Capturing the Moment

TAKING PHOTOS OF WHAT YOU REALLY SEE

Volume 1: Observe, Aim & Capture.

Key to many photographs is how much of the photograph is in focus.To understand how to get this right, we first need to understand Aperture and what it does.If we get it right, the object will be in focus, and the background slightly out of focus.If we get it wrong, we cheat...

CHAPTER 5

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Plumbing the Depths

This chapter is all about the aperture of your cameras lens. An aperture is a hole. That’s all. Nothing mystical, just a hole that lets light into your camera.

The same thing in the eye is the pupil, the black hole in your eye, the size of which is controlled by the iris, the part that also gives colour to your eye.

In controlling the opening in front of the

lens of the eye, the amount of light entering is changed. The bigger the hole, the more light enters.

Having spent much of the last year having my eyes poked about for reasons of health reminded me how easy our human eye specialists have it.

I too have spent much of my life poking about with eyeballs, but my patients were generally not as compliant as we humans. I’m sure

there are human exceptions to that, but bear in mind that close to the eye of an animal is usually an impressive array of teeth.

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Setting: U1Altered: None

The magical experience of looking closely into the eye of a Rottweiler can be somewhat reduced by the sound of a primordial growl emanating close to your ear.

This growl can be useful as an early warning system. Just before sinking their teeth into you, most dogs give off none too subtle hints, hints I am fully prepared to respond to with rapid movement in the opposite direction.

I may have mentioned that my favourite dog is a Golden Retriever. This has not always been the case. When I first qualified as a veterinarian, I discovered to my dismay that not all Golden Retrievers were equal. There was a condition rampant in the breed then called the ‘Rage Syndrome’. Diagnosis was easy; you got bitten. They would bite without ANY of the normal signals given off before turning man-killer.

Owner enters the consulting room:

Me: “Why hello Mr Kringe-Worthy” (Name changed to protect the guilty), “Good to see you today. My what a handsome dog you have there, what big floppy ears he has got.”

Mr K: “Allo Mr Vet, yes, ‘e is lovely ain’t ‘e? I am a little worried though ‘cos my Mincer has got a sore nose.”

Me: “Ah, what an interesting name and oh my! what a big nose he has!”

Mr K: “Yeah Mr Vet, could you take a close look at it and tell me whats wrong? Maybe there’s something in his eye?”

Me: “Oh my! What big eyes he has!”

Me (again): “AAAARRRGGGHHHHHH!!!”

Mr K: “Oh yes, perhaps I should’ve mentioned; he’s a bit touchy...”

Me: “My, what big teeth he has...”

Thankfully this trait has bow been bred out of them. Who says genetic manipulation is a bad thing?

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Setting: U1Altered: None Setting: U1

Altered: None

Now the camera on the other hand has no teeth, but does have the equivalent of an iris called, you got it, the aperture.

This hole lets the light in. Soooo....the bigger the aperture, the more light is let in. OK? Take your smaller than average dog, say, a Yorkshire Terrier. It’s mouth can bite (such fond memories) but cannot bite off a great deal of your anatomy. Maybe a finger tip or two at a time...

A Rotty on the other hand (depending if, by now, you have another hand left) can both bite and remove a significant amount of appendages at the same time. Thus the bigger the aperture of a dogs mouth, the more of you it can internally digest. In the case of a lens, it is not body parts, but LIGHT.

The more LIGHT that gets through your lens onto the sensor at the back of your camera, the faster you can make the shutter speed thus freezing something that is in motion.

So far, so good.

Now comes the tricky bit...

There is another affect of the size of the hole in a lens (can I call it aperture all the time now?) It also changes this mysterious thing called ‘Depth of Field’.

For the veterinarians amongst you, please don’t confuse this with the depth of poo you have to stand in whilst removing a cow’s afterbirth at 3 in the morning in the middle of a field.

Now we are talking about the RANGE OF FOCUS.

It is NOT immediately apparent why changing the aperture (ok to use that word?) should affect focus. After all, I’ve already explained how focus is achieved by moving the lens backward and forward (unless you are a mammal). Why should changing the width of a hole (er... aperture) affect the focus?

Here is an example of a large aperture:

That photo may help give you respect for aperture, because that kind of aperture really does have teeth...

