cant get my head around aperture

Robbo

Robbo

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Right, I have read up and googled countless times and still dont get it,

All i want is a simple dumb persons explanation lol

i understand a big F. eg 32 will only open the shutter a small amount, while 2.8 would be its biggest. Ive read it as e.g. F 5 would be opening 1/5 th of the overall diameter?

so.....how does a small F number give shallow DOF if its opening up more to let more light into the camer, while a higher f. will make more of the picture in focus oven though it opens up smaller?
:bonk:
 
I read lots of websites and pretty much had it sorted in my head but purchasing 'understanding exposire' by Brian Peterson completely cemented it in.

Well worth buying it, his teaching methods seem to get subjects accross clearly without too
much jargon.
 
Robbo said:
Right, I have read up and googled countless times and still dont get it,

All i want is a simple dumb persons explanation lol

i understand a big F. eg 32 will only open the shutter a small amount, while 2.8 would be its biggest.
:bonk:
Click to expand...

the f stop has nothing to do with opening the shutter,,, two different things .
 
The aperture is best thought of as a lens function while the shutter is in the camera. (At least it was in the days of film (and yes I know some had shutters in the lenses but I'm being straight forward here OK?) and it does makes it simpler to understand if you separate the two)

The way I remembered it when I was trying to get my head round it was simply

Big number= small hole = big depth of field

and conversely

small number = big hole = small depth of field.

Totally over simplified but not a million miles from how it works. :)
 
the F number s in fractions so the bigger the number, the smaller the hole.

if you have a small F number eg 2.8 there will be a thin depth of feild (not a lot in focus) but the lens will be letting in a lot of light (faster shutter speed)

while a big F number eg 22 will be a small hole, this will give you a long depth of feild (lots in focus)

the apature controls how fast the light gets in the lens (like a egg timer, big hole goes through fast, small hole goes through slow)

hope that helps.....


...but it may just confuse you more
 
Experimenting with different aperture settings might be a good idea. The following examples of the effect of aperture settings might help.

f1.8
f18.jpg

f2.5
f25.jpg

f3.2
f32.jpg

f4
f4-1.jpg

f5.6
f56.jpg

f8
f8.jpg
 
dan_yorkshire said:
I read lots of websites and pretty much had it sorted in my head but purchasing 'understanding exposire' by Brian Peterson completely cemented it in.

Well worth buying it, his teaching methods seem to get subjects accross clearly without too
much jargon.
Click to expand...

I agree, this book really helped me, great purchase. Nice to look at now and again to get some inspiration too.
 
MagicMynx said:
http://www.elizabethannedesigns.com/living/2009/07/21/aperture-dun-dun-dun/

This diagram really helped me understand.
Click to expand...

Danger_Mouse said:
the F number s in fractions so the bigger the number, the smaller the hole.

if you have a small F number eg 2.8 there will be a thin depth of feild (not a lot in focus) but the lens will be letting in a lot of light (faster shutter speed)

while a big F number eg 22 will be a small hole, this will give you a long depth of feild (lots in focus)

the apature controls how fast the light gets in the lens (like a egg timer, big hole goes through fast, small hole goes through slow)

hope that helps.....


...but it may just confuse you more
Click to expand...

I was going to post up something similar but you beat me to it DM :thumbs:

...so, all I can comment on is the linky from MagicMynx and that it does provide a pretty good & simple take on this with some great example pics; especially the DOF ones with the gnome looking away whilst the bears are having a quick snog :p :D :lol:
 
When it comes to DOF, it's important to remember that it's not just aperture involved. Focal length and focus distance are just as important.

Three rules to making a shallow depth of field (doesn't have to be all three, but they all make a difference)...

Larger aperture
Longer focal length (i.e. longer lens or zoom in on a zoom lens)
Shorter focus distance (distance to the object)

And reverse for a deep depth of field.


If you want a perfect "everything in the image is sharp" image, then it's worth understanding Hyperfocal Distance. This is the sweet focus spot where you get the maximum depth of field.

We used to have guides on lenses which showed depth of field for an aperture and that made it easy to set the hyperfocal distance. Most modern lenses (Nikon at least) don't have these any more :(.

http://www.dofmaster.com/hyperfocal.html
 
MScotts said:
I was going to post up something similar but you beat me to it DM :thumbs:

...so, all I can comment on is the linky from MagicMynx and that it does provide a pretty good & simple take on this with some great example pics; especially the DOF ones with the gnome looking away whilst the bears are having a quick snog :p :D :lol:
Click to expand...

