ISO and the meaning thereof

[delko]

Hey

ISO.

Can someone clear up some frustration.

Ok so i know ISO is like the film speed.

The rate of the light that enters the camera...

So a low ISo like 100 will give a very smooth photo with less noise as a 1600 iso will have much more noise.

Do you ussualy select your ISo manual or automaticly?

I know it is part of the exposure triangle....

Can anyone give me some tips on ISo.

Any unexpected effects and art effect that can be used when thinking about ISO.

Thank you

 

[enzodm]

Manually, the lowest possible.
You may use auto if in need of taking a picture with mandatory shutter and aperture, but usually you want it as low as possible, eventually taking into account the rule of exposing to the right .

 

[molested_cow]

ISO for film photography is very different from ISO for digital.

There are many threads on this, you can search for them for better explanation, but I will take a shot here.

ISO for film:
ISO refers to the speed of the film. Film have photo cells on them that react to light, therefore forms the image. Low ISO rating means the photo cells are smaller and react slower to light. Where as high ISO rating have bigger cells that react quicker to light. That's why low ISO films look smoother but requires more exposure to light.

ISO for digital:
ISO for digital refers to the noise. There is no "photo cell" on digital sensors, just pixels. Each pixel has a certain sensibility to light. When a pixel takes in light, it needs to know how much to take in. Too little, you don't get enough information. Too much, you get too much information. The main things, you want the "right information", and any unwanted information is therefore the "noise". So when setting your camera to low ISO rating, it's telling the sensor to filter more light, giving you what you need. However, when trying to take photo in low light, you increase the ISO rating, telling your camera to grab more light. When that happens, you camera will also grab those unwanted information, presented as noise.

That's why older digital sensors are less capable and therefore perform less well in the same ISO rating as newer and improved sensors at the same setting.

ISO for digital is therefore a nostalgic way of explaining noise, using film speed as a reference.


In taking photo, the concept of ISO applies the same. For me, I think about either aperture or shutter speed first. Then I see what ISO setting will allow me to take the photo at my preferred aperture or shutter speed. The lower the better of course.

 

[BlairWright]

Set ISO manually.

The easy way to determine ISO is to set your apeture and adjust your ISO to meet your shutter speed requirements. You can do the opposite too.

Example: if you have a 200mm lens (optimally you want your shutter speed a min of your lens length) at f/4 and you meter for 1/160 and your ISO is at 100 you need one stop of ISO to set your shutter speed to 1/200, adjust ISO up a stop the shutter speed.

 

[Helen B]

The meaning of ISO speed is widely misunderstood, mainly because almost all of the people who write about it have never read the relevant ISO* Standards, or even read something by someone who has actually read them.

In a nutshell the ISO speed of negative still film is based on the very minimum amount of light required to have the minimum effective rise up from totally unexposed film, while being developed to a fixed contrast value. The ISO speeds of a digital still camera are based on the maximum amount of light that would cause the brightest likely highlights to be washed out ('saturated' in technical-speak) while setting. Camera manufacturers are, however, permitted a lot of discretion, much more than film manufacturers, and noise criteria can also be used while keeping the same general guides. The standard for digital cameras was set so that the digital ISO speed would be roughly similar in look to film of the same speed - although this can only ever be a rough similarity. As others have said, the payoff of increased speed is usually increased graininess or noise, and some decrease in latitude or dynamic range. Improved technology is decreasing these downsides for both film and, more dramatically, digital.

*International Organisation for Standardisation in English - whose short international name was chosen to be ISO, pronounced as an acronym.

Best,
Helen

 

[DiskoJoe]

if you know what iso you want to use then dial it in manually. If you dont then use the auto feature.

 

[SCraig]

ISO for film photography is very different from ISO for digital.

There are many threads on this, you can search for them for better explanation, but I will take a shot here.

ISO for film:
ISO refers to the speed of the film. Film have photo cells on them that react to light, therefore forms the image. Low ISO rating means the photo cells are smaller and react slower to light. Where as high ISO rating have bigger cells that react quicker to light. That's why low ISO films look smoother but requires more exposure to light.

