It seems like Aperture is one of those things that is perpetually confusing to people (I base this in part because it took me so dang long to feel like I really had a handle on it)!
Of course, it's also one of the most important concepts to understand when working with a imaging device (like a camera), so it's worth a little investigating.
What is Aperature?
- The aperture is (simply put) the size of the opening in a given lens.
- It controlls how much light the lens allows in
- Most aperatures are mechanical devices that vary in size (in other words they can open wider or close down smaller to let more or less light in)
- Every single lens has an aperture (simple lenses like the lensbaby have a fixed aperture system)
- Aperture settings are generally referred to as 'f-stops', you will usually see this as f/2.8 (for example where 2.8 is the size of the opening) or even just 2.8 to those in familiar with the lingo
- Even your eye has an aperture (the pupil)! It varies from around f/2.1-f/8.3
Here's the tricky thing (oh, now he tells us it's going to get tricky):
Changing the size of the aperture affects multiple aspects of a photograph (some dramatically!):
- One of the most obvious changes that result from fooling around with your aperture setting is the Depth of Field. (DOF) If the aperture is very small...there will be a large amount of depth. If the aperture is very large there will be a small amount of depth. Got that? Small ap. = big depth, big ap. = small depth.
- If that wasn't enough to worry about changing the size literally affects how much light comes in so...you guessed it...you are changing your exposure as well. Small ap. = only a little light in (slow, takes longer to expose), large ap. = lots of light quickly (fast, shorter exposure).
- If that wasn't enough...aperture will also influence various types of visual distortion - most lenses have a 'sweet spot' where at a certain aperture the lens will be most sharp and claer with the fewest possible abberations.
So let's look at a quick example of some different settings and how they impact an image:
FYI, these were shot at 85mm and they've all had the exact same post processing which is to say, virtually none.
Ok, so here is our first image. Please forgive the setup, it worked in a pinch (let me just thank my 3 year old son for the props).
The focal point is set squarely on the little blond girl (maybe blonds do have more fun?)
This was shot at f/22 (aperture) and it required a 2 second exposure.
At f/22 we should have a pretty big depth of field right? And we do...we can see all the toys pretty well (the dino is a bit soft) but it did take a pretty long exposure (2 seconds!). Nothing we could handhold.
Here we go with our second shot.
This was shot at f/16 (aperture) and it required a 0.8 second exposure.
Hmm, that's pretty interesting...look at how much the exposure time dropped.
However, do you also notice we've lost a bit of depth? Look at the dino now. He's starting to look plain blurry.
For our third shot we can really start to see some changes.
This was shot at f/8 (aperture) and it required a 1/5th of a second exposure.
We have another dramatic drop in exposure time.
How about our depth? Dino is looking like a Monet, and the girl in the pink dress is blurry also. You can see the forward edge of the table is fading as well as the far side of the monitor.
Wow, there's not much that is very sharp now. I bet we are getting some very fast exposure times now. Let's take a look.
This was shot at f/4 (aperture) and it required a 1/20th of a second exposure.
This image took 40 times less exposure time than the first one!
We are really narrowing that depth.
Almost done.
Blondy is still looking very clear, but tigger and cow are suffering a little. Dino is long gone.
This was shot at f/2.8 (aperture) and it required a 1/40th of a second exposure.
Notice how the heads of the two toys behind dino are sort of 'pushing up' against the top of the keyboard? If you check the first image they aren't even close! I don't have time here to cover this in depth but very narrow DOF shots allow light to bend and distort in some unusual ways.
Ok, last shot.
Only the little girl remains sharp. You might notice a little section of the keyboard also is sharp...it's exactly in line with where the girl is in relation to the film (sensor) plane.
This was shot at f/1.8 (aperture) and it required a 1/100th of a second exposure.
200 times faster than the first shot!
Final Notes:
- The shape of the aperture (typically the number of blades) determines precisely how the out of focus area will look.
- A higher number of blades (more expensive, more complex) will lead to smoother, more natural looking out of focus blur
- Lenses that can open their aperture very wide are usually called 'fast lenses'
- Some lenses (zooms) have variable maximum apertures - in other words, if you are zoomed out (or in) they might be able to open wider (or less wide) as the case may be.
Here's you super bonus extra credit trivia question!
(BTW, this is a hard one...I know a lot of photograpohers who can't answer this)
What does the aperture number actually represent?
Cheers, -B
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