depth of field and f-number


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Phygee

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May 7, 2008
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#1
hello! obviously a newbie here....that's why i'm posting on the newbies corner.....:)

i'm currently using a second hand 400D body (which i bought from a nice bro from this Club) and some old lens salvaged from my dad's
90s SLR... not fancy and i guess it's a modest but prudent start.

i've been reading the newbie threads and stickies and was wondering if anyone can help me with some questions regarding this depth of field button located near the lens mount and the f-numbers stated on the lens.

I understand that a small f-number (of course combined with numberous other factors) would result in bringing depth in a close up shot of an featured subject and you'll get depth with a smaller f-number. Question is : if it is stated on your lens that the f range is say for e.g. 4.5 to 6.5, does that mean that you will not be able to adjust the number lower than that? And how does the depth of field button help? :confused:
 

Gengh

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May 6, 2007
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#2
Hope I understood your question correctly. I suppose you're using a zoom lens, where an f-number range is stated. Using the example of a generic kit lens, 18-55mm, f3.5-f5.6, it means that:
@18mm, the smallest f-number you can use is f3.5
@55mm, the smallest f-number you can use is f5.6

You can't adjust the number lower than those.

When you look through the viewfinder, you're looking at the scene at the smallest f-number your lens allows, regardless of the setting on your camera body. This also means that you're seeing the scene with less depth of field than your f-number setting would provide. Pressing the depth of field button stops the lens down to the f-number that you have set, so that you can see the actual depth of field according to your setting. But the viewfinder would look darker, especially if you're using a large f-number.
 

night86mare

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Aug 25, 2006
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#3
i've been reading the newbie threads and stickies and was wondering if anyone can help me with some questions regarding this depth of field button located near the lens mount and the f-numbers stated on the lens.

I understand that a small f-number (of course combined with numberous other factors) would result in bringing depth in a close up shot of an featured subject and you'll get depth with a smaller f-number. Question is : if it is stated on your lens that the f range is say for e.g. 4.5 to 6.5, does that mean that you will not be able to adjust the number lower than that? And how does the depth of field button help? :confused:
depth of field preview can USUALLY be customised to either:
1) give you a digital preview of the scene you are shooting, which is rubbish, you might as well shoot the picture
2) this one's more useful, it makes the lens "stop down" so that you can see the exact depth of field you are getting. can be used for:

a) seeing where your graduated neutral density filter horizon line is, because it generally darkens the scene in your viewfinder. google what gnd filters are if you don't get this.
b) obviously, seeing depth of field. please focus if you want to see what you will get. but this doesn't actually mean that you will get what you see through the viewfinder, because people move, hands shake, etc.

i am not sure what you are talking about in your second paragraph; but in summary, large f/stop number = small aperture = large depth of field. small f/stop number = larger aperture = shallow depth of field. for portraits, usually large apertures are used. for landscapes, usually f/8 and bigger f/stop numbers are used.

usually lenses come affixed with maximum apertures that they can do. this is because there is an obsession with the consumer market about fast lenses, which not everyone needs, but everyone wants. i wonder why there isn't the minimum aperture that it can go, i mean, with f/55 or so you might get very pretty little starburst effects.. :bsmilie:
 

yehosaphat

Senior Member
Oct 28, 2005
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#4
Bit confusing in your description here. Some impt concepts here:

#1
f-number determines the size of your aperture which directly determines your DOF.

#2
The smaller your f-number, the larger your aperture and the smaller your DOF. So, the larger your f-number, the smaller your aperture and the larger your DOF.

#3
The smaller your DOF, the smaller the area your subject will be in focus. You get a blurred background as a result. This is what we call bokeh.

#4
For f stops that come with a range liek 4.5-5.6. It means the maximum aperture your lens can open is at f4.5 at your shortest end and f5.6 at your longest end.
 

calebk

Senior Member
Jul 25, 2006
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Clementi
#5
...
I understand that a small f-number (of course combined with numberous other factors) would result in bringing depth in a close up shot of an featured subject and you'll get depth with a smaller f-number....
Um...you seem to be going round in circles.

A small f/stop value gives a shallow depth of field
A large f/stop value gives a deep depth of field.

You seem to be confused also, in saying a small f/stop value brings depth (don't quite get your use of terminology - get depth and brings depth :dunno: )
 

Phygee

New Member
May 7, 2008
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#6
Um...you seem to be going round in circles.

A small f/stop value gives a shallow depth of field
A large f/stop value gives a deep depth of field.

You seem to be confused also, in saying a small f/stop value brings depth (don't quite get your use of terminology - get depth and brings depth :dunno: )

:confused: Newbie mah.....dat's why confused! :confused:
 

Phygee

New Member
May 7, 2008
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#7
:thumbsup: Thanks bros.... for taking time to reply to my post! :thumbsup: Really appreciate it! :gbounce:
 

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