ISO for digital:
ISO for digital refers to the noise. There is no "photo cell" on digital sensors, just pixels. Each pixel has a certain sensibility to light. When a pixel takes in light, it needs to know how much to take in. Too little, you don't get enough information. Too much, you get too much information. The main things, you want the "right information", and any unwanted information is therefore the "noise". So when setting your camera to low ISO rating, it's telling the sensor to filter more light, giving you what you need. However, when trying to take photo in low light, you increase the ISO rating, telling your camera to grab more light. When that happens, you camera will also grab those unwanted information, presented as noise.

That's why older digital sensors are less capable and therefore perform less well in the same ISO rating as newer and improved sensors at the same setting.

ISO for digital is therefore a nostalgic way of explaining noise, using film speed as a reference.


In taking photo, the concept of ISO applies the same. For me, I think about either aperture or shutter speed first. Then I see what ISO setting will allow me to take the photo at my preferred aperture or shutter speed. The lower the better of course.

I must admit that I've never seen ISO explained quite that way before.

 

[enzodm]

....

I must admit that I've never seen ISO explained quite that way before.

most likely because it is not really true.
Light hitting sensor is always the same: the voltage measured at each pixel is amplified more with high ISO before digital conversion, that's all. Nothing filters light, except... filters (and aperture diaphragm).
And by the way, if there exists something like a photo cell, that is exactly the pixel. Film has silver salt grains of variable size, from which depend sensitivity to photons - the larger, the more sensitive, the less photons needed, nothing related to "speed of reaction".

 

[molested_cow]

Good to know that I'm wrong!

 

[KmH]

ISO for film:
ISO refers to the speed of the film. Film have photo cells on them that react to light, therefore forms the image. Low ISO rating means the photo cells are smaller and react slower to light. Where as high ISO rating have bigger cells that react quicker to light. That's why low ISO films look smoother but requires more exposure to light.There are no photo cells on film.
Film has a light sensitive chemical (like silver halide crystals) in on it that are imbedded in a gelatin emulsion.
The size of the light sensitive chemical grains (think sand) determines how sensitive to light the film is.
Small grains of the chemical are used to make low ISO film and being very small, the grains are very difficult to see. Large grains make high ISO film and being bigger make high ISO film look "grainy". The light sensitive grains can also quit reacting to the light in a time frame that varies with film emulsion chemistry, which is known as reciprocity failure.

ISO for digital:
ISO for digital refers to the noise. There is no "photo cell" on digital sensors, just pixels. Each pixel has a certain sensibility to light.
A pixel is indeed a "photo cell".
Each pixel is an analog electronic device known as a photoreceptor. In fact, the image sensor in all digital cameras is an analog device, not a digital device.
Each photoreceptor (pixel) developes an analog voltage proportional to how much light falls on the photoreceptor. More light falling on the pixel developes a larger voltage.Because pixels are very small and individually record much light, the voltage they develope has to be amplified by analog amplifer circuits that are also on the image sensor chip. Those amplifier circuits are what are adjusted to change the camera's ISO setting.
The amplified analog voltage of each pixel are then sent through another electronic device, known as an analog-to-digital converter (A/D converter), that changes the analog voltage to a binary digital number. It is at that point that the image data becomes 'digital".

I added some clarifications.

 

[Derrel]

ISO = In Search Of... For example: "Single divorced dad seeks accomplished professional woman for movie dates, dining out." You know, "in search of".

But in the context of photography, ISO can simply be reduced to "sensitivity to light". Forget about the technical terms. ALso, FORGET about the advice to "keep the ISO as low as possible". That is bad,bad,bad advice for people who barely know what ISO means or does. Set the ISO to a level that ensures the BEST opportunity to get good photos with the equipment you have to use with you. For most beginners, with a kit lens and a pop-up flash, the camera's lowest ISO setting is nothing except a hindrance...a shot-ruiner, for most of the year. This time of year, with weak late autum sunlight levels, shooting with a kit lens at ISO 100 is flat-out stoooopid. For shooting holiday bounce-flash shots, with Christmas trees in the background, the low sensitivity of ISO 100 ensures that the Christmas lights will look dim and pale and tiny.

