I am having a ton of trouble with the Equations Worksheet II. I have gone over and over the examples in the Lecture and cannot for the life of me figure out how to do the equations correctly with the changing of ISO. I am getting so discouraged. Is there any additional material that could help better explain how to do them? Thanks so much for your help.
I am happy to help you with the EEII. I looked up your results with EEI and see that you understand how if you make your shutter faster, then you need to open the hole in your lens more to compensate.
The EEII worksheet is just like the EEI, but with just one more step added.
Do me a favor and go get your camera. For some students it is easier to see what is going on with their cameras, then to look at numbers on a screen.
OK, I am going to trust that you have your camera in your hands. Now, set it to:
100 F/8 @ 1/60
Great, we now have our base exposure. All we are going to do is move some of the dials around equally so that the same amount of light enters into the camera when we are done.
The equation we are looking at is:
100 F/8 @ 1/60 = 800 F/___ @ 1/250
When we look at it let’s just break it down into two parts. The first one is the part you already know. We are going to ignore the ISO change for now and just look at the needed aperture change.
F/8 @ 1/60 = F/___ @ 1/250
Counting the clicks, how many clicks does it take to quicken your shutter to 1/250 of a second from 1/60 of a second?
(Go ahead and count, I’ll wait.)
If your camera is set up in 1/3 of a stop increments, it will take six clicks. This means that your camera is now set to being two stops darker than is was just a moment ago. To correct for this, we need to open the aperture by two stops or how many clicks? Yes, 6 clicks! Go ahead and do that. Change your aperture so that will let in six clicks more light.
Now, what number did your aperture land at? F/4, right! (If you got F/16, then you turned your dial the wrong way and let in less light.)
You now know that F/8 @ 1/60 will let in the same amount of light as F/4 @ 1/250.
Now we need to add in the ISO change to the camera. Keep your camera at F/4 @ 1/250 for now.
OK, consider this, when you are shooting in a darker situation, you may need to increase your ISO to compensate for the lack of light. You are making your camera’s sensor more sensitive to the light. Sometimes we don’t want to give up our depth of field nor the shutter’s speed, because we will not be able to create the image we want. In these cases, we increase the ISO. Other times we may want more depth of field from our aperture than we currently have. In this case, we can change the ISO for this too. (Same is true if you want a faster shutter speed.)
Fortunately, ISO increases happen in full stop ranges too. They go from 100 to 200 to 400 to 800 to 1600 and on… Moving right starting at 100, you are making the image brighter in your camera.
Now that you know this, answer this question, if you go from ISO 100 to 800 how many stops brighter is your image? Go ahead, figure it out if you have not done so already. Did you come up with three stops? Good, that is the right count. Moving from 100 to 800 with the ISO will make your image 3 stops brighter.
Now you need to correct your current f/4 aperture setting to compensate for this. What setting with the aperture will give you three stops less light? Go ahead and look at your camera to figure it out. (Remember, you will need to click the aperture three times to create one stop of change. This means you will need a total of nine clicks.)
What number did you come up with? F/11. Right. So…
100 F/8 @ 1/60 = 800 F/11 @ 1/250
When you are working with exposure equivalents, just take it one step at a time. Start by finding out the aperture or shutter speed change first. Then figure out the ISO change.
Once you understand how to control this, do know that it will never change on you. These numbers are based at the speed of light. The numbers will stay constant as long as the speed of light does.
Do let me know where the questions arise. If algebra is more your speed, I can explain it this way too.
All the best,