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ISO question

Huggy Bear · 2007-01-30 09:41:46

Hi all, I've a question (sorry if this is a bit of a Homer Simpson, "Duh" question!!) on ISO that I was hoping someone would be able to answer ... I was reading a magazine article on lens recently and the article mentioned that "a lens set to f5.6 @ 400 iso would be equivalent to f2.8 @ iso 100". ok, I understand the…

30-01-2007 9:41am

#1

Huggy Bear

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Hi all,
I've a question (sorry if this is a bit of a Homer Simpson, "Duh" question!!) on ISO that I was hoping someone would be able to answer ...
I was reading a magazine article on lens recently and the article mentioned that "a lens set to f5.6 @ 400 iso would be equivalent to f2.8 @ iso 100".
ok, I understand the app\shutter exposure balance and that ISO defines the quantity of light hitting the sensor, thus a higher ISO will increase the f-stop options and that the consequence is noise ... so I'm questioning the articles comments, as f5.6 will not give you the same DOF as f2.8? or am I misreading the quote or phrase "equivalent" in the article, as regardless of ISO DOF at f5.6 is not the same as f2.8?
I suppose my question is can ISO change the DOF? I didn't think so ...
or is it that the amount of light is a balance between ISO/App/Shutter but DOF is only related to aperture, which is my understanding ...
Cheers
HB

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#2 30-01-2007 9:45am

magicbastarder

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all they meant was that the exposure was equivalent, not DOF.

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#3 30-01-2007 9:55am

Valentia

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Huggy Bear wrote:

the article mentioned that "a lens set to f5.6 @ 400 iso would be equivalent to f2.8 @ iso 100".

That's only true if the shutter speed is the same.

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#4 30-01-2007 9:57am

Huggy Bear

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cheers, I'm new to photography only at it a year or so, so I get "jumpy" when I read or in this case "mssread" articles that go against what I thought I knew was happening

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#5 30-01-2007 10:38am

TelePaul

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What's noise? Graininess?

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#6 30-01-2007 10:43am

Huggy Bear

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Yep: little article here ... I'm sure there's better explainations out there ... but this one is alright.

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#7 30-01-2007 11:12am

B0rG

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well, in a way, ISO may indirectly affect the DOF, because you will have to change the apperture. There is no direct effect.

DOF is a function of focal length and apperture, yes.

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#8 30-01-2007 12:16pm

magicbastarder

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isn't it the case that actual DOF is not a function of focal length, only apparent DOF?
well, ii once read that but never gave it any further thought.

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#9 30-01-2007 1:39pm

B0rG

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this may clear it up a little bit:

DOF chart for 17-40
http://www.canon.com/camera-museum/camera/lens/ef/data/ef_17~40_4l_usm_dof.html

my thread about dof and stuff, if you don't mind my arrogant tone.
http://www.boards.ie/vbulletin/showthread.php?t=2055017723&referrerid=&highlight=

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#10 30-01-2007 1:48pm

mikeanywhere

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B0rG wrote:

if you don't mind my arrogant tone

Now, I would never have said that about you my foreign friend!!

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#11 30-01-2007 1:50pm

magicbastarder

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that (on a cursory inspection) seems to confirm what i thought - that wide angles give you better depth of field due to out of focus objects being 'rendered' smaller in the frame, and counteracting the lack of focus. if you follow me.

edit: reading further...

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#12 30-01-2007 2:04pm

B0rG

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mikeanywhere wrote:

Now, I would never have said that about you my foreign friend!!

good
:-|

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