Combining Aperture, Inverse Square Law and Power
Combining Aperture, Inverse Square Law and Power
Previously, we learned how to properly expose a photo using the Inverse Square Law. After that, we learned how to properly expose a photo using Aperture to control light. Today, we are going to combine those two and throw in another way to control the exposure of our photos while using off camera flash. This may seem like the easier of the three and it can be. However, you still need to know about the previous two methods in the event that you will need to use them together, like what we are going to do here.
Our previous two exercises in learning to expose photos properly involved us photographing a ball with our speedlight set on 1/4 power, our ISO set at 100 our f/stop set at f/5.6 (to start) and the distance between the ball and our speedlight at 12 inches and doubling that distance etc..
The starting settings for this experiment will be as follows: Shutter speed 1/125, ISO 100, f/5.6, speedlight power at 1/4 and the distance between the speedlight and the ball - 48 inches.
Now, take the picture..
ISO 100, 1/125, F/5.6, 1/4 power
As you can see, compared to where we started with our other experiments, we are closer to where we need to be. We took a little of what we learned about the inverse square law and started with our speedlight 48 inches away from the ball, so we have less light to start. Are we over exposed? Yes. However we are much closer to where we want to get.
Next, we need to lower the power output on our speedlight by 1 full stop. That means, we will take the speedlight from 1/4 power output to 1/8 power output. Keep everything else the same. Now, take the photo.
How does that look? Pretty close to our goal? We aren't quite there yet but you can see tremendous change right?
So, once again, lets lower the output on our speedlight 1 full stop. That will take us from 1/8 power to 1/16 power.
Take the photo.
The result? We've gotten so close to our desired look much faster than going step by step with the other experiments right?
Lets lower the output 1 more stop to see what it looks like. So, from 1/16 power down to 1/32 power.
What do you think? You can see the dirt on the ball, the scuffs, the seams.. there is nothing blown out....
As you can see, by adjusting power output of the speedlight can get you where you want to be very quickly.
Right now you're probably saying to yourself, "Self, that was pretty easy. But we didn't use what we previously learned" And you would be right, to a degree. We only used the inverse square law in that part of the experiment which leads us to our second phase of this experiment.
Now, we are going to incorporate using aperture into the mix.. The first phase, we had our aperture set at f/5.6. Now, I want you to start with all of the same settings listed above, but I want you to set your aperture 1 full stop higher than our f/5.6. By looking at our chart -
We can see that one full stop higher than f/5.6 would be f/8.
So, lets review where our settings need to be - 1/125, ISO 100, Speedlight on 1/4 power and 48 inches from the ball, F/8.
Take the shot...
What do you see? Slightly over exposed right? MUCH closer than our starting point at any other time, correct?
So, what is the next step?
That's right, lets drop the power on the speedlight 1 stop. So, we go from 1/4 power to 1/8 power.
Where do you think we will be with that?
Lets take the photo to find out..
What do you see? The dirt on the ball? The scuffs? The seams are clear etc.. But, it still seems a little bright.. what does your histogram show you? Any highlights blown?
Just for fun, lets lower the power on the speedlight one more time and see what happens...
As you can see, a full stop adjustment can make a tremendous change in a photograph.
Lets play with aperture a little more.
Here are the settings, ISO 100, 1/125 Shutter speed, Speedlight on 1/4 power and 48 inches from the ball. Now, lets close our aperture another full stop. Scroll up to look at the chart if you need to. We started at f/5.6, then we did f/8, now we will go to f/11.
We're looking pretty good from the start here...
Now, lets once again lower our flash output from 1/4 power to 1/8 power.
Here is what I got...
So, as you see, combining the Inverse Square Law, Aperture Control and Power output we can quickly and easily get to a properly exposed photo.
Remember, in real world use, you don't have to adjust by full stops. Most camera lenses and speedlights will allow control by 1/3 increments.
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