Depth of field advice req again

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steelcity65

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Could anyone please advise me on depth of field. I have a Sony A300 and am using the Sony 18-70 mm lens F2.4. I am setting my f stop to its lowest but still not getting the blurring effect i am after.All be it i have not printed any yet.
An example is whilst away at the weekend i had the person to the front and about 50 yards behind was a forrest i set the fstop to 2.4 thinking that should do it and the forrest is also in focus.
I also have a Tamron 70-300 F4 lens would this be better?

I am using it on auto foces cold this be the cause?
I am also just about to invest in the 50mm F1.4 Sony lens would this help?
Thanks Craig
 
Can you clarify the lens that you are using and the mode and focal length you are shooting?

I can't see a sony 18-70 f/2.4 lens. The Sony 18-70mm f3.5-5-5.6 D kit lens should still let you get narrow dof - certainly compared to a forest 50m away.

Could you post up an example pic and the exif data then we could maybe say what is going wrong. Are you sure you have the aperture set to the largest aperture (smallest number)? and not set to 22 or something?

You want the smallest aperture number - and you need to be sure that you are getting that - so no auto mode or anything. Auto Focus will be OK but not Auto or landscape mode or anything like that.

example pic with exif.


(yes a 1.4 will give you very narrow dof, but even with an olympus I can get narrow dof with 1.8/2.5 etc)
 
Check out this link, probably explains it best with images.

http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

cambridge in colour
Aperture and focal distance are the two main factors that determine how big the circle of confusion will be on your camera's sensor. Larger apertures (smaller F-stop number) and closer focal distances produce a shallower depth of field.
Click to expand...

Peter
 
that's a little bit ambiguous - but it means that being closer to the subject produces a narrower DoF, rather than smaller focal length lens (which actually needs quite the opposite).
 
Sorry it is the f3.5 lens i am at work at the moment so dont have examples available. Does the zoom length make a differance?
 
Yes, as James and Peter have shown above.

Also the kit lens is only 3.5 at the wide end - it is at best 5.6 at the long end so you have an impact from the lens characteristics.
 
for the type of photography you're attempting you really need a lens like the Canon 85mm f1.8 (sorry not familiar with the Sony equivalent).
 
Depth of field is changed by two things: the f/number, and the size of the image.

Lower f/numbers give less depth of field. You'll need something like f/2 to get really shallow depth of field, but you can still do it with f/4 or f/5.6.

A larger image gives less depth of field. If you move closer, the image of the subject gets bigger and depth of field is reduced. If you increase focal length, the image of the subject gets bigger and depth of field is reduced.

So, set your lens to its lowest f/number, focus on the shortest distance, and focal length to maximum. You now have minimum depth of field, probably only a few inches of sharp focus.
 
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