Wow, I love this place. Thanks for the prompt replies. Now, there are a few begging quesions. First, why the geryatric scale? Must be a Canon thing eh? Also, why in the hell would you even offer two settings that mean the exact same thing? 1/2 +0.7 is synomous to 1/1 -0.3 right? I also get 1/3 stop as .3 but 2/3rds and .7? Again, must be something elementary I'm missing here.
It's just rounding to one decimal place. A third is 0.33333..... and two thirds is 0.66666..... But because the flash can only display one decimal place, it has to round.
And you are right. 1/2 +0.7 is the same as 1/1 -0.3.
What do you mean by geryatric scale?
Another confusion I have is like in E-TTL I can adjust FEC to 0EV and +N EV, what about Manual, why can't I make more than full power output, or wait, I just answered my own ?, full-power is full power right...can't add more HP to a Hemi right?
Yeah. The flash can't get any brighter than full power.
Last, I'm just now learning what an actual stop is considered as so the following practical example is speaking aloud for my benifit and for anyone to critique.
Lets say I'm indoors and I expose for a portrait with the ambient light given and the flash on manual 1/2 +.3 and at ISO 200 I have a stop of f/4 and shutter speed of 1/125. Lets say I stop down one stop with the aperture and use 5.6 (is this right?). To compensate for this I would have to change the flash manual setting from 1/2 +.3 to 1/2 +0.7 or if I'm thinking with the left side of my brain 1/1 -0.3?
Whewww...time to read (I mean go to sleep) the Canon EOS Flahs articles.
Thanks,
Roy
A stop is just half the amount of light or twice the amount of light. if you increase the exposure by a stop you double the amount of light that is used to expose the image, and if you decrease the amount of light by a stop you are halving the amount of light.
So, in photography, you can change the amount of light in three ways: Changing the shutter speed, changing the aperture or changing the ISO.
If you double the shutter speed (1/250 to 1/125) then the shutter is open for twice as long and it lets in twice as much light. This increases the exposure by a stop. Halving it decreases the exposure by a stop.
If you double the ISO, say going from 100 to 200, then it also increases by a stop. Again, halving the ISO rating decreases by a stop.
Aperture is a little different, because it doesn't double when you increase by a stop. it increases by 1.4 times, because the aperture refers to the diameter of the hole that lets the light in, not the area. In order to make the area of the hole twice as large (which would increase by a stop), you need to multiply the diameter by about 1.4, not 2. Because the aperture is referred to as a ratio of the diameter of the hole to the focal length of the lens, the aperture value changes by 1.4 times rather than doubling or halving. So if you have an aperture of f4, you can increase it a stop to f2.8 (because 2.8 x 1.4 = 4, roughly).
When it comes to flash, the flash output can double to increase the flash exposure by a stop, or it can halve in order to decrease the flash exposure by a stop.
Notice that I'm saying flash exposure, not just exposure. Exposure is ambient light, but flash exposure is something different. For instance, imagine you are taking a picture of a person in front of the Eiffel Tower at night. Ambient light is going to give you the exposure for the tower, but it's going to leave the person as a black blob. So you use flash in order to expose them. So you have exposure (which shows the tower) and flash exposure (which shows the person). It's possible to have ambient exposure underexposed and the flash exposure over exposed. Just use a really short shutter speed, a wide aperture and a full power flash. It'll look terrible. And you can have the opposite as well. The tower might be overexposed and the subject underexposed if you set the shutter speed and aperture to overexpose the tower and use an under-powered flash.
regarding your example, you are decreasing the aperture by a full stop, but only increasing the flash by a third of a stop.
if you have the flash on 1/2 at f4, setting the aperture to f5.6 means you will need to increase flash to 1/1 to compensate.
probably the best way for you to learn about this is to actually play around with it. Find something to shoot (a vase, a book standing up etc) with a background a few meters behind it. Set your camera to manual and the flash to manual. Take a photo and then play around with your flash power and aperture.
A side note: flash exposure is not affected by shutter speed. The duration of the actual burst of light from the flash is so short that the shutter speed doesn't really have any effect on it.