ISO vs Aperture? Which is more important?


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maisatomai

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Oct 26, 2006
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#1
When taking photo with my 400d, I am confused whether to choose ISO 100 and 3.5 aperture opening or ISO 400 and a 16 aperture opening (for example). Which one is more important? As for shutter speed? Is 1/60 enough to take a totally blur-free photo?
 

ziploc

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Jan 17, 2002
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#2
Eh, both are important. :bsmilie:

It all depends on what you want to achieve actally. I would use aperture setting to control the DOF to achieve the effects I needed. If while doing that, the shutter speed drops too low and I need to do it hand held then I would bump up the ISO.

For shutter speed, the rule of thumb is 1/focal length. So if you're shooting at 200mm with 1.5x crop factor, you would need a min shutter speed of 1/300s to avoid camera shake. Of course if you have VR/OS or a pair of super steady hands then you could go with slower shutter speed.
 

Snoweagle

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#3
When taking photo with my 400d, I am confused whether to choose ISO 100 and 3.5 aperture opening or ISO 400 and a 16 aperture opening (for example). Which one is more important? As for shutter speed? Is 1/60 enough to take a totally blur-free photo?
For me, i adjust ISO according to lighting condition and aperture according to the situation itself. 1/60 depends on what lens u're using, what focal length u're taking at and handholding technique.

Example, if u're using a UWA such as the EF-S 10-22, 1/60 is enough at either ends. If u're suing a tele like 70-200, then it's not enough unless with the help of IS. In general, to obtain a steady shot will be 1/focal length (35mm equivalent).
 

ijnek

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#4
high iso will gain more noise which gives a gainy effect....
this might be useful if u r tryin to create a gainy effect.......
 

ziploc

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#7
Hi maisatomai,

Here is how you could approach your shooting:

Aperture priority mode:
1. Select the aperture that would satisfy the DOF that you require.
2. Look at the focal length and see if the shutter speed is at least 1/focal length (remember to factor in your crop factor).
3. If the shutter speed is too low, bump up the ISO.
4. If the ISO need is getting too high (which introduce noise), or not able to make the shot, either select a wider aperture or use flash.

Shutter priority mode:
1. Select the shutter speed that would satisfy you requirement. Remember that you might need to use a tripod/monopod if the shutter speed needed is below 1/focal length.
2. Look at the aperture selected by the camera to see if it is adequate.
3. If the aperture is not adequate, adjust the ISO to compensate.
4. If the ISO need is getting too high, or not able to make the shot, either select a slower shutter speed or use flash.
 

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Octarine

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Jan 3, 2008
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#8
When taking photo with my 400d, I am confused whether to choose ISO 100 and 3.5 aperture opening or ISO 400 and a 16 aperture opening (for example). Which one is more important? As for shutter speed? Is 1/60 enough to take a totally blur-free photo?
Do you know what is the difference of using f/3.5 and f/16? Ever heard of Depth of Field? Define what is the leading parameter of your "exposure equation": Aperture for controlled DOF? Shutter speed to freeze motion? Low ISO for noise-free images? Depending on the answers you select the respective mode in your camera and adjust the primary parameter. Then you'll see where the other parameter will end up, given your predefined ISO. if it works, then fine, go and shoot. If not, then your cam will tell you (e.g. blinking values in viewfinder) or you will see the 2nd parameter in an unsuitable range and you need to adjust or compromise.
Important is that you know about the base parameter for exposure and the relationship between them as well the effects to the image. The guideline 1/focal length has been mentioned already. But this only works for daylight and handhold!
 

Blur Shadow

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Sep 17, 2005
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#9
Aperture controls Depth of Field.
ISO controls sensitivity of your sensor.

You shall need to let your creativity decide what you need. If not, just shoot P mode. Less of a hindrance.
 

Aug 1, 2009
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#11
In a nutshell.


Aperture controls the depth of field.
ISO controls "sensor sensitivity to light".


In a nutshell,

If you want to make a shot with an Aperture setting but your shutterspeed is too low to get proper exposure, increase your ISO to speed up your shutterspeed. How much you want to compensate depends on your preference. Higher ISO = more noise.
 

lynxiger

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Sep 11, 2006
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#12
In short, creative and great shots are done with just the right aperture and ISO sensitivity. :)

I favor in choosing a good aperture depending on the subject, so I shoot mostly in A-mode. If the shutter becomes too slow, I'll boost the ISO.
 

catchlights

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#13
When taking photo with my 400d, I am confused whether to choose ISO 100 and 3.5 aperture opening or ISO 400 and a 16 aperture opening (for example). Which one is more important? As for shutter speed? Is 1/60 enough to take a totally blur-free photo?
ISO 100 and 3.5 aperture opening or ISO 400 and a 16 aperture is not the same value, more then two stops away.

most people can handheld shooting a wide angle focal length at 1/60, but not able to do so at tele angle focal length, for preventing hand shake problem, a common guideline is using shutter speed = 1/focal length, with proper handheld technique.

go and read the book by Bryan Peterson, understanding Exposure, you will understand better and systematically after you finish the whole book, rather than piece together all the information gathering here and there.
 

kklee

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Aug 13, 2004
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#14
When taking photo with my 400d, I am confused whether to choose ISO 100 and 3.5 aperture opening or ISO 400 and a 16 aperture opening (for example). Which one is more important? As for shutter speed? Is 1/60 enough to take a totally blur-free photo?
Sometimes it depends on the lens too. If let's say an all-around sharp image is required and setting to f8 or f16 will yield a sharper image compared with f3.5, I will choose to increase ISO to allow for that. Similarly, a larger aperture of f3.5 might cause more darkening at the edges, so having a smaller aperture might eliminate that thus ISO needs to be increased.
 

Snoweagle

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Jan 26, 2005
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#16
Yup, I do realize that. I'm just suggesting that TS can let the camera decide by selecting P mode, if all he wants is the correct exposure.
Yes i agree with that. Even the green box auto mode can do it too. But then what i feel is that if u buy a DSLR just to use in auto mode then defeats the purpose already.
 

spheredome

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Jul 5, 2007
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#17
Do the following in your own free time in addition to the knowledge others provided.

- take identical shots at iso 100, 200, 400, 800, 1600. Both day and low light and see their difference, learn the acceptable range of your camera to you (at resized view). See the difference between jpg and raw.

- Mount camera on tripod and macro photograph a small object (ruler, watch etc) at various f-stop (skip a few stops). See and appreciate the DOF difference. Do blow up the detail from F11 onwards and see the diffraction (soften in detail).

- Shutter speed appreciation, you figure that out.

Objective. To get a glimpse what they look like to feel the effect.

When taking photo with my 400d, I am confused whether to choose ISO 100 and 3.5 aperture opening or ISO 400 and a 16 aperture opening (for example). Which one is more important? As for shutter speed? Is 1/60 enough to take a totally blur-free photo?
 

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