Understanding Aperture

As a very very basic explanation...

The F3.5 - 5.6 refers to the lowest the F number achievable at the different focal lengths.

so at the widest possible of 18mm the lens can achieve an aperture of 3.6 however once you move that to 55mm the lens can't achieve that same low aperture with the number only being able to got as low as 5.6.

I'm sure most of the guys on here will be able to give a more technical explanation if you want it but that knowledge is as far as I can go.

Hope that helps
 
As above, the 3.5-5.6 is the lowest is can go at the widest and longest end of the lens zoom. It can of course go higher, its not limited to 3.5-5.6.
At 18mm, you could go up to f/22 (dont!), as you could at 55mm (again, dont)

However at 18mm, the aperture can go down low to 3.5, but as you zoom, the lens will close down to 5.6.
 
The F3.5 - 5.6 is the largest aperture the lens can achieve. ( aperture values can be slightly confusing; the smaller the number, the larger the aperture) F3.5 is the max aperture at 18mm and f5.6 is the max aperture at 55mm

It's a bit like talking about a car engine and saying it's 2 litre, max power 150 horse power. You aren't always going to be using the maximum power.

The f9 and f11 values are the required apertures for the light levels, shutter speed and ISO you had at the time.

The change in aperture as you zoomed out was probably due to more sky being included the wider shot
 
TCR4x4 said:
As above, the 3.5-5.6 is the lowest is can go at the widest and longest end of the lens zoom. It can of course go higher, its not limited to 3.5-5.6.
At 18mm, you could go up to f/22 (dont!), as you could at 55mm (again, dont)

However at 18mm, the aperture can go down low to 3.5, but as you zoom, the lens will close down to 5.6.
Click to expand...

As I'm a novice can you please explain why you say don't set to f/22

To be honest I do not even know how to manually set camara to f/22
 
You shouldnt set your aperture to f/22 because whilst the Depth of Feild (area that is in focus from front to back) will increase, you will actually end up with quite a soft image due to diffraction.

You will start to see diffraction at around f13 or f16 (it get worse the higher the f-number is). In general lenses are sharpest around f8.

Try to learn and understand how to use your camera in the most basic sense. Switching to AV mode is a good way of learning what aperture does!
 
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Fla5h said:
As I'm a novice can you please explain why you say don't set to f/22

To be honest I do not even know how to manually set camara to f/22
Click to expand...

See above :thumbs:
 
I've just taken 2 photos of the same object but different apertures

IMAGE1
f4.5 1/60 sec ISO-400 34mm
http://lightbox.com/photo/o9XveyA

IMAGE2
f/22 1/20 sec ISO-3200 34mm
http://lightbox.com/photo/cGO1Cab

Sorry couldn't help but doing the 'Don't f/22'

The main difference to me is that the background is blurred on IMAGE1 which is set to f/4.5 compared to IMAGE2 where the the aperture is set to f/22

Apart from that I'm still stuck as to why not use f/22
 
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Fla5h said:
I've just taken 2 photos of the same object but different apertures

IMAGE1
f4.5 1/60 sec ISO-400 34mm
http://lightbox.com/photo/o9XveyA

IMAGE2
f/22 1/20 sec ISO-3200 34mm
http://lightbox.com/photo/cGO1Cab

Sorry couldn't help but doing the 'Don't f/22'

The main difference to me is that the background is blurred on IMAGE1 which is set to f/4.5 compared to IMAGE2 where the the aperture is set to f/22

Apart from that I'm still stuck as to why not use f/22
Click to expand...


Its very technical and not worth worrying about yet.
In simple terms, it makes images look blury and out of focus.

Once youve been shooting for a while, you will start to notice things like this, until then, just keep shooting and practicing.
The only time you would usually use f/22 on a crop camera is on a macro lens where you need huge DOF.
 
aperture is consistent with depth of field requirements
your lens opening up to its maximum lets you use a fast speed where dof isnt a major consideration
when it is you have to select an aperture which suits the situation and then the speed to satisfy the exposure value...going up an iso will help if your speed is too low for hand held , or use a tripod
always go for the largest aperture suitable...so you dont waste dof on a subject which doesnt merit it and so get the speeds high
you cant really tell...unless its a racing car...what speed was used on a really sharp shot...but you can if its showing camera shake
setting your camera on programme will choose speed and aperture for focal length being used and tend to harmonise the settings with speed not being taken as a priority
whew!
cheers
geof
 
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