# The Effects and Purpose of ISO and More!!



## DRB1313 (Sep 10, 2008)

I am going to attempt explaining ISO, it's use and the effects it has on our photos.

What is ISO?  ISO is basically the sensor's sensitivity to light.
The higher the number, the higher the sensitivity. ie: ISO100, 200, 400, 800, 1000, 1600.

What does this mean?  Simply this: The higher the ISO you have, the faster shutter speed you will be able to achieve.
Edit!! Additon-- It allows us to shoot in lower light situations.

Why is this important?  A couple of reasons.

1st. To take a photo without a flash and without a tripod (I'm talking handheld here), we must 
have a shutter speed one step faster than the Focal length we are shooting at.

Let me explain, Let's say we are shooting a lens that is 100mm-400mm.
If we are at 100mm, we need a shutter speed of at least 1/125sec.
If we are at 200mm, we need a shutter speed of at least 1/250sec.
If we are at 400mm, we need a shutter speed of at least 1/500sec.

NOW, There are exceptions to this rule. (For you Smokey)
Cameras and lenses with image stabalization allow you to shoot shutter speeds below the focal length.
If you have nerves of steel, you can sometimes break this rule.

2nd.  If we are shooting a subject that is moving we need a fast shutter speed.
The faster it is moving, the faster shutter speed we will need.

Bear with me as I take a rabbit trail for a minute and I'll bring
this all together.

We must first understand how f-stops (or Aperture) and shutter speeds work together.

As f-stops go up, shutter speeds go down.

Okay, A little bit about lenses and I will answer the question about where ISO comes in and Why it is important.

Zoom lenses (which most of us are using) have an f-stop rating on them.
Some examples 3.5-5.6,  4.0-5.6, & 2.8 to name a few. So. What this means is, If we are using the same 100-400mm lens with 
the first example, 3.5-5.6, the fastest f-stop at 100mm will be 3.5 and the fastest f-stop available at 400mm would be 5.6 resulting 
in a slower shutter speed at 400mm than at 100mm.

The reason I put the example 2.8 in red was because, #1, they are expensive and #2, with a 2.8 lens, you get 
the 2.8 f-stop at 100mm and all the way out to 400mm which would give you the same shutter speed at 
each end of the focal length.(100-400). A great advantage when speed is needed!!!

Let's tie this all together with a scenerio.

We are shooting the same lens(100-400mm f3.5-5.6). We do not have a flash or tripod at our disposal.
We are shooting outdoors and it's overcast.
Our subject is our dog running around in the front yard.
Although we have the reach of 400mm, we only need to be at 100mm.

How do we approach this shot so that we get the correct shutter speed to do both, 
(Allow ourselves to handhold the shot and stop the motion of the running dog).
Here's what I would do:

I would set the camera to Aperture Priority.
I would dial the Aperture down to 3.5, because we now know that is going to give us the fastest shutter speed at 100mm.
After pressing the shutter button halfway down, we discover that our shutter speed is only 1/100sec. 
This will not allow us to handhold the shot nor will it stop the motion of the running dog NOW WHAT?

ARE YOU READY?? Here is where ISO comes in to save the day.

Assuming we were at ISO 100, all we have to do is bump that up to ISO200 and try again.
If that's not a fast enough shutter speed, then bump it to ISO400 and so on, until we are getting a suitable shutter speed.

Now I know what you are thinking, The dog is pooped out and has gone inside by now 
With practice you can do this in a matter of seconds if you learn where the controls are.

One Last Question, What is the disadvantage of using higher ISOs?

The higher the ISO, the more noise you will see in the photo. (Or that grainy look).

I have provided 5 examples of this effect shot with a Canon 20D.
They are all 100% crops of the same subject at different ISOs.
A couple of things to notice:
 1.  As everything stays constant except the iso, watch as the shutter speeds go up and the noise gets worse.
Especially in the Blues!!! and darker areas.

1. f5  ISO100  1/50sec.
2. f5  ISO200  1/100sec.
3. f5  ISO400  1/160sec.
4. f5  ISO800  1/400sec.
5. f5  ISO1600  1/800sec.


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## tuffdawg (Sep 10, 2008)

Its times like this when I need a printer.  I have learned so much here in the last 24 hours especially.


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## Smokey (Sep 10, 2008)

DRB1313 said:


> I am going to attempt explaining ISO, it's use and the effects it has on our photos.
> 
> What is ISO?  ISO is basically the sensors sensitivity to light.
> The higher the number, the higher the sensitivity. ie: ISO100, 200, 400, 800, 1000, 1600.
> ...



