DOF

D.S.

D.S.

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Yes
Depth of field.

Ok sorry for the real numpty question :bonk:

When I hear lots of talk about DOF what's it actually referring to?

The depth eg distance of the 'in focus' bit of the photo?

Here's how my minds thinking (its a weird place my mind)

Thinking of an image as a sliced loaf of bread, you the tog is stood at the crust on one end, you focus on a point say 8 slices in and snap your picture. Looking at the image afterwards you can see that although you focused on slice 8, slices 7, 9, 10 & 11 are in focus too. So is this a wide depth of field? So you swap lens and again take a shot of slice 8. Looking at the picture this time you notice only slice 8 is in focus. Is this a narrow depth of field?

So what causes this, and how can the tog control it?

I have noticed on my D60 18 55 kit lens I seem to get a very narrow depth, when id like to see more. An example I took a shot of a walkers sign post saying so and so that direction >, I had the camera close to the post and was shooting away, down the direction of the sign. When looking at the pictures afterwards I found only one letter was in focus. I tried changing focal points but all this did was bring a different letter into focus, when I wanted all the letters sharp. :bang:

Sorry if this is in the wrong place, mods please move if necessary.

Many thanks!
 
Have a look at this

http://www.mir.SPAM/rb/photography/fototech/htmls/depth.html
 
Someone will come and give you an in depth technical explaination on this shortly no doubt but the short version is:

1) Your analogy is correct.
2) It's controlled by a combination of aperture and distance to subject. A wide aperture (2.8 for example) will give shallow depth of field whereas a narrow one (f11) will give greater DOF.

At greater distances the relative distance between the camera and the subject means that the effect of wider apertures will be lessened. I.e. Shooting at 2.8 at a close subject will produce a more shallow perceptable depth of field than say the same settings snapping a subject at 100 metres away.

Clear as mud? :gag:
 
yep thats it :D and i can see my mud clearly on my car as well :lol:
 
A good guide is that wherever the point of focus is The depth of field will have its area split. This means that 1/3 of the DOF will be closer to the point of focus than the camera and 2/3 of the DOF will be beyond the point of focus. Hope that makes sense.

This is why in landscape photography they recommend you focus on a point 1/3 of the way into the scene to ensure everything is in focus.

With a macro lens the split is 50/50.
 
even with a aperture of 2.8 i still cant achieve blurred backgrounds ??

is there anything else i need to do please
 
Are you actually using the lens at f2.8, if you're in P mode it wont be at f2.8 you would need to set it to aperture priority with the aperture set to f2.8.

Aside from that get close to the subject with the background far away that increased the background blurring.
 
yes, Aperture at 2.8

will the shutter speed affect this?
 
Best bet would be to post some examples so that we can see why my might possibly be getting a fairly large dof at f2.8.
 
thanks for the help:)

i had a play last night....
and FINALLY Got what i was after... main subject in focus, background blurred.

got close to the subject, had to use manual focus, but then press the auto focus button and wahey! :D
just need to try it outdoors now
 
All the answers above are right (more or less) :-)

In fact, it isn't the f/number that matters, it's the lens aperture. f/number is just a mathmatical calculation and it works like this.
Take the focal length of the lens (F) and divide the actual (or effective aperture in Americanese) , let's say f/10. 100/10=10 the so f/number is f/10.
Another one. F25/10=2.5, so f/2.5

So, with a 100mm lens (F100), a 10mm actual aperture on a 100mm lens produces f/10, with a 25mm lens the same actual aperture is only f2.5. Both produce exactly the same depth of field. This explains why the depth of field at (say) f/2.8 on a point & shoot digi with a F10 lens is much greater than on a larger camera with a longer focal length lens. It's also the reason that P&S cameras don't have the option of small apertures, it would be difficult to make them adjust that small and would cause image quality problems even if it could be done. It also explains why the depth of field of, say, a batsman hitting a ball taken from a very long way away with a 300mm lens at f/2.8 is so limited - divide 300/2.8 and you'll see that the actual aperture is a massive 107mm!
 
subseasniper said:
A good guide is that wherever the point of focus is The depth of field will have its area split. This means that 1/3 of the DOF will be closer to the point of focus than the camera and 2/3 of the DOF will be beyond the point of focus. Hope that makes sense.

This is why in landscape photography they recommend you focus on a point 1/3 of the way into the scene to ensure everything is in focus.

With a macro lens the split is 50/50.
Click to expand...
This is rubbish, by the way. I have no idea where the 1/3 - 2/3 rule come from, but in most situations it is not applicable.
 
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