ISO Relationship

[laawaaris]

I am trying to get my head around the ISO relationship to Aperture and Shutter Speed.

My camera has four ISO settings - 200, 400, 800, & 1600.

When I move one stop from 200 to 400, it "appears" to let more light into the camera and the overall foto appears brighter.

What is the equivalent of moving from ISO 200 to 400 with Shutter Speed? If my shutter speed is at 1/100, how many stops do I have to slow the shutter down by to get the same brightness kick as moving from ISO 200 to 400 gives you?

The same question applies to Aperture. If my Aperture is at f/8, how many stops do I have to open the Aperture up by to get the same brightness kick as moving from ISO 200 to 400.

[JohnT]

Off the top of my head:

Tv 1/100 --> 1/60 = full stop equivalent to ISO 200 --> 400.

Av F8 --> F5.6 = full stop equivalent to ISO 200 --> 400.

You can take some shots to test this. I'm sure someone will correct me if my math is wrong.

[AndrewCCM]

What John said.. It's pretty much the same across the board..

1 full stop = double ISO = shutter speed (full increments)

F8 1/500 ISO 200 = F8 1/250 ISO 100 = F5.6 1/250 ISO 50 = F5.6 1/500 ISO 100

[laawaaris]

Ok, I will test this out today,

BUT what about the other ISOs - is it basically a 2-stop difference each time you move up?

So basically, if you jump from ISO 200 all the way up to 1600, moving four ISO stops, is that equivalent to moving 8 shutter stops slower, or 8 aperture sizes larger?

So does this extrapolation make sense?

Tv 1/100 -> 1/15 = full stop equivalent to ISO 200 ---> 1600
Av F/8 -> F/2.8 = full stop equivalent to ISO 200 ---> 1600

(I just shot a wedding entirely in ISO 1600 by mistake. The color of the photos is gorgeous and some of the shots I took are the best I have ever taken. Unfortunately, all the photos have grain all over the place - even if the peoples nostrils. All the photos look like they are drawings and not pictures).

[AndrewCCM]

Going from ISO 200 - 1600 is 3 Stops

200 - 400
400 - 800
800 - 1600

Doubles each time.

[AndrewCCM]

Shutter increments:

1/15 - 1/30 - 1/60 - 1/125 - 1/250 - 1/500

Each represents a stop of light.

[laawaaris]

My Nikon D50 has different shutter stops:

1/500, 1/400, 1/320, 1/250, 1/200, 1/160, 1/125, 1/100, 1/80, 1/60, etc

I understand the mathematical reason however to simply cut the stops in half (1/500 then 1/250).

Are you saying that if I let in twice as much light by going from 1/500 to 1/250 - it is the same as going from ISO 200 to ISO 400?

[AndrewCCM]

Yes. It is the same for "exposure". Now the difference lies in the ability to stop motion. Ie, fast shutter freezes more motion. It's all a relationship... Similarly F5.6 lets in more light than F8, but gives you shallower depth of field, but using differing shutter speeds or ISOs in combination will result in the same "exposure".

The other shutter speeds you mention there are increments.. typically in 1/3 stops.

Hope this all helps a little.

[laawaaris]

On a related note, what is going on in the camera that makes the pictures grainy when you climb up to ISO 1600?

I understand there is a shutter and a littley peephole for the aperture (kind of like our eyes work). Sometimes I squint and look at things to see how a camera would look at them.

But what exactly is happening in the camera when I switch to a higher ISO?
1) Why does the picture become brighter?
2) I understand ISO to be "sensitivity to light" - but is there an actual mechanical device in
the camera that is moving, shifting or changing to set the ISO up?
3) Where does the grain come from? Is it making up information about the pixels when it
records to the sensor. If so, why does it choose to use "grain" rather than closely
approximating the values from the pixels that are surrounding it.

[AndrewCCM]

Think of ISO in digital as basically a signal boost. Everything boosted gets an amount of noise associated with it. Some camera sensors (and/or onboard processors) deal with ISO noise better than others. Maybe think of boosting ISO as taking a picture into Photoshop or whatever and boosting the brightness. It gets brighter, but the picture gets grainy/noisier.

High ISO performance is one of many things to consider depending on how and what you shoot. You'll see all kinds of comments on certain brands and models performance with higher ISOs.

The key with higher ISO, is to make sure you are not underexposed. If you are and you subsequently have to boost it more in your post processing, the noise with become even worse.

I shoot a lot of low light weddings, events, concerts, etc... and moved from D70's to various Canons over the years. My best performing high ISO camera body is the Canon 5D.

But.. consider faster (F2.8 or better) glass too. High ISO performance doesn't substitute good faster glass, but helps in situations where you need it.

I try and shoot at the sweet spot ISO wise (as low as I can for the settings that I want). If I want a lot of ambient/natural light, I'll boost the ISO if necessary to a point. You'll have to become familiar with the ISO noise characteristics of your camera and make whatever tradeoffs necessary to get the exposure and quality you desire.

[Reuel]

Electronically, you can think of the ISO setting as controlling an amplifier that's in between the sensor and the analog-to-digital converter. It amplifies everything from the sensor, including noise. Bigger ISO == more amplification == more noise.

[*Mike*]

I'm actually putting together an illustrated ebook on this stuff... one part is the relationship between ISO, SS, and aperture. I'm not quite done yet, or I'd sent it along to you. I'm going to be teaching a basics of digital photography class this spring through the city, and I thought that a reference would help people - especially if it had pictures!

[brad]

Mike - I've been teaching a similar class.. you're welcome to my notes if you want to see the subjects and the order in which I discuss them.

[David Whatley]

Me to, i'm also ISO Relationship.
In Search Of Relationship, or at least that was my thought when I read the title.
LMAO

[Cerbera LM]

Shows the relationship between the aperture, shutter and iso. www.pbase.com/wlhuber/the_basics