flash light the camera metering will know the contribution of the flash light to the image. Flash and camera set the required flash power based on the camera metering information and the flash information (distance, ...). This is my simplified understanding.
My Pentax procedure:
- Camera K-S2 with either the pop-up flash or the Metz 64 flash
- camera on manual mode (ISO fixed, Aperture set, Green bottom on Tv-Shift)
- flash on P-TTL mode (or if I expect exposure time less than the sync time, I set it to P-TT HSS mode)
- flash is out, I use the exposure compensation to the setting I prefer (mostly slight underexposure of the ambient light), then I push the green bottom, which set the exposure time considering the exposure compensation set
- I turn the flash on
- take the image
- mostly, for the first image of a setting, it is not quite right. So if I have too much or not enough flash light, I correct the camera exposure compensation. How much I need to correct depends on the reach of the flash in the image i.e. how much percentage of the image is influenced by the flash light.
- I retake the image
The procedure above may look complex, but it is not. I could also use the flash compensation to correct the flash light. But what I like about the procedure above is, that the exposure compensation can be viewed in the view finder, while the flash compensation can not be viewed in the view finder. If the flash light has only a very limited influence on the total image light, it is better to go to flash manual mode, rather than what is described above.
Feed-back on the above or corrections because of wrong understanding I would appreciate.
