All Together Now
So now you understand what each of the three variables does, lets look at how to put them together using Aperture Priority on your camera.
Basically in Aperture Priority mode you are setting the F Stop, and the ISO, and watching the Shutter Speed to make sure it doesn't fall too low. You can not actually change the Shutter Speed in Aperture Priority mode because the camera chooses the Shutter Speed it needs to expose the photo properly. When your Shutter Speed falls under 125 you need to either lower your F Stop or increase your ISO and that will in turn make your camera choose a faster shutter speed to use.
Different lenses have different minimum F Stops, but for the purpose of illustrating we will refer to a lens with a minimum F Stop of 2.8.
Here's a situation to give you an idea of how it works...
You are in a room that seems to have a fair amount of light coming in, so you set your ISO to 400. You are photographing two kids playing quite closely together on the floor, so you set an F Stop of 4 to get them both in focus. You hold your camera up to your eye and focus on one of the kids, the shutter speed reads 250 - Great! A fast enough shutter to freeze those little playing people - Shoot away! Then after a few minutes the sun drops behind a cloud outside and you have less light to work with inside, you check the shutter speed and it has dropped to 30... Bummer! We can't have that! So you need to choose to either up the ISO or lower the F Stop, or both. Perhaps you are cool with just focusing on one of the kids for a bit? You could drop the F Stop to 2.8, that's 2 stops down, which will allow the shutter speed to go 2 stops up - to 125. Even once you get to 125 Shutter Speed, you may want a bit of breathing room, so you could increase your ISO to 600, which would increase the Shutter Speed even more, probably to around 250 - Ace! "But what if I don't want just Johnny in focus? Betty is cute too!" Then instead of dropping your F Stop, keep it at 4 and accept the grain that's about to come into your life by upping the ISO all the way up to 1600 - these could be nice black and white photos after all!
Just make sure next time you go to shoot that you remember to put the ISO down as low as the next situation will allow you to. We have both had our moments of shooting things at 1600 ISO that we could have gotten away with shooting at ISO 200. Whoops!
This should give you an idea of why those cheap kit lenses can be really tricky to get good shots with in low light. A lot of them have a minimum F Stop of 5.6 when zoomed in - that doesn't give you much wiggle room with ISO and Shutter Speed! A lot of our in person Photo School students have gone on to purchase 50mm 1.8 lenses on our recommendation, these little guys are super affordable (around $180) and will let you go all the way down to F 1.8 - cool! They are a prime lens, which means you can't zoom with them, but it's a great way to make you move your feet to get the photo you want!
The best way to figure out how to set your camera to Aperture Priority and how to adjust the F Stop and ISO is by googling your camera model - there are so many cameras out there, we can't put the instructions for them all in here!
We know this is A LOT to take in. We are dedicating this Wednesdays online chat to big cameras only (don't worry, you can ask us other stuff the next week, or if we have time at the end of the session)
Go forth and take photos in Aperture Priority mode. Take photos of whatever interests you! Keep in mind all the things you learnt about light and composition in the earlier lessons. Practice makes perfect(er)