ISO Settings

Mclovin101

Mclovin101

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Richard
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Hi all

Can some one explain to me how the ISO works. I have a Cannon EOS1000D and the ISO values are 100 upto 1600 i think
 
ISO is the sensitivity to light of the sensor. 100 is the least sensitive* and will require lots of light and/or a longer exposure and/or larger aperture. As the number gets larger, the sensor becomes more sensitive and the amount of light required to give correct exposure gets less.

The down side to higher ISO is that the pictures will tend to be noisier.


* on most cameras.
 
Unfortunately that is wrong and is a myth perpetrated by websites written by people who also do not understand the purpose of the ISO settings on a camera.

Increasing the ISO does NOT make the sensor more sensitive to light - THAT is fixed by the sensor design - a sensor is made up of millions of light sensitive elements which give out a tiny electrical voltage when light hits them - just like the solar panels which are used to supply electricity.

However the elements in a camera sensor are so small that the voltage generated by them is very small indeed and needs amplifying before it can be sent to the memory cards.

Increasing the ISO is similar to turning up your radio with the volume control - it is called increasing the gain.

Unfortunately everything electrical generates noise - think of turning up the volume control on your CD player and hearing the hiss - and THAT is what generates the "noise" on digital images - we call it "noise" because that's exactly what it is even though it comes out as a granular structure on our pictures.

So the more you increase the ISO (the gain of the amplifier) the more you increase this noise - and it shows most on darker parts of the image because the signal from them is much weaker compared to the lighter parts.

So the higher the ISO the greater the noise - depending on sensor design.

And of course it shows up more on crops because you are simply magnifying the image of the noise as well as the real image.

Hope that clarifies the matter a bit.

.
 
petersmart said:
Unfortunately that is wrong and is a myth perpetrated by websites written by people who also do not understand the purpose of the ISO settings on a camera.

Increasing the ISO does NOT make the sensor more sensitive to light - THAT is fixed by the sensor design - a sensor is made up of millions of light sensitive elements which give out a tiny electrical voltage when light hits them - just like the solar panels which are used to supply electricity.

However the elements in a camera sensor are so small that the voltage generated by them is very small indeed and needs amplifying before it can be sent to the memory cards.

Increasing the ISO is similar to turning up your radio with the volume control - it is called increasing the gain.

Unfortunately everything electrical generates noise - think of turning up the volume control on your CD player and hearing the hiss - and THAT is what generates the "noise" on digital images - we call it "noise" because that's exactly what it is even though it comes out as a granular structure on our pictures.

So the more you increase the ISO (the gain of the amplifier) the more you increase this noise - and it shows most on darker parts of the image because the signal from them is much weaker compared to the lighter parts.

So the higher the ISO the greater the noise - depending on sensor design.

And of course it shows up more on crops because you are simply magnifying the image of the noise as well as the real image.

Hope that clarifies the matter a bit.

.
Click to expand...

Nice work :)
 
Please correct me if im wrong but the lower the ISO the less light will be taken into account and the higher the ISO the more light will be taken into account.

So when is best to use ISO 100 ??? and the same for ISO 1600
 
Use the lowest you can at all times. Only raise it when you cant get the shutter speed/aperture combo you want.

In good light, ISO 100 should be fine, but as the light drops, the shutter speeds will fall. So you'll need to raise the ISO to compensate.

If you were shooting a fast moving object, and wanted to freeze it. At ISO 100 during the day, you might get a shutter of 1/500, which would be enough. When the light starts to fall, but you still want to freeze the subject, you wont be able to get a fast enough shutter, so you'd raise your ISO.

ISO 1600 and above are for when the light is really bad, like at a gig or indoors. Only use it if you have to, dont go around shooting at ISO 1600 in great light outside.
 
Mclovin101 said:
Please correct me if im wrong but the lower the ISO the less light will be taken into account and the higher the ISO the more light will be taken into account.

So when is best to use ISO 100 ??? and the same for ISO 1600
Click to expand...

it is the aperture that determines how much light is let into the camera.

You would usually use ISO100 when there is good light and ISO1600 when there is less light.
 
