Photo Lesson 9: Size is important!

Or more specifically size of aperture is.Well done by the way for making it this far.  I have got one last trick up my sleeve that I need to share in order for you to choose the correct camera for you, and to understand how to improve your photo’s by simple adjustments of your camera controls…  Let’s look at aperture magic.

Technical warning

Yes, again there are volume after volume of technical photographic information on this next subject, and if you are desperate to understand the next bit, then google or the local library is your next stop.  But I won’t be explaining it to you!  Seriously, you are just going to have to take my word for some of this or go off and research it on google.  The science behind this is extremely complex.  I hope I’ve given you enough of an appetite to do the latter, but trust me you don’t need to, you just need to understand what is happening, rather than why.

When is a hole not a hole?

Every camera lens has an aperture (iris) behind it to control the amount of light hitting the film or sensor, and it can range from being fully open (typically when it’s very dim) to fully closed (typically when it’s extremely bright).

The technical name for these apertures are “f-stops”. The theory behind these is one of the calculations that you can go and look up.  But basically the aperture range commonly looks like this:


The “f” numbers only have a couple of aspects that are important to us.   Firstly, they let you know how far open the lens is.  That is, if I say to you f16, you know its a big number which means a small aperture.  And if I say f2, then you know the lens aperture is quite wide.  That becomes important later when we get into the magic.

For any lens, it will have a range somewhere between f1.4 and maybe f45 or more.  But not all lenses include the extremes of this wide range.  For instance, my small 18-55mm zoom lens on my Nikon DSLR has a range of f3.5 – f22. Or f5.6 – f36.  What?    Well just complicate things, zoom lens have different aperture ranges depending on what the focal length is set to.  So my zoom lens, when set at 18mm wide angle, has a range of f3.5 – f22.  But at its telephoto zoom setting of 55mm, it is f5.6-f36.  My large telephoto 55-300mm has two ranges, at 55mm it is f4.5-f22, while at 300mm it is f5.6-f29.

My bridge camera is f5.6 – f20.

My basic camera also has a zoom range starting at f3.3 for wide angle, and f5.9 when at its furthest telephoto.  But it doesn’t display the f-no so it’s difficult to determine what the smallest f-number is without getting the manual out – and it hardly matters if you can’t adjust it.

And just to confuse things to the nth degree, some cameras, like mobile phones have one single fixed aperture, maybe f2 – I.e. always wide open.

A very important thing to note is that each f-stop increase doubles the amount of light captured. Or halves it if you are decreasing in f-stop.  So for instance, f2 is double the amount of light that gets in using f4, and f1.4 is twice the light of f2.8.  And f22 is half the light of f11.

You can see then that the difference in terms of light gathering between f1.4 and f22 for instance is HUGE!  f11 is double f22 x2, and f5.6 is double f11 (x4) and f2.8 is double f5.6 (x6) and f1.4 is double f2.8!


I can hear you asking why this matters?  Well, for two reasons.  One is when selecting your camera.  Remember light gathering is all about lens size?  The f number calculation is a good way of quantifying the light gathering capability of your lens.   A lens of f 1.4 for instance will perform fantastically in the lowest of light (when set at its widest available aperture of f1.4), while one with a widest available aperture of f5.6 is less able in low light.

Going back to my little zoom, at 55mm zoom the f number is a meagre 3.5 and the lens costs a meagre £145.    But a 50mm fixed (i.e. not zoom) lens with a light gathering capacity of f1.8 is £175, and with f1.4 it weighs in at £349!

So rule one – always buy the smallest f-number lens you can afford.  If you have for instance a choice of two compacts, and one has a minimum f-number of f2, and one has f3.5, I’d be swaying towards the one with the f2 lens as it should perform better in low light.

Let the magic commence

The second reason why the f-stop range is important is due to a quirk of nature.  Again, don’t ask me to explain why – plenty more people before me have already done that.  All you need to know for now is how this quirk manifests itself to you, the photographer.

