Beginner Aperture

The aperture is synonymous with the iris of your eye. A wide open iris (or aperture) lets in more light than a closed up or small aperture/iris. Referred to a f-numbers and they are a ratio so the smaller the number the wider the opening, i.e. f2.8 is wider than f11 and so f2.8 lets more light in than f11 would.
 
"small" aperture can be confusing terminology - I prefer to use "narrow" as a wide aperture has a "small" f number (eg f/2.8) and a narrow aperture has a "large" f number (eg f/22)
 
Depth of focus is the range of distance around the point of focus which is still pretty sharp. The smaller (narrower) the aperture the wider is the depth of focus.
 
Hi Erica, aperture does two things,it lets in more/less light and gives you more/less depth of field. DOF is also dependant on focal length and distance to the focal point, but I'd say don't worry about that just yet.

The smaller the number, (wide hole) the more light is let in but it also gives you a shallow (less) depth of field

Larger the number (small hole) lets in less light but gives you greater depth of field :)
 
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The 'aperture' is a hole behind the lens.
A 'big' (wide) hole has a 'low' f-number in the settings
A 'small' (tight) hole has a 'high' f-number in the settings.
Size of the hole can be adjusted, like a 'tap'.. mechanically by 'leafs' being arranged in a petal shape so that they can hinge to make the hole between them bigger or smaller, like the 'iris' in a human eye.
Bigger the hole, more light it lets through the lens, the 'brighter' your picture will be...
Smaller the hole, less light it lets in the lens, the dimmer your picture will be.
To keep the same 'brightness' of photo, or 'exposure', you need to 'balance' the aperture setting, f-number, against the 'shutter-speed' and ISO sensitivity - see 'The Exposure Triangle'.
Effect of different aperture settings on a photo is the 'Depth of Focus'....
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Snap-shot of my daughter on Llandudno beach, maybe less than ten feet away. She's fairly close to the camera, the buildings on the prom in the back-ground are over a mile or more away from the camera. With a 'tight' (ish) aperture, the 'Depth of Focus' is fairly large; both my daughter, close to the camera, and the buildings in the back-ground, and the pebbles on the beach, in-front of my daughter and between her and the prom are all in reasonably 'sharp' focus in the picture.
10610890_846149305409988_26696494051598845_n.jpg

Slightly 'tighter' framed shot, and now my daughter is still in focus, but neither the back-ground, nor the pebbles on the beach between, aren't and the street-lights on the prom have been reduced to less 'distinct' blurry rings.The 'depth of focus' has been reduced to only a foot or so, around my daughter, not 'entirely' created by using a larger, lower f-number, aperture, but this is the 'effect'.

The 'aperture' setting is only one factor in controlling the 'Depth of Focus'. The 'main' influence is the camera to subject to back-ground distance 'proportions'. Here, moving closer to my daughter, I reduced the camera to subject distance, and increased the 'ratio' of that to the subject to back-ground distance.. which also reduces the Depth of Focus. Other significant influence on DoF is the lens length or 'zoom' you use. Longer lenses or more 'zoom', tend to give shallower DoF.
 
droj said:
Phew. Blimey.
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....It's not quite as daunting as it might first seem when it's all explained so fully in words as Teflon-Mike has done!

Read it several times but then just try out the minimum and maximum f/ (aperture) settings on your camera shooting the same subject from the same position and compare the results when uploaded to your computer. You'll soon begin to see what does what.

The beauty of digital photography that taking photos costs you nothing and you can throw away what you don't want to keep.
 
Wow such a response! I'm going along to my first photography workshop tomorrow so all this will be useful to know. Will have to read them all again carefully! Thanks everyone :naughty::ty:
 
I do not wish to confuse you, or be too pedantic, but where people have used the term Depth of Focus it should really have been Depth of Field. This may save you getting confused at the workshop.
I may seem to be nit-picking but Depth of Focus is actually used for something different (all to do with the image being created at the sensor and not particularly interesting or useful at this point).
 
The f-stop numbers are a bit confusing, in that big number=small hole, small number=big hole. This is because the numbers are actually fractions. So f4=1/4, f8=1/8 and so on.
 
