ISO Speed Question

[SDPPM]

Are we only increasing the iso speed to handle low light ? Do we want to use the lowest possible ISO Speed all the time or are there other reasons to go higher. What is the trade off when we do go to a higher ISO speed.

 

[SNGX1327]

well, there are plenty of reasons to increase ISO speed.

regardless of what lighting you are in, if you have a given exposure value, let's say 1/250s and f/5.6 at ISO100. well increasing your ISO one stop to ISO200 will give you an extra stop to apply to either your shutter speed or your aperture. you can hop up to 1/750s and stop a lot of motion (say, sports?) or you could stop the aperture down to f/8.0 to get an increase in your depth of field. OR you could meet each halfway and switch to 1/500s, f/6.3, and ISO200.

 

[joe mama]

Are we only increasing the iso speed to handle low light ? Do we
want to use the lowest possible ISO Speed all the time or are there
other reasons to go higher. What is the trade off when we do go to a
higher ISO speed.

The only reason to up the ISO to get a faster shutter speed. The consequences of upping the ISO is more noise and less detail. So, you want to use the lowest ISO possible that will still give a "sufficiently fast" shutter speed. Sometimes, it's a matter of balancing what constitutes "sufficiently fast" vs the image degradation of using a higher ISO.

For example, let's say you're taking sports pics. The higher the shutter speed the better, since you want to freeze the action. However, you may decide that, say, 1/500 is "fast enough", even though 1/1000 would be better, since you'd rather get a cleaner image using ISO 400 than ISO 800.

Usually, people tend to sacrifice DOF to get a faster shutter, rather than up the ISO. For example, they'll shoot a pic a f/1.4 ISO 400 rather than f/2.8 ISO 1600. In my opinion, noise is less an issue than motion blur, camera shake, and/or "improper" DOF (and all that comes with it -- softer corners and increased vignetting, for instance). But most people seem to think that noise is "Enemy #1" and will do anything , from using a shutter speed that is too low to using a DOF that is too shallow, to avoid it.

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

 

[SNGX1327]

Are we only increasing the iso speed to handle low light ? Do we
want to use the lowest possible ISO Speed all the time or are there
other reasons to go higher. What is the trade off when we do go to a
higher ISO speed.

The only reason to up the ISO to get a faster shutter speed. The
consequences of upping the ISO is more noise and less detail. So,
you want to use the lowest ISO possible that will still give a
"sufficiently fast" shutter speed. Sometimes, it's a matter of
balancing what constitutes "sufficiently fast" vs the image
degradation of using a higher ISO.

that makes absolutely no sense.

let's say i'm shooting baseball from the bleachers with a 200mm lens. by my "rule", i need at least 1/500s to hand hold that lens. if i have 1/500s @ f/4 and ISO400, but decide that i want more DOF, i can easily go to 1/500s @ f/8 and ISO1600.

DOF isn't always the reason. that example is with a 70-200 f/4L, it's sharp wide open. if you have a cheapo 70-300mm lens you will get your sharpest images when you stop down. taking a photo at f/8 is a lot of times much sharper than at f/5.6 (wide open). so i used to often turn my ISO up, hold shutter speed the same, and stop down the aperture to get a sharper image.

so DOF and sharpness are two reasons to change ISO. no "only" shutter speed.

Usually, people tend to sacrifice DOF to get a faster shutter, rather
than up the ISO. For example, they'll shoot a pic a f/1.4 ISO 400
rather than f/2.8 ISO 1600.

that also doesn't make sense. i'm not saying people don't do it, but it doesn't make sense to me. shutter speeds being the same, i guarantee you the pic at f/2.8 and ISO 1600 looks better than the pic at f/1.4 and ISO 400 because of DOF and sharpness (stopping down) reasons.

but the main point is that there are three variables in your exposure value. Tv+Av+ISO = EV. if you increase one amount of light hitting the sensor because of one, another has to lower. OR two others have to lower to add up to the sum of the change. in other words, shutter speed isn't the ONLY thing to raise ISO for...