I often suggest that for bounce flash shooting, the very first thing to do is to elevate the ISO to 500,640,or 800. Seriously. On a full-frame camera, ISO 640 + bounce flash looks quite good. The idea that an ISO of 100 will give a very "smooth photo" is correct--and if there is ANYTHING Moving in the image, it will often be a nice, smooth, fuzzy, smeared image. ISO 400 is your friend, beginning shooters. Visit him sometime. Have a nice, day-long chat. Spend a weekend with ISO 400. See what an awesome friend he is.

 

[mc1979]

Derrel, I had seen this advice from you in a previous thread about keeping ISO 400 for beginners. I kept this in mind while shooting a newborn not long ago.. of course all for practice. I used only natural light from a window and on all shots where I had the baby on a cream colored blanket, they turned out great. On shots where I had him on a darker blanket, I could see a lot of grain after loading them. I used noise reduction in LR during processing and this seemed to help but I have this question. I think I read somewhere there in a "print" you don't notice grain like you do on a screen. Is this true?

 

[Robin Usagani]

If you shoot Nikon, I would suggest learning how to use Auto ISO.

If you shoot Canon, forget about it.. it sucks. Unless you have the 1D series I think where you can set lower and higher limit of the shutter with auto iso and aperture priority.

 

[Derrel]

Derrel, I had seen this advice from you in a previous thread about keeping ISO 400 for beginners. I kept this in mind while shooting a newborn not long ago.. of course all for practice. I used only natural light from a window and on all shots where I had the baby on a cream colored blanket, they turned out great. On shots where I had him on a darker blanket, I could see a lot of grain after loading them. I used noise reduction in LR during processing and this seemed to help but I have this question. I think I read somewhere there in a "print" you don't notice grain like you do on a screen. Is this true?

QUite often, prints do not show noise all that much...it tends to be sublimated quite a bit in prints. If one looks at DxO Mark's sensor performance ratings, they have a print-normalized comparison score, graphed out. They talk about it here, briefly DxOMark - Viewing conditions

I still maintain that MANY people are way,way,way overly concerned about slight amounts of digital noise.I have seen on-line images posted where users complain about noise, and I look at the image and thing, "huh...looks pretty good,actually." My experience is that noise is more-noticeable on-screen than in normal-sized prints of 5x7 to 8x10 inches. Also, blurred, smear images with no discernable noise really suck, compared to slightly noisy, SHARP images, with adequate shutter speeds and decent depth of field, and well-exposed bounce flash shots always look better than ones that are 1 to 3 stops underexposed because at ISO, the flash did not have enough "oomph!" to light up the scene.

Natural-light/window-light photography is a great example of where ISO 400 can put your pictures right in to the "zone" of good,safe,workable shutter speeds and overall exposures, and where ISO 100 is just begging for problems. The advice to keep the ISO level at lowest possible is no longer good advice for the majority of newer D-SLRs...it's like driving at 35 MPH because it is "safer" than 55 MPH. Yeah, it is "safer"...until you get rear-ended for going too slow, and your car's messed up...

 

[Rephargotohp]

ALso, FORGET about the advice to "keep the ISO as low as possible". That is bad,bad,bad advice for people who barely know what ISO means or does.

It's only bad advice because it is being misinterpreted.
"Lowest possible" does not refer to the Camera's Lowest possible but rather the Conditions.

In other words if you believe you require the settings of f/8 @ 1/200 The "lowest possibl""e outdoors on a nice sunny day and the" lowest possible" indoors, would be quite different. That's what that refers to

I think if someone is learning and they are learing Aperture and Shutter speed, they should know that also (why they have to change ISO)