Shallow DOF


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dorts

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Mar 10, 2007
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#4
Distance affects the DOF too. :)
 

KangS

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Sep 15, 2005
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#5
Generally, the smaller the f-stop number, the shallower the DOF for a given distance to object. ;)
 

zac08

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Feb 21, 2005
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#7
smaller aperture value:)
Eh.... you have to be careful with such phrasing, else they may mistake using f11 or f16 as a smaller aperture value.

A large aperture in correlation to the lens focal length will give you a nicer blur of the background as well as foreground. Often it will mean as big as f1.4 to f1.8 for a short focal length of 50mm. As the focal length increases, you can use smaller apertures such as f5.6 or f8 to the same effect.
 

dorts

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#9
Small aperture means a F stop of like f/22 which means deeper DOF. Large aperture means a F stop of maybe f/2 which will give you your shallow DOF. :)
 

Antzzz

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Apr 28, 2007
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#10
Depth of field formulae

Hyperfocal Distance
Let f be the lens focal length, N be the lens f-number, and c be the circle of confusion for a given image format. The hyperfocal distance H is given by
H=f2/Nc

Moderate-to-large distances
Let s be the distance at which the camera is focused (the “subject distance”). When s is large in comparison with the lens focal length, the distance DN from the camera to the near limit of DOF and the distance DF from the camera to the far limit of DOF are
Dn=Hs/(H+s), Ds=Hs/(H-s)

When the subject distance is the hyperfocal distance,
Df=infinity, Dn=H/2

The depth of field Df − Dn is DOF=2Hs2/(H2-s2), etc...

Confused now? haha, just wiki DOF lah. If not go riceball to buy a few good books for your bedtime reading. Cheers :cheers:
 

zac08

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Feb 21, 2005
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#12
i actually don't know when to use what fstop with what focal length to achieve best results.
The largest aperture you can get away with to maintain DOF in your shots....
 

lsisaxon

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Nov 29, 2004
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#14
Eh.... you have to be careful with such phrasing, else they may mistake using f11 or f16 as a smaller aperture value.

A large aperture in correlation to the lens focal length will give you a nicer blur of the background as well as foreground. Often it will mean as big as f1.4 to f1.8 for a short focal length of 50mm. As the focal length increases, you can use smaller apertures such as f5.6 or f8 to the same effect.
Aiyah.. you also not exactly right.. f-number is a reciprocal.. so the number is at the denominator. f/1.4 or f/11. f refers to the focal length. ;p So the bigger the denominator, the smaller the aperture and vice versa. It's just Maths.
 

zac08

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Feb 21, 2005
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#15
Aiyah.. you also not exactly right.. f-number is a reciprocal.. so the number is at the denominator. f/1.4 or f/11. f refers to the focal length. ;p So the bigger the denominator, the smaller the aperture and vice versa. It's just Maths.
I know... but I was hoping to reduce the confusion
 

zcf

Senior Member
Apr 10, 2005
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#17
it actually depend on both combination :sweat:

focal length
18mm----300mm
large------small DOF

f/16------f/1.4
large-----small DOF

So a 300mm lens at f/1.4 :)bigeyes:) will give you very very narrow depth of field.
a 18mm lens at f/16 will give you large depth of field, which mean most thing will be in focus.

Still got another influence, depend on how close is the focus subject toward the lens, the closer the subject the shallower DOF.
e.g.
a subject shoot by 50mm lens f/5.6.
further---------closer
large---------small DOF

you can use the DOF calculator at the link to simulate the situation you want.
http://www.dofmaster.com/dofjs.html
 

boredphuck

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Aug 24, 2007
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#18
tat whats wad i meant. a f/5 on 2 different focal length will give very different results. i'm using a pns. no wonder i have to stick my face into the object to get a good narrow dof.
 

KangS

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Sep 15, 2005
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#19
tat whats wad i meant. a f/5 on 2 different focal length will give very different results. i'm using a pns. no wonder i have to stick my face into the object to get a good narrow dof.
Its 'shallow', not 'narrow' ... DOF as the name implies is 'depth' how far into a picture is an object in focus. Not how far away from the centre of a view that its in focus.

Some picts of focusing off-centre and on-centre for comparison might make a better point.

Generally P&S can take pretty good shallow DOF pictures but only at Macro level. once you get big objects, even with a f2.8 aperture, its quite hopeless unless its some very brightly conditions. I tried with my prosumer camera, never could get it to work well with objects bigger than a pail! :hung:
 

ortega

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Staff member
Nov 2, 2004
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#20
in order to get a shallower DOF on your lens

• zoom to the longest focal lenght
• use the biggest aperture you have
• position subject further away from the BG
• position subject closer to the camera
 

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