So Let’s look at what is meant by depth of field.

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The easiest way of doing this is to give you some examples...

Here are two examples of different depths of field:

This is a picture of a tree taken from down below in its nether regions

This magnificent tree, covered with parasitic vines (another of many examples of the cruelty inherent in nature) is in focus from its bottom (hehe) to its top. This was achieved by closing the aperture down all the way to f22.

This picture however has only the magnolia flowers in focus, the background is blurred. This makes the flowers stand out from the background, but still leaves the background important in the overall photo. In this photo the aperture was opened right up to to i ts maximum.

So why does this happen? Why does opening the aperture reduce the depth of field (range of focus)?

Who cares?

Setting: U2Altered: f22

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Setting: U2Altered: None

Well, I do, but there is a reasonable chance that you don’t. If you really want to know the details of refractive indexes and zones of confusion and all sorts of deeply anorak-like stuff, feel free to google it. It is interesting, but not vital to the se of a camera. Do you use a computer? Do you understand how it works with its random access memory, its TCP/IP’s and its little gnomes with abacuses? Do you own a dog or cat (technically the cat owns you)? Do you know how it works with its loops of Henlé, its zygapophyses and epididymis's?You have to be marginally weird to want to know all these things.

I am a little weird, but then several years of university and Monty Python have that effect.

For the rest of mankind, here’s all you need to know:

Small Range of Focus = Small aperture number

Large Range of Focus = Large aperture number

Thus to focus on an object but have the background blurred, use a low aperture number (also called F-stop) such as f5.6 or less, if you want everything in focus use a large aperture number such as f11 or more.

In practice this means switching the command dial to U1 or U 2 then turning the aperture dial until you can see the required value in the viewfinder.

Magic.

Setting: U1Altered: None

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... and if the focus range is not right; cheat. (See how to cheat in Volume 2)

IS IT REALLY AS SIMPLE AS THAT?Well, no, not really, but this is perfectly fine to start with.

Once you have mastered the basics of Depth of Focus, you will realise that altering the aperture has weird effects on the other settings. The reason why I am advising the use of Aperture Priority is because I believe it to be the most important of the settings you make on the camera.

However, every time you alter the aperture, the camera compensates for the change by altering other settings all by itself. (Unless in Manual Mode where you can change all the settings individually and really make a mess of your photo all by yourself)

Most obvious is the shutter speed setting. As you open up the aperture, the time the shutter opens for reduces. In most conditions this is what we want, thus by having the aperture wide open (this is our User Setting 1) we have the best of both worlds. The focus range is narrow and the shutter speed is high, so reducing any blur.

Going the other way will obviously have the opposite affect. The range of focus increases and crucially the shutter speed slows.

It may slow too much, causing a blurred image. This is why we sometimes have to use ‘S’, the Shutter Priority setting, so that we can fix the speed in moving objects to freeze it in action.

There are also other effects. The ISO setting can change. If there isn’t enough light getting through the lens (for reasons of the

settings you have used or because it is simply dark out there), then the camera has a magic trick up its sleeve. It can actually change the sensitivity of the sensor. Amazingly, this also happens in our eyes too. With us it is a relatively slow process involving chemical changes in the retina (our version of the sensor). In digital cameras it is instantaneous, a big improvement on the old days where we had to change the film in the camera to use a more sensitive one. We would carry with us films of different speed. They were measured in ISO units, an ISO of 100 being the standard, but going all the way up to a 1000 or more. The trouble was those high ISO films gave a very grainy picture, the bigger light sensitive grains on the film making it react better to lower light levels.

This change of sensitivity is clearly a really good thing, but it does have its limitations. Modern DSLR’s can go up to 52,000 and more. This means they can work in situations where our eyes cannot!

The downside is the same as with the old 35mm film; the higher the ISO the more the grainy the appearance. Top end cameras handle grain much better than cheeper and older models, but there is still a limit. In ALL photos I take, I check how much grain there is, and then reduce it in post-production. More of this in Volume 2.

This is therefore something to bear in mind once you have got your head around the basics. The amount of noise you get is especially important in HDR photography, as this technique ‘amplifies’ all the detail, including the detail that you don’t want...

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