Can someone explain ISO settings?

Post by **Big Kev** » Tue Dec 12, 2006 2:03 am

What are they, what do they do and what difference do they make to what you're shooting?

Post by **norbs** » Tue Dec 12, 2006 2:59 am

ISO is basically a measure of a films/sensors sensitivity to light. A lower number, 100, is less sensitive than 1600.

http://www.dpreview.com/learn/?/key=sensitivity

http://www.photoxels.com/tutorial_iso.html

Nigel · Post by **Nigel** » Tue Dec 12, 2006 7:44 am

ISO settings are the equivilant of film speeds. 100 ISO = 100 ASA etc etc. The higher the number, the faster the film / capture

Post by **Big Kev** » Tue Dec 12, 2006 7:59 am

fourthof5 wrote:ISO settings are the equivilant of film speeds. 100 ISO = 100 ASA etc etc. The higher the number, the faster the film / capture

Yeah, see that means nuthin to me

I'm from 'point and shoot' land.

What effect does a different ISO have on a particular shot. Close up, sunny, dark, moving objects etc.

Post by **Shonky** » Tue Dec 12, 2006 8:22 am

Higher ISO is generally used for darker situations, but for digital cameras longer shutter time or wider apeture is preferable to a higher ISO setting.

My understanding from what I've read many moons ago, higher ISO in digital cameras is a fudge as it just amplifies the signals from the sensor, and therefore also amplifies any noise present as well, which results in visible noise and grain in photos taken.

Bear in mind I'm still a newb to this stuff, so my interpretation maybe off, is it Nige and Norbs?

pab · Post by **pab** » Tue Dec 12, 2006 8:23 am

OK, the more sensitive the film/sensor the brighter the image will be (for the same exposure), essentially you need less light to create a bright image.

What this means to you is that a higher ISO will allow you to use a faster shutter speed for a dark scene (so if you are taking a photo in the evening and don't have a tripod raising the ISO might allow you to still get a sharp picture because it will allow you to use a faster shutter speed). It is also useful when taking phots of fast moving objects, like say, just to pick a random example, a race car. It will allow you to use a very high shutter speed so that it is very sharp (if that's what you are after, the problem with using a fast shutter speed for cars is that it looks like their standing still, not really the effect you usually want).

There is of course, always a trade off for these sort of things, and the downside of using a high ISO film/sensor setting is film grain or noise. The more sensitive the light capture device is the more likely you are to get areas of noise or grain.

What this means is that if you don't have enough light in your scene to use the shutter speed and aperture settings that you (or the camera) wants to use, you could try increasing the ISO setting, but you should always try to keep ISO as low as possible to make sure your pictures are as clean and smooth as possible.

Hope that helps.

PB.

limbo · Post by **limbo** » Tue Dec 12, 2006 8:25 am

iso is the 'speed' of the film... its light sensitivity.
the higher the iso the less light you need to capture the image.

the amount of light falling on the film is governed by the shutter speed and the aperature.
shutter speed is reasonably self explanatory,... the faster the shutter speed the faster the action you can 'freeze'
that is with say a shutter speed of 1/250 you can freezw the action of a running man.. slower and he will have a blurred outline as he moved whilst the shutter is open... the slower the shutter speed the more image definition is captured..

apature is the little hole in the lens that thelight goes through... the higher the fstop (aperture) the smaller the hole and conversly the lower the aperture number the larger the hole.. allowing more light through in that 1/250 shutter instant.

the higher the aperture the MORE depth of field (DoF) DoF is basically the focal distance of the THAT LENS at that fstop.

so i higher DoF will put objects in the background in focus as well.. a lower one will only have the image subject in focus..
take i low fstop image of a foreground subject and a high fstop of the same subject and study the two images.. DoF becomes apparant then.

ISO governs the light sensitivity... with high iso i can therefore have a small aperture (high fstop) and a fast shutter speed in low light situations. but.. ther is a 'con' as well...
the higher the iso the more 'grainy' the image will be... graininess is that 'mottled' effect that happens when you shoot in low light situations...

i can probably make it clearer if you clarify where you dont understand my ramblings....

all this refers to silver halide (traditional) film and not digital cameras. although our little canon A510 digicam has a grainy effect the same as film.

limbo · Post by **limbo** » Tue Dec 12, 2006 8:26 am

ROFL
i gotta learn to type faster

Nigel · Post by **Nigel** » Tue Dec 12, 2006 8:34 am

Thats pretty close limbo. Apature is a bit of a bastard to get to know, The highter the number the smaller the apature

Large Opening.................................Small Opening

f1 f1.4 f2 f2.8 f4 f5.6 f8 f11 f16 f22 f32 f64 f90

The higher the ISO / ASA rating the grainer the image so ISO 800 is pretty noisy, while ISO / ASA 100 is noisless.

Post by **norbs** » Tue Dec 12, 2006 1:35 pm

fourthof5 wrote:Thats pretty close limbo. Apature is a bit of a bastard to get to know, The highter the number the smaller the apature

Large Opening.................................Small Opening

f1 f1.4 f2 f2.8 f4 f5.6 f8 f11 f16 f22 f32 f64 f90

The higher the ISO / ASA rating the grainer the image so ISO 800 is pretty noisy, while ISO / ASA 100 is noisless.

ISO 800 is pretty noisy? Not on most Canon's it isnt. 1600 maybe, but even that is quite good on the 30D

Nigel · Post by **Nigel** » Tue Dec 12, 2006 1:48 pm

Thats true. But I didn' t think he had a Canon. Mind you I don't always think noise is a bad thing. Some images actaully look better with some grain.

Post by **norbs** » Tue Dec 12, 2006 2:03 pm

I always thought noise and grain were 2 different beasts.

Noise comes from the camera amplifying the signal from the sensor and some pixels send a slightly different value through.

Grain. Well I thought it was a by product of the emulsion of the film.

I may well be wrong on both accounts.

limbo · Post by **limbo** » Tue Dec 12, 2006 3:22 pm

norbs wrote:I always thought noise and grain were 2 different beasts.

Noise comes from the camera amplifying the signal from the sensor and some pixels send a slightly different value through.

Grain. Well I thought it was a by product of the emulsion of the film.

I may well be wrong on both accounts.

You are correct norbs noise is a product of 'digitalicality'
and grain is an emulsion thing.. grain is actually the silver halide particles in an emulsion film. to be more light sensitive they need to be larger and they do tend to 'clump' during processing.. the clumping becomes more noticable when the halide particles are larger.

grain can be used to good effect in a photo, some photogs have made a carreer out of producing grainy shots.

Nigel · Post by **Nigel** » Tue Dec 12, 2006 3:47 pm

Film has grain, Digital has noise. In both cases they can be the same thing, hence my lobbing them together. noisy digital shots, if done well, can, as limbo has highlighted, be used in the same way film grain, to really give an image a spesific feel. Indeed, of late I have found myself liking a bit of grain in my images.