Basic question: Difference between f5.6 and f2.8 and ISO


maisatomai

Deregistered
Oct 26, 2006
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#1
Just wondering if I use a 400mm f5.6 and get a ISO of 1600. If I use a 400mm f2.8, what ISO will I get? I tried googling but they don't seem to give exact relationship.
 

kennykck

New Member
Jan 3, 2011
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#2
The wonder of DSLR is the ability to set the setting MANUALLY according to situation. ISO is the sensitivity of the sensor and it is independant variable.
 

kei1309

Senior Member
Apr 12, 2010
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#4
your question has nothing to do with focal length.

you should take it out of the equation.

if you don't understand what ISO, Shutter Speed and Aperture do, and how they function, no matter how much we explain to you, you'll never get it.

go wiki ;)
 

maisatomai

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Oct 26, 2006
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#6
Holding everything constant? For example if I shoot at a point using 400mm f5.6, I get ISO 1600 when using aperture of f5.6. When I shoot at the same point using 400mm f2.8, will I get ISO 400 when using aperture of 2.8 (because of the 2 stops difference?)
 

Rashkae

Senior Member
Nov 28, 2005
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#7
Holding everything constant? For example if I shoot at a point using 400mm f5.6, I get ISO 1600 when using aperture of f5.6. When I shoot at the same point using 400mm f2.8, will I get ISO 400 when using aperture of 2.8 (because of the 2 stops difference?)
You know, you could always just test it and see...
 

maisatomai

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Oct 26, 2006
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#8
The problem is I do not own a 400mm f2.8.
 

kei1309

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Apr 12, 2010
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#9
Auto ISO?

all things constant... not really. you didn't state the shutter speed. if your shutter speed stays the same, then yes,your ISO will be 400
 

kelchew

New Member
Feb 25, 2011
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bedok
#11
sorry ts for asking here
can i ask abit ISO, it "stop" count is it in this way?
100, 200, 400, 800, 1600, 3200, 6400, 12400

should i use on this few stop or can i use some in between? etc 640?
 

Rashkae

Senior Member
Nov 28, 2005
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#12
sorry ts for asking here
can i ask abit ISO, it "stop" count is it in this way?
100, 200, 400, 800, 1600, 3200, 6400, 12400

should i use on this few stop or can i use some in between? etc 640?
You can use whatever ISO is needed for your shot, and do not need to be limited to the full stops.
 

pinholecam

Moderator
Staff member
Jul 23, 2007
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#14
Just wondering if I use a 400mm f5.6 and get a ISO of 1600. If I use a 400mm f2.8, what ISO will I get? I tried googling but they don't seem to give exact relationship.
On the long term, it will be helpful if you read up on exposure.
For the short term, f5.6 down to f2.8 is 2 stops.
So from ISO1600 down 2 stops its 1600 > 800 > 400
As mentioned above, the easiest way is just to play with the settings with your camera and any lens that goes to f2.8.




sorry ts for asking here
can i ask abit ISO, it "stop" count is it in this way?
100, 200, 400, 800, 1600, 3200, 6400, 12400

should i use on this few stop or can i use some in between? etc 640?
You can set it in the camera to use 1 stop; 0.5 stop; 0.3 stop increments.
 

Last edited:

kelchew

New Member
Feb 25, 2011
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bedok
#15
You can set it in the camera to use 1 stop; 0.5 stop; 0.3 stop increments.[/QUOTE]

thanks didnt notice that can change.. think i didnt explore my cam enough.. :)
 

soeypixels

Senior Member
Jun 24, 2007
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#16
last time when pple learn to shoot with SLR.

they will use 1 paper with few columns to jot down Fstop, ISO, S.Speed for each of the image they took
they will mount a tripod, shoot the same images many times by vary the different 3 factors
i think newbies should do that, cos when i learn to shoot DSLR 5years back, my instructor insist all of us should shoot with film camera

pls go search bryan peterson in youtube
see all his videos from 1 - xXx
 

Last edited:

sfoto100

Senior Member
Nov 29, 2009
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#17
Holding everything constant? For example if I shoot at a point using 400mm f5.6, I get ISO 1600 when using aperture of f5.6. When I shoot at the same point using 400mm f2.8, will I get ISO 400 when using aperture of 2.8 (because of the 2 stops difference?)
if everything being constant, then yes, u r right. but it is not correct to say u will get iso 400, because either u set iso to 400 or u use auto iso and for auto iso, i am not sure if your camera will set it to iso400.

but exposure wise f2.8 with iso400 = f5.6 with iso 1600 when the shutter speed remains constant for both cases.
 

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