LOL glad you approve :thumbs: :lol:
 
Robbo said:
Right, I have read up and googled countless times and still dont get it,
All i want is a simple dumb persons explanation lol
i understand a big F. eg 32 will only open the shutter a small amount, while 2.8 would be its biggest. Ive read it as e.g. F 5 would be opening 1/5 th of the overall diameter?
so.....how does a small F number give shallow DOF if its opening up more to let more light into the camer, while a higher f. will make more of the picture in focus oven though it opens up smaller?
:bonk:
Click to expand...

f 32 opens the aperture..so do the others..the f no is related to area of opening
the links should explain all this.
the easiest way after you have read and still find it difficult to understand is just accept the phenomenon as an optical part of your cameras tools
use it and do some practice
if you know that f32 makes things in the shot more 'in focus..apparently'...then utilise it when you want that to happen
also wide open..f 2.8 'cuts down' on the depth of your focus range and you get a nice sharp image separated from background and foreground to suit that purpose

the tins of beans are a good example...do your own then you have hands on experience
but dont...!!!! take 57 shots
 
Robbo said:
Right, I have read up and googled countless times and still dont get it,

All i want is a simple dumb persons explanation lol

i understand a big F. eg 32 will only open the shutter a small amount, while 2.8 would be its biggest. Ive read it as e.g. F 5 would be opening 1/5 th of the overall diameter?

so.....how does a small F number give shallow DOF if its opening up more to let more light into the camer, while a higher f. will make more of the picture in focus oven though it opens up smaller?
:bonk:
Click to expand...

OK it seems as though you know that the aperture affects DoF but want to know how.

When your camera is focused on something, only that and things at the same distance from the camera are truly in focus.
Everything else is out of focus, some a lot, others a bit and some only a little - in fact some are out of focus by such a small amount that they seem to be in focus, this gives the DoF.

Now the bits that are out of focus have not focused as points on the sensor, they have reached the sensor as little circles (known as Circles of Confusion), if the little circles are small enough then we see them as points and they seem to be in focus.

A large aperture gives larger out of focus circles than a small aperture so with a small aperture more of things nearer and further than the focus distance will seem to be in focus.

Have a look here for diagrams etc http://www.cambridgeincolour.com/tutorials/depth-of-field.htm
 
A lot of the confusion surrounding apertures relates to the various terms used to describe them. They are often ambiguous, contradictory, and sometimes incorrectly mixed up.

The aperture is the size of the hole through which light passes to the sensor. The bigger the hole, the 'brighter' the light reaching the sensor and this is expressed as an f/number. Brighter apertures are known variously as larger, bigger, wider, faster, more open, lower f/number, smaller f/number.

At the opposite end of the scale, the smaller the hole, the the 'darker' the light. Darker apertures are known as smaller, slower, more closed, higher f/number, bigger f/number. Fun isn't it :)

The other thing is that the relationship between different f/numbers is not obvious. Although they are all linked by the halving/doubling principle that is obvious with shutter speeds and ISO (the other two factors affecting exposure) it is not immediately evident that, for example, f/4 is twice as bright as f/5.6. The key to this conundrum is that the square root of 2 is used, ie approximately 1.4, therefore 4 x 1.4 = 5.6.

The full range of apertures commonly used is f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22. Each one is either half or double the brightness of the number either side which explains why a shutter speed of 1/125sec at f/5.6 exposes the sensor to the same total amount of light as 1/250sec at f/4, or 1/500sec at f/2.8, and so on. You also hear intermediate f/numbers used, like f/3.5 or f/6.3, which can be used to mix and match with intermediate shutter speeds.

Furthermore, apertures and f/numbers are also known as 'stops' (historical term) and this term is now commonly used to refer to any halving or doubling of any aspect of exposure value, be it f/number, shutter speed or ISO setting. Technically that is wrong I guess, but it's been universally adopted.

There is no easy way around understanding all this jargon. You just have to learn it, but once you understand the principles you can usually make sense of it. For example, when you hear someone say open up a stop, or use a wider aperture, use a bigger aperture, use a smaller f/number, use a faster stop, use a lower f/number - all these mean (probably!) to use a brighter aperture.
 
found calling it depth of focus instead of field helped me
 
I spent an afternoon taking photos of one of my daughter's teddy bears, changing the aperture from 4 - 32 then the shutter speed from 1/1000 to 3", so I got used to the effects from both. It's an exercise that's worth repeating to get to know your camera :)
 
Eddie1 said:
found calling it depth of focus instead of field helped me
Click to expand...

It may have helped you, but is two entirely different things and may only serve to muddy the waters :nono:

Depth of field: is the amount of perceived focus in an image either side of the actual focus point (changes with aperture setting).