Mclovin101 said:
Please correct me if im wrong but the lower the ISO the less light will be taken into account and the higher the ISO the more light will be taken into account.
Click to expand...

Wrong, read the above post by petersmart carefully
 
petersmart said:
Unfortunately that is wrong and is a myth perpetrated by websites written by people who also do not understand the purpose of the ISO settings on a camera.

Increasing the ISO does NOT make the sensor more sensitive to light - THAT is fixed by the sensor design - a sensor is made up of millions of light sensitive elements which give out a tiny electrical voltage when light hits them - just like the solar panels which are used to supply electricity.

However the elements in a camera sensor are so small that the voltage generated by them is very small indeed and needs amplifying before it can be sent to the memory cards.

Increasing the ISO is similar to turning up your radio with the volume control - it is called increasing the gain.

Unfortunately everything electrical generates noise - think of turning up the volume control on your CD player and hearing the hiss - and THAT is what generates the "noise" on digital images - we call it "noise" because that's exactly what it is even though it comes out as a granular structure on our pictures.

So the more you increase the ISO (the gain of the amplifier) the more you increase this noise - and it shows most on darker parts of the image because the signal from them is much weaker compared to the lighter parts.

So the higher the ISO the greater the noise - depending on sensor design.

And of course it shows up more on crops because you are simply magnifying the image of the noise as well as the real image.

Hope that clarifies the matter a bit.

.
Click to expand...

I agree that you are technically correct and I could have gone into pages and pages of Epsilons and Sigmas had I chose to, but I was giving a simple answer.

Given the nature of the question it seemed appropriate. I described the function in a photographic environment rather than the engineering behind it. :thumbs:
 
Oggy said:
I agree that you are technically correct and I could have gone into pages and pages of Epsilons and Sigmas had I chose to, but I was giving a simple answer.

Given the nature of the question it seemed appropriate. I described the function in a photographic environment rather than the engineering behind it. :thumbs:
Click to expand...

Well I don't think the answer I gave was difficult for anyone to understand and I believe it's far better to give a reasonably simple correct answer than an even simpler incorrect one.

And of course your answer doesn't explain noise whereas mine does.

.
 
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Won't quote the entire post but *** Petersmart for the post and explaination of ISO

John.
 
Are you guys getting your technicals mixed up?:thinking: It seems like some of you are talking from the perspective of film cameras and some of cameras using digital sensors. On a film camera the aperture does indeed control how much light reaches the film plane as much as the shutter controls how long that light lasts. With digital it gets a lot more complicated and I would point to the aptly named Petersmart for that one. Hats off to you for a knowledge way way beyond mine.:)
 
So, the noise on the pictures at higher ISO is caused by the electrical current being increased on the sensor elements? Or have I got the wrong end of the stick?
 
steelerdean said:
So, the noise on the pictures at higher ISO is caused by the electrical current being increased on the sensor elements? Or have I got the wrong end of the stick?
Click to expand...

Slightly - the electrical current isn't usually increased on the sensor elements since that would increase thermal noise (In fact if you're using live view there is a warning about using it for too long).

I tried to give a simplified explanation of noise because I thought that would be easiest, but here is a slightly more thorough explanation:

Digital sensors work by absorbing photons (light) and generating electrons (electrical energy).

Unfortunately when they do this they also generate a small amount of noise (called photon noise) and, also unfortunately for us, photon noise is generated as the square root of the photons.

What this means for us is that the lower the light reaching the sensor the more noise is generated relative to the signal, so noise is greater in dark areas.

Thermal noise is another factor - which simply put means that the noise levels from almost any electrical device will increase with increasing temperature.

When a digital sensor is hit by light it generates a very small signal but this is an ANALOGUE signal which means that it has to be converted to digital format before it can be stored on the camera's memory card.

All digital formats work in the binary system in which a series of 1s and 0s is represented by an electrical charge on memory cards, CPUs, computer memories etc.

The voltage levels required to implement the 1s and 0s depend on the device but will alway be several orders of magnitude above the levels of the photodiodes in the sensor.

So before this signal can be digitised it has to be amplified and as already explained the signal is so low (even in bright light) that we get noise contributed not only by the physics of the sensor but also by the amplification process.