Very confused but happy to learn just might take a while :banana: thank you guys.
 
To add a bit more to f numbers.

F numbers are related to the focal length of the lens and tell us the diameter of the hole through which light enters the camera.

For example, if the focal length of the lens is 50mm and the aperture is set at f2 then the diameter of the hole is 50/2 = 25mm, ie quite large, so a lot of light enters the camera

If the aperture on the same lens is changed to f16, then the diameter of the hole is 50/16 = 3.125mm, ie quite small, so little light enters the camera.


The above is not strictly true as the amount of light entering the camera is determined not only by the size of the hole but also by the length of time for which the light is allowed to enter the camera, ie the shutter speed.



The result of the relationship between focal length and f number is that

a small f number, eg f2 mean a large hole, and

a big f number eg f16, means a small hole.


Dave
 
To some extent i'd say pretty much ignore most of what has been said above about the theoretical if's and but's, and just experiment for yourself with how aperture affects your photos (not that is is not good to know the theory, but as a beginner it can get confusing trying to cram all this new info into your head at once)

The best thing i ever did was to buy a fully manual 50mm f1.8 lens back when i was starting out, and it soon taught me not only what the aperture was (as you can see it opening and closing when selecting the aperture on old lenses), but also very quickly showed me what affect it had on my shots when selecting different aperture values

It's not so asy with modern lenses as by changing the aperture on the camera body does not change the aperture on your lens in real time, it only changes the aperture when you hit the shutter button

I suggest you set your camera to Aperture Priority mode and take a series of shot of the same subject but at different apertures, it should soon become clear just what the aperture controls, and that is the DoF (Depth of Field)
 
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Nostromo said:
The f-stop numbers are a bit confusing, in that big number=small hole, small number=big hole. This is because the numbers are actually fractions. So f4=1/4, f8=1/8 and so on.
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When is an aperture a hole? Or vice versa?
 
droj said:
When is an aperture a hole? Or vice versa?
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....I would have thought that any member of this forum who has posted over 1,500 replies and who has an image of a photographer (yourself?) as their avatar would know what an aperture is by now!

An aperture is defined as either an opening or a hole or are you being pedantic about @Nostromo 's sue of the word "hole"?
 
RedRobin said:
....I would have thought that any member of this forum who has posted over 1,500 replies and who has an image of a photographer (yourself?) as their avatar would know what an aperture is by now!
An aperture is defined as either an opening or a hole or are you being pedantic about @Nostromo 's sue of the word "hole"?
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Perplexed me too...
But then if I was being 'picky' with
Nostromo said:
The f-stop numbers are a bit confusing, in that big number=small hole, small number=big hole. This is because the numbers are actually fractions. So f4=1/4, f8=1/8 and so on.
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it would have been that the F-No isn't a 'fraction', which is an actual 'value' expressed as an half-done sum, but a 'ratio' which isn't a sum, but an equation defining the relationship between two commodities... in this case the diameter of a hole* in relation to the focal length of the lens.... you can use it to DO a sum, and 'get' a value, but on its own it's not a 'value', its a relationship.

y=mx+c is the equation for a straight line, it defines the relationship between two 'variables', X and Y. You have to 'substitute' actual values into it to 'do a sum'... 1/2 is a fraction, its a number, 0.5, an actual value. If we were to say that 'm' the gradient of our straight line is 1/2 or 0.5, it is then a 'constant of proportionality'.. but it is still a 'value'... now y=0.5x+c and if we say c is zero, we have y=0.5x or in words, y (aperture diameter) is 'half' x (lens focal length)... often short-handed to just say something is 'half' something-else, and used AS a 'ratio', but strictly its not, its still a 'value'..used as a constant of proportionality IN a ratio... but that is getting very pedantic!

* Purely for academic interest; Could get even more pedantic about 'aperture diameter', as usually lens apertures aren't nice round holes, they are hexagons or pentagons, or octagons or other multi-sided geometric shapes, and with curved 'leaf' aperture blades often not even nice regular ones, rather than a circle. So the 'diameter' is often imaginary, and that of a 'theoretical' circle of the same area..