 

[joe mama]

The only reason to up the ISO to get a faster shutter speed. The
consequences of upping the ISO is more noise and less detail. So,
you want to use the lowest ISO possible that will still give a
"sufficiently fast" shutter speed. Sometimes, it's a matter of
balancing what constitutes "sufficiently fast" vs the image
degradation of using a higher ISO.

that makes absolutely no sense.

I'm listening.

let's say i'm shooting baseball from the bleachers with a 200mm lens.
by my "rule", i need at least 1/500s to hand hold that lens. if i
have 1/500s @ f/4 and ISO400, but decide that i want more DOF, i can
easily go to 1/500s @ f/8 and ISO1600.

Did I say otherwise? What I said is that most seem to prefer to shoot f/4 1/500 ISO 400 than f/8 1/500 ISO 1600 even if f/8 were "preferable" in terms of DOF. I most certainly did not say that the latter was not a possiblity, or even the "better" way to go about it.

DOF isn't always the reason.

Never said it was. Please reread what I wrote. I said people would rather "sacrifice" DOF than increase the ISO.

so DOF and sharpness are two reasons to change ISO. no "only" shutter
speed.

You misinterpret. You change DOF and sharpness with f-ratio, not ISO. ISO only changes the shutter speed. Now, when you increase f-ratio to get more DOF and/or sharpness, you often need to up ISO to keep the shutter speed "sufficiently high". Thus, as I said, you increase ISO only to increase shutter speed.

Usually, people tend to sacrifice DOF to get a faster shutter, rather
than up the ISO. For example, they'll shoot a pic a f/1.4 ISO 400
rather than f/2.8 ISO 1600.

that also doesn't make sense. i'm not saying people don't do it, but
it doesn't make sense to me. shutter speeds being the same, i
guarantee you the pic at f/2.8 and ISO 1600 looks better than the pic
at f/1.4 and ISO 400 because of DOF and sharpness (stopping down)
reasons.

Seriously -- reread my post. I never said otherwise.

in other words, shutter speed isn't the ONLY thing to raise ISO for...

Yes, it is. If you increase ISO, the only effect it has is increasing shutter speed and noise. That's it. Now, you may be forced to increase ISO because you choose to increase f-ratio for more DOF and/or sharpness, and I said exactly that.

For example, let's say you're at 1/100 f/1.4 ISO 400. But f/1.4 is too shallow/soft and you want the DOF/sharpness of f/2.8. So you increase the f-ratio to f/2.8. Now your shutter speed is 1/25 -- too slow. So, you up the ISO to 1600. Why? To increase the shutter speed back to 1/100.

But most people will try to instead shoot 1/100 f/1.4 ISO 400 'cause they don't want to go to ISO 400. Others will instead try 1/50 f/2 ISO 400 and take a chance on the slower shutter speed. No one wants to up the ISO, and they do it only to increase shutter speed.

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

 

[ARShutterbug]

I want to use the lowest possible film speed to avoid the noise problems, but I also avoid high ISO speeds because of the increased file sizes. ISO 3200 sucks my storage space, and it does not accept much pushing during development.

--
http://www.pbase.com/arshutterbug/

 

[NWcityguy2]

I agree, what you said makes no sense. I also reread you post and I don't think either of us misinterpreted it. There are four reasons to increase the Iso. The first three have been covered...

To increase aperture and maintain shutter speed.

To increase shutter speed and maintain aperture.

To increase both shutter speed and aperture to equal the iso increase.

AND

To increase exposure. Either by a full stop or in increments.

I do the fourth all the time as well. Most of the time this is to increase exposure accuracy when I feel it will be off, but occasionally I do is purposely to over expose. And yes, I have used Iso for this purpose.

I really don't know why you are trying to make this point. Maybe in your mind, the only reason to increase Iso is to get a faster shutter speed. And if you were to say that you never raise the Iso but to do just that than I doubt many people will disagree. But to say that it is the only reason everyone raises Iso...

--



Yawn...

 

[Ray Chen]

The only reason to up the ISO to get a faster shutter speed.

That's a false generalization, as not all light are continuous.