_(For you Smokey)_ How'd I get drug into this

_Zoom lenses (which most of us are using)_ yeah..everybody but me


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## tuffdawg (Sep 10, 2008)

Smokey said:


> _(For you Smokey)_ How'd I get drug into this
> 
> _Zoom lenses (which most of us are using)_ yeah..everybody but me



Dont feel bad smokey, My camera actually isnt all that ...... Since I have been researching better ones,now i want to do more than I originally  wanted to too begin with.  I never thought I would catch the "bug" that seems to follow a good camera.  I have been wanting a "decent" camera for two years now...... I get a great one, and now its not good enough. ........


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## DRB1313 (Sep 10, 2008)

Your lens IS a zoom lens, not as long as you would like, but it still a zoom lens.
That was a subliminal disclaimer to protect myself from
you calling me out for handholding a shot a while back


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## Smokey (Sep 10, 2008)

DRB1313 said:


> Your lens IS a zoom lens, not as long as you would like, but it still a zoom lens.
> That was a subliminal disclaimer to protect myself from
> you calling me out for handholding a shot a while back


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## DRB1313 (Sep 10, 2008)

Hey! You still got that Gator?


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## Smokey (Sep 10, 2008)

DRB1313 said:


> Hey! You still got that Gator?



As of right now I do.
Someone is suppose to come out tomorrow to look at it.


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## DRB1313 (Sep 10, 2008)

Just wondering when we were going shopping


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## Jake Allen (Sep 10, 2008)

Excellent info and analogies, Doctor! Thanks a bunch.

TD, you can quickly adjust the ISO on your D80 by pressing the button to the left of the screen and turning the knob behind the shutter with your thumb.


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## tuffdawg (Sep 10, 2008)

Jake Allen said:


> Excellent info and analogies, Doctor! Thanks a bunch.
> 
> TD, you can quickly adjust the ISO on your D80 by pressing the button to the left of the screen and turning the knob behind the shutter with your thumb.



THANK YOU!! I kept spending minutes at a time today changing it thru the menu.. 

Thank you for letting me know that!


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## jason308 (Sep 10, 2008)

Nice explanation DRB!!!!!  This one needs sticking!!


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## StriperAddict (Sep 10, 2008)

jason308 said:


> Nice explanation DRB!!!!! This one needs sticking!!


 
Yep, us digital greenhorns need all the help we can get! 

Thanks DRB


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## rip18 (Sep 10, 2008)

Great explanation!  Well done!  I'll add it to the sticky pile up there in Photo Techniques of the Trade...


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## DRB1313 (Sep 10, 2008)

Thanks! I just hope someone can find something useful from all that jabber.


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## Smokey (Sep 10, 2008)

DRB1313 said:


> Thanks! I just hope someone can find something useful from all that jabber.



Believe it or not I understand most of the jabber.
While messing around with the camera on a bright sunny day I had the camera set on ISO 1600 which gave it a really, really fast shutter speed, something like 1/4000.  With the conditions mentioned would there ever be a reason for setting such as those?


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## DRB1313 (Sep 10, 2008)

Absolutely Yes! Even on a bright sunny day there may be something moving really fast,Like a Humming bird.
If you were trying to freeze the wings, this would get you there.
One other thing. When using a high ISO in bright conditions, the
noise factor in the photo is somewhat less.
Digital noise seems to be worse when you are using a high ISO to
get a suitable shutter speed in low light.


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## Smokey (Sep 10, 2008)

DRB1313 said:


> Absolutely Yes! Even on a bright sunny day there may be something moving really fast,Like a Humming bird.
> If you were trying to freeze the wings, this would get you there.
> One other thing. When using a high ISO in bright conditions, the
> noise factor in the photo is somewhat less.
> ...



Thanks


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## FERAL ONE (Sep 10, 2008)

i am the other extreme. at 100 mm i need 1/4000 th shutter speed to hold still. i guess when you look like a bowl of jello, you shake like a bowl of jello !!!   

great job on the explanation drb !!!!


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## DRB1313 (Sep 10, 2008)

And now you and E-man know how to bake cakes


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## StriperAddict (Sep 10, 2008)

Ok, dumb question time 

I was just thinking about the ISO stuff and was wondering about the old film days of ASA, remember?  You could never change (up) the ASA value without seriously DARKENING the final result.  How is that not possible with digital?


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## DRB1313 (Sep 10, 2008)

Here's my shot at answering that.
A roll of film was what it was(Not adjustable). If you wanted a faster, more
sensitive film, you had to change the roll.
The digital sensor is electronic and it's sensitivity is changed by turning a dial.

Sounds good to me.


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## Hoss (Sep 10, 2008)

Great info and discussion.  Thanks DRB for the tutorial.  It'll come in handy for lots of folks.


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## wolfess (Sep 12, 2008)

Now if I can just remember all this while I'm shooting.


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## leo (Sep 23, 2008)

Great explanation DRB

Thanks for sharing it with us


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