Then delving even further into the science, the 'maths' gets even more imaginary, because very few lenses, actually have a 'true' focal length, or 'true' aperture size.
diagram.gif

'True' focal length is the actual distance fro the 'centreline' of the lens, to the focal plane it projects an image on.. for a 'simple' single element lens, like that one, which has an equal amount of 'bow' on the front and the back.. they aren't always, and these days seldom so 'convenient'.
ASlens.jpg

Where would the 'centre' of that "Meniscus" form lens on the end, be, for example?

media%2Fb59%2Fb5984aee-3114-4b9d-95c1-885171703e6b%2FphpD6Hm14.png

And which distance do you measure if you have two lenses, one behind the other? Which is what you have in most modern camera lenses, which is why in the specs they talk of how many elements a lens has and how many 'groups' they are arranged in.....

Looking at the Nikon Web-site, the Kit 18-55mm 'zoom' lens that comes with my camera has 7-elements, arranged in 5-groups.... cracking out the vernier gauge and trying to measure 'something', at it's 55mm 'focal length' the front element is about 92mm from the lens-mount... at the 18mm focal length, the front element is about 88mm from the lens-mount , and it's at its 'shortest' at around the 30mm focal length, when the front element is about 80mm fro the mount.... I am NOT poking the depth gauge of my vernier into the camera to find how far the 'sensor' is from the lens-mount! at a rough guess, it's probably 45mm or so..

This all suggests the 'sums' are all a bit of a nonsense... because focal length doesn't actually relate to any 'real' actual measurable distance! And neither does the aperture 'size'.

Interesting to note, that this lens, like many, changes 'physical' length with the zooms 'focal length'.. BUT, at the short, 18mm setting, it's a lot longer than 18mm, and at the 'long' 55mm setting, its still significantly longer than 55mm, and it actually gets 'shorter' in between the two..

Obviously, the 'Len-Length' as a zoom setting, isn't the 'actual' lens length in the physical world, 'something' is happening inside the lens, with these seven 'elements', individual glass lenses, and their 'groupings' that is 'equivalent' to an 'imaginary' single element, of that 'imaginary' distance fro the focal plane or 'sensor'.

So the 'sums' are all thrown to kilter by this working to idealised 'equivalences'... for both the focal length AND the f-number derived from it.

Two more useful points of note from this little deliberation;

First off; 'Variable Aperture' Zooms. That 'Kit' 18-55 is described as an f3.5-5.6 lens. The 'widest' aperture is f3.5 at the 18mm zoom setting, while at the 55mm zoom settling, the fastest aperture is f5.6. Racking through the 'zoom' range.... it becomes f4 at the 24mm setting, f5 at the 35mm setting, and the slightly 'odd' f5.3 at the 45mm setting. Offers some even 'odder' f-numbers at other settings in between.

This is 'sort' of explained by the fact that the F-Number is a 'ratio' of (equivalent) focal length, to (equivalent) aperture diameter. So, f3.5, at 18mm the 'equivalent' aperture size is a hole 18/3.5 or 5.14mm in diameter..... if you then 'zoom in' and increase the focal length from 18mm to 55mm, a 5.14mm divided by 55mm gives an f-no of 10.5... which gives us yet another 'anomaly' because specs say that the lens has an f-no of f5.6 at 55mm... but that would mean an 'aperture' of 55mm/5.6 or 9,8mm diameter, which at 18mm would give us an F-No of f1.8, which would be fantastic! That's as 'fast' as an expensive 'prime' lens!

So, again, the maths doesn't stack up. Either the hole changes size as you zoom, or it's neither 5.14mm or 9.8mm... or quite possibly a little bit of both! Explanation, is again in all these 'equivalences' and it depends in where i the lens the aperture is placed i relation to these moving 'elements' as to what 'equivalence' size it has n relation to its actual 'physical' size.