Depth of focus: Is the amount of leeway at the film/sensor plane, also known as the lens to film distance.
 
I think you may be getting bogged down in the technicalities, and early on in the learning process, which I feel can be a bad thing as it tends to totally confuse people and they give up. Well, don't give up!

I would suggest that you don't try to understand the science of it yet - just accept that:

A) Aperture is basically the size of the "hole" that the light travels through inside the lens

B) Altering this affects the exposure in a specific way and therefore the end result.

Then, as suggested, take some shots similar to the bean tins above, at various different apertures - put it on AV (or aperture priority) mode so the camera takes care of the shutterspeed for you - so all you need to adjust each shot is the aperture.

This will then help you to understand how it affects the exposure.

Once you have the basics as above firmly in your head, then you can worry about the science of it. Don't worry, it all seems a bit overwhelming to begin with but it will get easier and make more sense to you over time. After a while you will be shooting in full manual without even thinking about what settings to use, it will just come naturally.
 
Don't get bogged down by all this the first thing to do is realise that when you want to read something a long way away you tend to screw your eyes up therefore you tend to bring the out of focus object in focus. Well it's exactly the same with a camera lens. Take it by steps from there on.
 
Robbo said:
so.....how does a small F number give shallow DOF if its opening up more to let more light into the camer, while a higher f. will make more of the picture in focus oven though it opens up smaller?
Click to expand...

If you just consider one point of the subject you are photographing. Light from that point will hit every part of the lens from the centre right to the outside. The lens will try to converge those rays of light to a point of focus on the sensor or film which in theory will be the same point regardless of where the light entered and exited the lens. In practice, it's a bit of a compromise and whilst the lens will admirably gather all the light and place it in focus for objects which it is focused on, it will be a bit of a compromise for objects either side of that (closer or further away).

When you close the aperture down, you are limiting the amount of lens which can converge these rays of light, hence the reduction in light output, but you are also reducing the spread of focusing error. If you close the aperture down enough, you effectively have a pinhole lens - one which lets in hardly any light and focusses everything equally.

Not sure if that helped or made it more confusing though!


Steve.
 
the way I think about it is the aperture number divides the amount of light coming in.

so if you have loads of light then divide it by the f number. and the remainder is the amount of light that gets to the sensor.
so 1.8....1/f1.8...quite a lot still.
1/f22....not a lot of light left. Therefore you would need to increase the shutter time to allow more light in during the exposure.

you can then visualise how light is lost in longer zooms lenses....light would be lost in a long tube if you were looking down it.
it's not quite accurate but it might help
 
blue max said:
Though she does talk about "Then I stopped down all the way to f/4.0."

I always understood stopping down was the move to a larger f no. In my opinion she should be saying "Then I opened up all the way to f/4.0:

But maybe I'm wrong all these years!

Graham
Click to expand...

I think you're right Graham. You can hardly "stop all the way down to f/4". That is confusingly mixed up to the point of being wrong.

You could maybe "stop down to f/4" if you had a fast lens which could open up to a wide aperture with a very low f/number like f/1.4 but "all the way down" suggests the far end of the scale. Most people would understand that to be more like a very small aperture with a high f/number like f/16 or f/22. Just to mix up a few more terms :)

The description 'fast' in relation to low f/numbers is because they allow you to use a fast shutter speed, which is also known as a high shutter speed, which actually allows a low amount of light to fall on the sensor because it has a short duration. Doesn't get any less confusing does it? :lol:

The least ambiguous terms to use would be 'brighter' or 'darker' but nobody ever does.

Edit: while we're at it, depth of field means nothing to newcomers and depth of focus, which actually means something else, is often confused with it. The 'sharp zone' would be more obvious.
 
HoppyUK said:
I think you're right Graham. You can hardly "stop all the way down to f/4". That is confusingly mixed up to the point of being wrong.

You could maybe "stop down to f/4" if you had a fast lens which could open up to a wide aperture with a very low f/number like f/1.4 but "all the way down" suggests the far end of the scale. Most people would understand that to be more like a very small aperture with a high f/number like f/16 or f/22. Just to mix up a few more terms :)

The description 'fast' in relation to low f/numbers is because they allow you to use a fast shutter speed, which is also known as a high shutter speed, which actually allows a low amount of light to fall on the sensor because it has a short duration. Doesn't get any less confusing does it? :lol:

The least ambiguous terms to use would be 'brighter' or 'darker' but nobody ever does.

Edit: while we're at it, depth of field means nothing to newcomers and depth of focus, which actually means something else, is often confused with it. The 'sharp zone' would be more obvious.
Click to expand...

Thought I explained that in post 21 :p
 
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