--
_ _
\ / ~
~ \ ~ ~ ~ o

 

[Tom Bennett]

I use the canon 5d and rarely shoot below 400iso unless i need a shallow dof

and do not worry even at 3200iso if the print is not going to be larger than 8x10

 

[joe mama]

I agree, what you said makes no sense. I also reread you post and I
don't think either of us misinterpreted it. There are four reasons
to increase the Iso. The first three have been covered...

To increase aperture and maintain shutter speed.

To increase shutter speed and maintain aperture.

To increase both shutter speed and aperture to equal the iso increase.

Wait -- the above three things are what I said, and you said it "makes no sense"?

AND

To increase exposure. Either by a full stop or in increments.

Yes, I did omit that.

I do the fourth all the time as well. Most of the time this is to
increase exposure accuracy when I feel it will be off, but
occasionally I do is purposely to over expose. And yes, I have used
Iso for this purpose.

I'll concede I ommitted that use. This is the first I have heard of someone purposely using a higher ISO to force overexposure.

I really don't know why you are trying to make this point. Maybe in
your mind, the only reason to increase Iso is to get a faster shutter
speed. And if you were to say that you never raise the Iso but to do
just that than I doubt many people will disagree. But to say that it
is the only reason everyone raises Iso...

Well, like I said, you gave four reasons to increase ISO, and the first three I had mentioned, and all were to increase shutter speed. The last, I concede, is a reason I had never heard of before.

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

 

[joe mama]

The only reason to up the ISO to get a faster shutter speed.

That's a false generalization, as not all light are continuous.

I have no idea what that means.

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

 

[subroc]

I am pretty much a novice here and am reasonably sure the experts will state their positions as well.

You select, as an exposure parameter, either shutter speed or aperture. ISO is, for the most part, only increased to gather additional light to allow chosen parameters on aperture and shutter speed. You don’t build an exposure around ISO, you gather more light or light sensitivity to allow you to use “chosen” aperture or shutter values.

You decide you need a specific shutter speed, it may be a minimum, whatever, and you select it. You determine the needed or acceptable aperture or aperture range and you select it. The final adjustment available is ISO or light sensitivity. In essence, if you have reached your desired exposure parameters without adjusting ISO, there is no need to make that adjustment. The reverse can also be made. Select aperture, then needed shutter speed, verify exposure, adjust light or light sensitivity with an ISO adjustment to achieve desired exposure.

That is my understanding of the whole thing.

If the experts want to critique this, feel free, but give an example of when ISO would be the first decision in the exposure chain.

In answer to you question, “what is the trade off,” the trade off is noise.

 

[thien nguyen]

I have a agree with Joe on this. At least, it's what I am doing
unless someone can convince me otherwise.

Before I even look at the viewfinder, I usually have decided
on the aperture and have already set it.

Changing the ISO usually come with corresponding change
to speed.

I would only go back to changing the aperture when
reaching the highest acceptable ISO and still can't get
the speed I wanted.

--
Thien

 

[ARShutterbug]

http://en.wikipedia.org/wiki/Continuous_spectrum

--
http://www.pbase.com/arshutterbug/

 

[Gianni Nuzzi]

in other words, shutter speed isn't the ONLY thing to raise ISO for...

Yes, it is. If you increase ISO, the only effect it has is
increasing shutter speed and noise. That's it. Now, you may be
forced to increase ISO because you choose to increase f-ratio for
more DOF and/or sharpness, and I said exactly that.

Joe,

This is true, but only if you shoot in Av mode.

If you increase ISO in Tv mode, the only effect it has is increasing DOF and noise.

If you increase ISO in M mode, the only effect it has is increasing the overall exposure and noise.

--
Gianni

http://www.pbase.com/gianuz

 

[NWcityguy2]

Well, like I said, you gave four reasons to increase ISO, and the
first three I had mentioned, and all were to increase shutter speed.
The last, I concede, is a reason I had never heard of before.

