Aperture: A really really simple explanation (I hope) :)

By
Services for Real Estate Pros with Bryce Mohan Photography

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!): 

  1. 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.
  2. 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).
  3. 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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Rainmaker
283,750
Gene Allen
Fathom Realty - Cary, NC
Realty Consultant for Cary Real Estate

Thanks for the info.  I always get it wrong but my camera always gets it right.

My guess: these numbers are refering to the relative physical opening of the lens diaphragm and they use the f because it is a numerical expression that is equal to the focal length divided by the effective aperture of the lens opening

 

Oct 07, 2008 06:56 AM #8
Rainer
30,651
Bryce Mohan
Bryce Mohan Photography - Bellevue, WA

Robert, that's exactly right...narrow ap. = much faster exposures which sometimes eliminates the need for a flash.

Nelson, cheers. :)

Kenna, feel free to look through my blogs...there's plenty and it's not all so technical. :)

Cheryl, thanks...wow, I most certainly couldn't handhold that well (but thank you for thinking I could have!). No, these are all tripod shots via a cable release.

Michele, sure thing...hope it helps.

Maureen...this blog has earned you 4 credits. You're almost ready to graduate!

Lee & Gene, you both have similar responses. This are very well thought out and you are very close. It's actually just a bit simpler than you might imagine. :)

Here are three BIG hints:

  1. The aperture isn't related to focal length (though you are on the right track), if it was the relationship would vary wildly on tele lenses.
  2. Can you think of the most wide open aperture you've come across (small number). What was it?
  3. The aperture is physically changing size right...if you had to visualize that change (or draw it) what would be the easiest way to show the change?

Cheers, -B

 

Oct 07, 2008 10:19 AM #9
Rainmaker
211,662
Michelle Finnamore
Vaughan and Toronto GTA - Vaughan, ON
Preparing your property for sale

HI Bryce, great post.

I remember my first SLR camera way back in 1977. Had to learn all this stuff. No fancy digital cameras to make all the decisions for you.

The aperature measures the amount of light hitting the sensor in the camera. Is that close to being right?

Oct 07, 2008 10:59 AM #10
Rainmaker
252,037
Lee Jinks
Jinks Realty - McAllen, TX

The largest aperture Canon offers right now is f/1.2, but I think I'm aware of f/1.0 and some say f/.75 can be found on movie cameras.

Okay, I now understand why "f/".  It's "focal length divided by"...see?  f/

A 50mm lens at f/1.0 has a diameter of 50mm  (50mm/1.0=50mm)

The same 50mm lens at f/8 would have a 6.25mm opening.

But this is just another way of saying that the f-number is focal length divided by diameter of the opening or aperture.

Oh, but I see another glint of familiarity.  Most of the fastest lenses top out at f/1.4 which is roughly the square root of two.  This corresponds to the amount of light hitting the sensor by a factor of 2 for each step in the aperture ring or setting.  The amount of light is halved for each step in aperture.

What I find interesting is that as the aperture gets very small, everything is in focus to the point where a lens isn't even necessary in a pin hole camera.  Is that cool or what?

I told you I was a geek.

Oct 07, 2008 03:25 PM #11
Rainer
53,227
Eric Lee
Realty Executives - Phoenix, AZ
e-PRO, SFR - Phoenix, AZ

Oooh, oooh - I know. . . .

The f number is the inverse ratio of the maximum amount the aperture may open (as permitted by the design of the lens) to the physical maximum that the aperture is capable of opening. The f number represents the physical dimension of the aperture divided by the number that follows to represent the amount the aperture actually is open thus f/22 (ie, 1/22nd) is a much smaller aperture than f/2 (1/2).

Lens focal length has nothing to do with it (except to the extent a longer lens is more difficult to design with a wide aperture).

Oct 07, 2008 04:37 PM #12
Rainmaker
270,923
Cathy Lee
CL Design Services Home Staging - Danville, CA
ASP, IAHSP, RESA Danville, CA

This is one post I will be reading many times-thanks again Bryce.  Always a great lesson for me when you post!

Oct 07, 2008 05:44 PM #13
Rainer
111,366
Toronto's 2 Hounds Design: Decorating + Staging
2 Hounds Design + Home Staging - Toronto, ON

You made this a fun lesson. I've had similar but not nearly as clearly stated and shown with such great examples...thank your son for me!

I'll bookmark this!

Oct 07, 2008 07:04 PM #14
Rainer
13,402
Dave Culbertson
Real Living Home Team - Mount Vernon, OH

Good presentation.

I have understood this for years,as I grew up around photography, but never was told what the numbers mean.

Oct 07, 2008 11:09 PM #15
Rainmaker
252,037
Lee Jinks
Jinks Realty - McAllen, TX

Bryce, you and Eric have told me that f-stop is not related to focal length, but how would you calculate the area of the opening of the aperture if you didn't have the focal length?  As I understand it, the diameter of the opening can be calculated by dividing the focal length by the f-stop.  Divide the diameter by two and you have the radius(R).  The area of the opening then uses the pi R square formula to calculate the area of the opening. (I know, pie R round; cornbread R square).