Important thing IS... its NOT actually 'important'! We don't really need to know how 'big' our aperture is, or indeed what our 'focal length' may be. The important thing to us, is the f-number, and its merely worth observing that many 'zoom' lenses change f-number when you zoom... the f-number tending to get higher, begging a slower shutter-speed to maintain the same 'exposure'.

Next I mentioned how far the 'sensor' or focal plane in my camera was from the lens-mount, about 45mm-ish. This 'gap' is there to to accommodate the 'mirror' for the view-finder that lets me look through the same lens as takes the photo. And it needs that 'space' so that it can hinge 'up' out of the way, to let light fro the lens get to the sensor when I press the shutter.. so you cant really stick a bit of class in it's way... that means, you cant 'physically' put a lens of 'true' focal length less than 45mm-ish on the camera... well you could... but it wouldn't be focusing on the sensor, cos it would HAVE to be more than 45mm away!

Consequently, almost all SLR camera lenses are what is know as 'Retro-Focus', and this accounts for some of those 'extra' lens elements in their construction. They are used to 're-focus' the image the lens captures, and chuck it 'back' the depth of the mirror housing.

Not particularly 'relevant' to very much, but, on the principle that every extra bit of glass you pass light through is a chance for more image degradation, light-loss and distortion, the 'less' elements a lens had, the better, so having perhaps two or three extra elements just to 'compensate' for having a mirror in the way of the lens, was good cause for many serious photographers of old to spurn 'SLR' cameras with a mirror in the way, in favour of separate view-finder, 'Range-Finder' or Twin-Lens-Reflex cameras, without them.. as well as 'zoom' lenses that usually have extra elements to move around and get the different 'equivalent' focal lengths in the range the zoom offers, i favour of 'fixed' focal length 'prime' lenses.

Curiously, this little bit of 'lore' is something that could be sung of in favour of 'mirror-less' system cameras, and I wish to mention only to tell them to STOP buying up all the lovely old 35mm SLR film camera lenses I'd like, for them! You are buying 'extra' distortion to 'correct' for a problem you dot have, and probably introducing even more, adding an adaptor mount with yet another element in it! Stick to your own system's lenses! Leave the old filmie ones to us old filmies! Expensive enough we have to pay for film, without compete with you lot for shorter focal length lenses for them! And if you really want to get 'shallow DoF' effects, you don't 'need' 'fast' f2, f1.8 or f1.4 prime lenses, you need a bigga-sensa! (Like, maybe 4.5cm or so ;-))
 
:)Thanks, yes as a beginner I'm still learning the basics I appreciate people's comments and advice and yeah it is confusing :confused:
 
Suvv said:
I do not wish to confuse you, or be too pedantic, but where people have used the term Depth of Focus it should really have been Depth of Field. This may save you getting confused at the workshop.
I may seem to be nit-picking but Depth of Focus is actually used for something different (all to do with the image being created at the sensor and not particularly interesting or useful at this point).
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Correct. Depth of Focus and Depth of Field are entirely separate from each other and refer to very different things.
 
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accidental double post
 
UaeExile said:
It's actually very simple. Not that you'd think it looking at some of these posts!
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I know. People tend use these threads to basically show off how much they know... not to help people. A beginner needs to just understand how the aperture affects the image and the exposure. That way they can start using it and see the results for themselves.
 
ImageUploadedByTalk Photography Forums1453023112.274785.jpg
 
The exposure triangle (which I don't think has been mentioned here - but I haven't read all those very loooonnngggg posts) is probably the most difficult part of photographic theory to understand to beginners.

Easy to remember though is this:

Small number = big hole = less in focus (shallow depth of field)
Large number = small hole = more in focus (deeper depth of field)

The depth of field thing changes with the focal length of the lens, distance from the subject, and even the type of camera; but I would focus on the phrase above to get to grips with it. Just remember, that if you change your aperture, it will let more or less light in, so given that your exposure is already correct, you will need to change something else to keep the amount of light equal.

The reason you may want to change the aperture (given the exposure is correct) is for reasons such as:

Making the subject stand out from a blurred background (big hole) - very often done with wildlife.
Getting the foreground and the distance both in focus (smaller hole) - common technique for landscape images.

Hope that helps.
 
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