I don't think it is that uncommon, but I do only use it in specific circumstances. Usually when I have a fairly exact shutter speed and aperture combo which I want to use. Take action and sports for example, with my 70-200mm 4 I like to use 1/800 and between 4 and 5 aperture. If I feel my pictures are going to be under exposed even though my light meter says they are fine I will bump the iso up and then tell my camera to just over expose a stop. The most common time I do this is on is overcast days, where my camera has under exposed consistantly by a stop or more.

--



Yawn...

 

[NWcityguy2]

I think a lot of people think of it in those terms because a very popular camera mode here is Av, and countless discussions have focused on DOF and it's effects. So if you have already mentally pictured how you want your picture to turn out, and thinking in terms of aperture than sure, Iso will only affect shutter speed up to your camera's maximum.

But for someone like me who often shoots in Tv, and thinks in terms of shutter speeds it is the exact opposite. Need a smaller aperture? The easiest way to do that is to raise the Iso in my mind. And I'm not just talking about high shutter speeds also. I will use Tv mode for maximum DOF as well. If I am in a hurry and don't have time to spend on every single shot I will just set the shutter to the minimum I can safely hand hold it. That way my DOF is always the most I can get without camera shake. If I feel that it is not enough, I'll raise the Iso to get more.

I have a agree with Joe on this. At least, it's what I am doing
unless someone can convince me otherwise.

Before I even look at the viewfinder, I usually have decided
on the aperture and have already set it.

Changing the ISO usually come with corresponding change
to speed.

I would only go back to changing the aperture when
reaching the highest acceptable ISO and still can't get
the speed I wanted.

Once again, you are taking three equal things and prioritizing them. Aperture being the most important, than Iso, than shutter speed coming into play only if it will ruin the picture. But just because that is how you order things doesn't mean that everyone thinks in those same terms.

--



Yawn...

 

[SNGX1327]

The only reason to up the ISO to get a faster shutter speed. ...

that makes absolutely no sense.

I'm listening.

let's say i'm shooting baseball from the bleachers with a 200mm lens.
by my "rule", i need at least 1/500s to hand hold that lens. if i
have 1/500s @ f/4 and ISO400, but decide that i want more DOF, i can
easily go to 1/500s @ f/8 and ISO1600.

Did I say otherwise? What I said is that most seem to prefer to
shoot f/4 1/500 ISO 400 than f/8 1/500 ISO 1600 even if f/8 were
"preferable" in terms of DOF. I most certainly did not say that the
latter was not a possiblity, or even the "better" way to go about it.

you said!

"The only reason to up the ISO to get a faster shutter speed."

i don't see how, say, shooting in Tv mode at 1/500s, f/5.6, ISO 400, and increasing my ISO from 400 to 800 to get 1/500s, f/8.0 is "increasing shutter speed".

 

[Jeremy]

I don't think it is that uncommon, but I do only use it in specific
circumstances. Usually when I have a fairly exact shutter speed and
aperture combo which I want to use. Take action and sports for
example, with my 70-200mm 4 I like to use 1/800 and between 4 and 5
aperture. If I feel my pictures are going to be under exposed even
though my light meter says they are fine I will bump the iso up and
then tell my camera to just over expose a stop. The most common time
I do this is on is overcast days, where my camera has under exposed
consistantly by a stop or more.

This is why I wish Canon would implement proper auto ISO in Av, Tv, and M modes. I want to be able to set aperture and/or shutter, and have the camera automatically set ISO for proper exposure. Of course, there will be times when I want ISO 200 or 800 and a given aperture, and the camera will select the proper shutter speed. If it works one way, why can't it work the other way?

--
Jeremy

 

[NWcityguy2]

This is why I wish Canon would implement proper auto ISO in Av, Tv,
and M modes. I want to be able to set aperture and/or shutter, and
have the camera automatically set ISO for proper exposure. Of
course, there will be times when I want ISO 200 or 800 and a given
aperture, and the camera will select the proper shutter speed. If it
works one way, why can't it work the other way?

While an Auto Iso mode like Nikon has would be great, the problem here is the light meter. The camera will think it is exposing a scene correctly, while in reality it is a full stop or move under exposed.

--



Yawn...