Once the signal is amplified it then goes through the camera's A/D converter which takes the analogue signal and converts it into the digital signal required by the memory cards.

And this process also contributes a small amount of noise called digitisation noise.

This is a fuller explanation but does not take everything into account - for those who want to go further two further sources of reading:

http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/

http://www.clarkvision.com/articles/digital.sensor.performance.summary/

The physics of digital sensors and noise is extremely complex - the miracle really is that they actually work at all giving the obstacles which have to be overcome to give us the images we so casually take for granted.

.
 
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hornetsixer said:
On a film camera the aperture does indeed control how much light reaches the film plane as much as the shutter controls how long that light lasts. With digital it gets a lot more complicated ...
Click to expand...

The physics of digital cameras is totally different from the physics and chemistry of films but on both types of camera the aperture and the shutter both work identically - it's what happens afterwards that is different.

.
 
Sod all the technical jargon, on your camera use 100 if you can and only go higher if you need a faster shutter speed such as in low light. 800 is about the max before noise starts to noticeably kick in and 1600 is ok for a record type shot, but never going to be the best

Might even find you can expand it to 3200, but that ain't going to be great, but better than nothing
 
tijuana taxi said:
Sod all the technical jargon, on your camera use 100 if you can and only go higher if you need a faster shutter speed such as in low light. 800 is about the max before noise starts to noticeably kick in and 1600 is ok for a record type shot, but never going to be the best

Might even find you can expand it to 3200, but that ain't going to be great, but better than nothing
Click to expand...

Pretty sensible advice IMO. I think there's an element of "it depends" as well.

It depends on your camera. For example ISO 100 on my superzoom (Canon SX10is) is quite similar to ISO 800 on my Micro Four Thirds Panasonic G3. I have hardly ever used ISO 800 successfully on my SX10.

It depends on the type of image. Noise tends to show up more in areas of plain colour and shadows. You can get away with higher ISOs for some images than others.

It depends on the viewer's tolerance for noise. Some people can't stand having any noise at all visible in their images, other people aren't bothered by a bit of noise. In fact, some people think a little noise can sometimes enhance an image.

It depends on the type of noise. Noise can involve random spots/blotchiness of either colour ("chroma") or brightness ("luminance"). Don't know if it is generally true, but for me at least I have more tolerance for a bit of luminance noise than for chroma noise.

It depends on how large you are going to view or print an image. The larger the image, the less noise it should have in order to be acceptable.

It depends on how much you crop an image. The more you crop, the more prominent the noise will become.

It depends on whether you post process or not. If you post process then you can reduce the noise, but in doing this you will also lose details. Whether you can get an image to an acceptable degree of noise without sacrificing too much detail depends on all the previous things, and also on how good your post processing technique, how good your processing software is with noise, and how much time you have available to process the image.

It depends on your camera settings. You may be able to turn noise reduction up or down in your camera. The same considerations about losing detail apply as with post processing.

It may depend on whether you use RAW or not. I don't know, I don't use RAW, but I imagine you would have a bit more flexibility in dealing with noise if you use RAW.

Another consideration is colour. Higher ISOs tend to produce desaturated images. Here too post processing can help to some extent.

Some people simply won't use ISOs above a certain amount, which is fair enough. But I'm with Rich, in the "it can be better than nothing" brigade.

For example, these images would not be good enough quality for some people, but they are fine for my purposes. I think you should experiment to find out what works for you.

ISO 3200

0383 41 2011_09_04 P1130459 ISO3200 PS2 NoLu33,2,2BuHiExCuNoLu33,2,2 900hSS72x0.3 by gardenersassistant, on Flickr


ISO 3200

0383 48 2011_09_04 P1130564 ISO3200 PS1 NoLu33,2,2CrClExLebNoLu33,2,2 900hSS32x0.3 by gardenersassistant, on Flickr


ISO 6400

0383 49 2011_09_04 P1130595 ISO6400 PS1 NoLuCo100+8,37+2,5,5ExLeb900hSS45x0.3 by gardenersassistant, on Flickr
 
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