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how to explain ISO to newbies Anonymous
how do you explain ISO in layman's to beginners in photograhy

i want to explain it so that it still kind of makes sense and is true, if they ever decide to call me out on it

i was thinking, let's say a camera has a base ISO of 100 and a maximum of 1600

if the camera at base ISO takes 1 second to take a picture, it takes it at the best quality possible because every single pixel on the sensor needs to be exposed to light to make your image

now, at ISO 1600, you get faster shutter speeds, therefore the sensor is exposed to less light than it would have at base ISO. so the camera just makes up the info and extrapolates it from neighboring pixels. so that's why we get noise in images at higher ISO, it's just random pixels of colors approximated to make the image

is that good or what, help me make it better
>> Jeremo !iKGMr61IHM
so i was reading the wiki to try and help... fuck it nearly blew my head off.

There is so much technical shit to know about photography... man... ive barely scratched teh surface

http://en.wikipedia.org/wiki/Film_speed
>> tizzou !!HuouSd+PYUs
>How do you explain ISO to a beginner?

Well, ISO is how sensitive the sensor or film is to light. The lower the ISO (100, 200), the more light needed for a proper exposure. The higher ISO (1600, 3200), the less light needed for a proper exposure.

ISO is also has a direct connection between shutter speed and the aperture. Let's say to expose a picture properly you need 1/250 atr f8 with ISO 400, well, if you want a faster shutter speed, you can half the exposure to 1/500, but to make up for the loss of light you would double the ISO to 800.
>> Anonymous
sorry dudes, i forgot to say, ISO and noise

assuming people already know about balancing aperture, shutter speed and ISO

i want to explain why shit gets noisy at high ISO
>> tizzou !!HuouSd+PYUs
>>265553
>noise

i dunno, lol

Your explanation in OP seemed like it made sense to me.
>> Butterfly !xlgRMYva6s
Someone posted a description of a sensor as a collection of buckets during a thread about base sensitivity.

Made quite a lot of sense but I cant remember all of it to explain it using that terminology so does anyone have it?
>> tizzou !!HuouSd+PYUs
IIRC, big buckets were required for ISO 100/200 so when you got up to 3200, the buckets weren't get filled with as much light and there was just random spaces in between, where as if you started with buckets made for 1600 then there wouldn't be much noise.
>> Anonymous
>>265581
>>265585

I posted that giant shitlong post (2 actually) about sensor physics and noise vs. sensor size. This is a comparatively easy topic.

When you're talking about film, ISO (or ASA) refers to the sensitivity of the film. As you probably know, film is made of up grains of silver halides which turn black after a certain number of photons have hit them. A faster film (ASA 400, say instead of ASA 50) will have larger grains. Because the grains are larger, they can absorb aalllll the photons in a larger area. So they don't need as much light coming in the lens to make a proper exposure. Obviously larger grains means less detail in the image. Using smaller grains means each one sees fewer photons and therefore needs a longer exposure, but the detail is better.
This topic is actually significantly more complicated than that - the image is latent before developing, comparing dynamic range to chemical sensitivity, flip-point distributions, quantum noise, and so on - but that's waaay too detailed for here).

So that explains why fast films are grainy and slow films are smooth. But how does that apply to a digital sensor?

In your camera's CMOS or CCD sensor, each pixel is represented by a little photon gathering well. These wells can store up to a certain number of photons before overflowing (blowing out to white), and it's the job of the shutter and aperture to keep the number under the sensor's maximum. Ideally, something that is white in your image will fill up the sensor's wells completely, and something black will have no photons in it. This is using your sensor to its maximum efficiency.

Now, because you can't increase the sensitivity of these wells to photons (a "full" well will always require the same number of them, unlike film), you should theoretically always need the same amount of light, right? If there's more, then you can close down the aperture, but if there's less, you're screwed?
>> Anonymous
No, because something that you can do with a digital sensor, though, that you can't with film, is turn up the GAIN. This is like turning up the volume control on a stereo. It literally amplifies the signal coming out of each pixel, multiplying whatever was in the photon well. If a white object in your scene is only filling the well half-way, then just multiply everything by 2 and your white object will still look white. Your blacks will still be black (0x2 = 0) and everything else in the middle will slot in where it belongs. This action is equivalent to changing from ISO 100 to 200 to 400 to 800 and so on. Every time you go up a stop in ISO, you double the gain on the signal coming from the sensor.

So where does noise come from then?

Simple. Sensors are sensitive to more than just visible light. Infrared and ultraviolet light can create images on the CCD. Thermal energy (heat) can cause some photon wells to register higher values than they should. So can leakage of electrical charge from adjacent wells. Even quantum noise, wells basically just adding photons for no apparent reason, occurs regularly. These are the fundamental causes of noise in an image. They're always in the sensor to the same level, regardless of what ISO you have the camera set to. You should be able to piece together why there is more noise at a higher ISO by now though:
>> Anonymous
(guldarn field was too long TWICE. I need to write less)

- at ISO 100, this noise (which is pretty tiny) is drowned out by the massive amount of light coming in the lens. The noise is there but you don't see it.
- As you go up in ISO, the amount of light coming in decreases but the noise remains constant. So the signal-to-noise ratio goes up.
- Also as you go up in ISO, you start amplifying whatever was in the photon wells -- no way to tell if it was noise or signal.
- So by the time you get to ISO 3200, you've multiplied everything in the well by 32 times. The signal is so small that it's on almost the same level as the noise, and you've multiplied everything by the same amount...so your image disappears in a fuzz of noise.

Hope that helps.
>> Anonymous
>>265602
good explanation
>> Anonymous
I should add one line to this long thing, since you were asking for a simple way of explaining it:

say "Turning up the ISO is line turning up the volume on a stereo...you start to hear little pops and hums and hisses that aren't in the original recording, but it lets you hear the music where you otherwise wouldn't be able to." It's a physically accurate analogy and it's easy to understand.
>> i - !EoFJjFcCco
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>>265600
>>265601
>>265602
>> Anonymous
>>265602Hope that helps.

i lold
>> Anonymous
>>265609
Ironically I do have a beard somewhat similar to the one in the picture.
>> Butterfly !xlgRMYva6s
>>265600
>>265601
>>265602
Awesome, thanks. Interesting read too.
>> Anonymous
>>265644

Butterfag didn't even know that? Hahahaha.
>> Anonymous
>>265621

Thanks Anon, good read.
>> Anonymous
>>265601
>Simple. Sensors are sensitive to more than just visible light.

So the advancements in lower noise and higher sensitivities come from developing ways to make the sensor less sensitive to non-visible light?
>> Butterfly !xlgRMYva6s
>>265732
Wat.

Interesting read = well written
>> Anonymous
>>265755Interesting read = well written

nice save, except not
>> Anonymous
>>265600
Hero anon is hero.
>> Anonymous
ET MAKES SHIT BRITER