And this is the quirk.  When you focus your lens on something, say a person’s face, then there is a point of perfect focus, and this is called the focal plane.  And then, for a distance in front of that focus spot, and for some distance behind, the picture will remain in focus, and then things start to blur.    The quirk is, at a wide open aperture, the distance of focus in front of and behind the actual point of focus is very short, maybe centimetres or inches either way – for instance for some wide open apertures like f1.4, if you focus on the eyes, you might find the tip of the nose is actually out of focus.   Yet for some reason, if you took the same picture at f22, then the distance in front and behind the subject is huge.  You can have trees standing yards behind the subject that remain in focus for example.  This effect is called “depth of field” and the rule of thumb is small apertures (like f22) give large depths of field, and wide open apertures like f1.4 give extremely small depths of field.

I’ve borrowed this diagram to try to explain.

Image result for depth of field diagram

And going back to our aperture diagram, the diagram below tries to show you how the effect of depth of field changes as you move through the f-stops, illustrating that a mountain well behind your subject can be made to be blurred at a wide aperture, but in focus along with the subject at a narrow aperture:


Now let me show you this “depth of field” in action.

Here’s a little shot I set up, where I am focusing on the toy dog at the front of the photo in both images:


Above: Shot at aperture f3.5, focusing on the robot dog’s nose.


Above: Shot at aperture f29 , focusing on the robot dog’s nose.

On first glance they don’t look very difference, but if you recall what we said about depth of field, at f29 (small aperture) things are still in focus much further behind the focus point (the dog’s nose) than they are at a wide aperture of F3.5.    While we can easily see the dog is in focus on both shots, let’s take a closer look at the toys in the background:

Shot at aperture f3.5                     Shot at aperture f29

As you can plainly see, at f3.5 the depth of field is small and the distant subject is well out of focus, while at f29 the image is crisp from front to back.

This effect is popularly used by photographers – in portrait work, it is common for the photographer to select a large open aperture deliberately as they want to send the background out of focus and make the viewer concentrate on the subject in focus.

Here are a couple of shots where I have deliberately set a wide aperture in order to make the background out of focus.


Notice how the grass and trees provide a nice green background to my granddaughter’s emerald dress.  The shot would not looked as good if the background was in focus – it would be distracting and take your eye away from the main subject.


Here is another shot of her, at another wedding!   Again the background is out of focus, the lavender stems providing a nice contrast to the colour of the dress.  But notice that the lavender directly at her side, at the same distance from the camera as her, is still in crisp focus.   It’s within the depth of field for the aperture in use.

One last image, this time from our holiday in Mexico, demonstrating how you can pick out your subject from a busy background by just throwing it out of focus.


So that’s photos taken at wide aperture.  But there are times when you want everything in focus.   Landscape shots are especially relevant here.  You might have some nice foreground detail, and nice midground, and something dramatic in the background, and you want EVERYTHING to be in focus.  Bring on a small aperture, increase the depth of field, and hey presto – magic happens.  Everything is in focus – examples…





None of these shots would work if the foreground or background was fuzzy


Ok, hopefully you have the idea how to manipulate your aperture to get the desired depth of field.    More importantly, hopefully you are realising that you can put a little thought into your shot and make the most of them.

Basic cameras

Without full control of your aperture setting, you are going to struggle to achieve these images.   Luckily, most basic cameras have a couple of settings that can help:


In portrait mode (often designated by a face, or a woman in a hat – at the top of the dial above), the camera is set to give a wide aperture and low depth of field, hence throwing both foreground and background out of focus.   In Landscape mode (normally a square with mountains in it, at the 3 o’clock position on the dial above) the camera sets up a narrow aperture to give greatest possible depth of field and get everything in focus.

So when choosing a camera, you need to decide the types of photo you will be taking. If you need to concentrate on a subject and take everything in front and behind out of focus, you need a lens with a very small f-number.   If you want everything to be in focus from the squirrel on your fence to the mountains far beyond, you need a camera capable of setting a very small aperture and a very large F-number.

You have far more flexibility with a camera with shutter and aperture controls than you get with a compact, so this should inform your choice further when selecting which camera choice is best for you.

To be continued


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