And I misread the question the first time.  I thought you wanted to know how to calculate the f-number, when what you had asked is what the f-number represents.  It represents the amount of light hitting the sensor.  And I agree with Eric that it's an inverse in that the larger the number, the smaller the aperture and therefore less light hitting the sensor.

The aperture is set in steps (sometimes referred to as stops).  Each stop represents a doubling or halving of the amount of light hitting the sensor.  If you start with the square root of 2 (1.41421356237) then multiply by itself you will get the next stop in aperture setting (2.0, 2.8, 4.0, 5.6, 8.0, 11, 16, 22, 32...)  The area of the opening is halved at each of subsequent stop effectivly halving the amount of light hitting the sensor at a given shutter speed.

Shutter speed?  What a great topic!

Oct 08, 2008 03:02 AM #16
Rainer
53,227
Eric Lee
Realty Executives - Phoenix, AZ
e-PRO, SFR - Phoenix, AZ

LEE - Been reading up on aperture and I think I have been misunderstanding it. You appear to be correct that aperture is related to lens length - that is what every site I have found says. BUt it raises other questions for me: since it relies on the formula area=pi * (f/2N)2 then does that mean that a 200mm lens set aat 4.0 lets in twice as much light as a 100mm lens set at 4.0?

Oct 08, 2008 05:29 AM #17
Rainer
123,471
Michael Cole
CPG Tours - Orange, CA

I don't know, but I think Lee got it in his last response. I learned the same thing, that each stop is either half or double the next one. Same thing with shutter speeds. Which makes it easy to determine the appropriate shutter speed when you change your aperture.

BTW - Great post Bryce!

: )

Oct 08, 2008 06:04 AM #18
Rainmaker
252,037
Lee Jinks
Jinks Realty - McAllen, TX

Bryce, how nice... Thank you so much.  I was concerned about sounding smug when in reality I'm learning from you.  I thoroughly enjoy all your posts.

Eric, as I understand it, the opening would have twice the diameter between a 100mm lens and a 200mm lens at the same f/4, but I don't know how that relates to how much light reaches the sensor.  I've exhausted absolutely everything I know to answer the last question.

Oct 08, 2008 06:49 AM #20
Rainer
30,651
Bryce Mohan
Bryce Mohan Photography - Bellevue, WA

OK, first off I was wrong. Lee is right! <- I wish i could make the font bigger!

Aperture is related to focal length. I think Eric had this sorted out also as did Michael.

Only the actual full time photographer *cough* (me) had any confusion on this subject. ;)

I'm going to leave my previous comments up (incorrect as they are) so folks can follow the progression of the conversation.

I'll fess up, I was looking for the relationship between aperture and filter size (there is sort of a dubious connection here but it shouldn't be relied upon).

Anyway, thanks guys for going into such detail! You win the coveted 'virtual' gift basekt! Wooo!

Oct 08, 2008 07:04 AM #21
Rainer
30,651
Bryce Mohan
Bryce Mohan Photography - Bellevue, WA

Lee, no sweat...it's great to have you stop by my blog and I'd much rather have my knowledge improved (corrected!) than the reverse. :)

Again, thanks for going into such detail on this question (and Eric also).

Cheers, -B

Oct 08, 2008 07:06 AM #22
Rainmaker
210,803
Terrylynn Fisher
Dudum Real Estate Group - BuyStageSell.com - Walnut Creek, CA
HAFA Certified, EcoBroker, CRS, CEP Realtor, Etc.

Bryce, a picture is worth a thousand words...So much easier to see when illustrated so well.  Thanks for the lesson.

Oct 08, 2008 11:08 AM #23
Rainer
71,384
Patt M. Judd
First Realty Company - Cookeville, TN
Realtor - Your Cookeville Connection

Great post Bryce... I certainly learned something today... and the pictures are great with the descriptions....

Oct 09, 2008 05:02 AM #24
Rainmaker
122,767
Susan Peters
Dove Realty Inc. - Seattle, WA
The Better it Looks the Better it Sells

Hey Bryce,

I just took a photography class and your explanation is so much clear. now i think I can do it!                                                

                                                       Thanks.

Oct 18, 2008 07:34 PM #25
Rainer
143,940
Christina Williams. REALTOR® TN property search & local insights
First Realty Company - Crossville, TN

Wow... Thank you!

Oct 18, 2008 09:37 PM #26
Rainer
42,261
Kayla Schill
CBH Homes | CBH Sales & Marketing, Inc. - Nampa, ID
New Home Ninja

Great work!

Dec 19, 2011 04:21 PM #27
Rainmaker
1,128,636
Inna Ivchenko
Barcode Properties - Encino, CA
Realtor® • Green • GRI • HAFA • PSC Los Angeles CA

i really struggle with aperture....I'm in a new relationship with my Nikon D7000 and not very skillful in A mode....

 

p.s. I don't know what is going on with AR today, but i can not see your pictures, so sad....i'm sure, they are gorgeous. I'll come back.

Apr 30, 2012 04:13 PM #28
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