Aperture and ISO speed

workaccount

Hi,
I know aperture and ISO are two completely different things (technically) and I'm relatively new to photography so I haven't done many experiments but does aperture and iso do more or less the same thing.

ie. More light or less light.

helios

No. Iso is the sensitivity of the film or sensor, while aperture is the size of the opening of the lens

workaccount

helios wrote: »

No. Iso is the sensitivity of the film or sensor, while aperture is the size of the opening of the lens

I know...I said they were two different things technically but it's less light or more light at the end of the day isn't it? ie. higher iso sensitivity means more light.

CabanSail

There are two settings that dictate the amount of light reaching the Film/Sensor, they are Shutter Speed & Aperture. Each has secondary effects. The Larger the Aperture Setting (Lower F number) the shallower the depth of field will be (How much of the image is in focus) The faster the shutter speed the more it "freezes" the movement, slower shutter speeds will allow movement to blur.

Once the light has reached the Film Plane or Sensor then the sensitivity to light (ISO Setting or Film Speed) comes into play. The more sensitive the Silm (Sensor or Film ) the more Noise or Grain becomes an issue. The better quality of the Silm the better it will perform.

Correct exposure is a combination of all three of the settings (plus the use of Filters) to achieve the result you want.

As to the the ISO & Aperture question asked. At a fixed Shutter Speed, a Higher ISO will allow you to use a smaller Aperture setting & hence get a larger Depth of Field, but you may find the image getting more Noise.

There are no "right" settings as each different combination will give alternate images. You just need to gain an understanding of them all & then make a decison as to how you want your image to appear.

ThOnda

ISO and Aperture in detail.

amcinroy

No that's not correct I'm afraid workaccount

ISO Sensitivity is nothing to do with the exposure (or amount of light) which is defined purely by shutter and aperture.

Sensitivity is sometimes treated as an exposure control and it is conveniently expressed in "stop" notation but it is actually more to do with the amplification of the signal (exposure) by the sensor. Nothing to do with more or less light.

But of course, higher sensitivity ISO might allow you to work with less exposure so the three controls (shutter, aperture, ISO) do go hand in had. But to re-iterate, ISO is nothing to do with exposure although it is part of producing a correct exposure.

CabanSail

amcinroy wrote: »

No that's not correct I'm afraid workaccount

ISO Sensitivity is nothing to do with the exposure (or amount of light) which is defined purely by shutter and aperture.

Yes & No.

I learned all this theory long before there was Digital. The Film Speed ISO is part of the Exposure Equation is it dictates the correct amount of light for that Film. When working with Sensors you have the luxury of changing that sensitivity, but the theory is the same & all the variables are part of correct exposure.

smelltheglove

The way I would explain it, as I'm not into big technical words - silly me, is that by increasing the ISO you let in more let but this can cause more noise.

Aperature wise, again not technical, if you have 5.6f you will get more let but less detail, i.e. a portrait shot of a person with perfect detail but something a couple of feet behind is blurred. If you go to say f20 you will have a lot less light but the majority of the frame will be clear and sharp.

In the end I decide what my preferred aperature is first and then adjust shutter speed and iso as well as I can to get that ap in. Sometimes you have to compromise. I highly recommend trying the manual setting and getting used to this setting as it will result in better pictures. I've only gotten the hang of it recently myself so that is why I still have a childish way of explaining it.

Thats my dumb ass way of describing it! Hope it helps.

CabanSail

smelltheglove wrote: »

The way I would explain it, as I'm not into big technical words - silly me, is that by increasing the ISO you let in more let but this can cause more noise.

No.

Changing the ISO doesn't let in any more light. It just makes the Sensor more sensitive to the light that is there.

It's a bit like having a Singer with Microphone & you turn up the Volume on the Amplifier. The singer is still singing at the same volume but will now sound louder, but so will any noise.

ThOnda

Why would you like to listen "Singer"...?

Maybe some kind of industrial-techno?

Yes, I do agree with explanation. ISO is the sensitivity of the media (film/chip). ISO, Aperture and Shutter speed define Exposure. And the creativity is to alter all three variables to achieve the required picture.

CabanSail

I think that's got it all sewn up now!

AnimalRights

fcking stitch up... :mad:

CabanSail

Well it is an interesting Thread

melekalikimaka

interesting 'thread'

mehfesto2

My way of rememering ISO:
High Iso for Hardly any light
Low Iso for Loadsa Light

Works for me. Well, sort of.
Colour balance is my big downfall.

CabanSail

melekalikimaka wrote: »

interesting 'thread'

I don't want to Needle you but I got there first.

melekalikimaka

good one

that had me in 'stitches'

smelltheglove

Whats with all the puns? God I'm slow on that front I can't think of one. Thanks for the correction cabin - as I said not very technically minded I just know how to get it to do what I want not the inside details.

It's like the Homer explaintion every time I learn something new something old falls out!:o

ThOnda

Actually, it is very simple. If you could read "Understanding Exposure", it is explained in very nice and easy way in that book. Highly recommended for people who are not interested in technical part of photography.

CabanSail

It's all part of the Rich Fabric of Photography.

Stephen

+1 on Understanding Exposure. Great book and its not all that long.

daycent

mehfesto2 wrote: »

My way of rememering ISO:
High Iso for Hardly any light
Low Iso for Loadsa Light

Works for me. Well, sort of.
Colour balance is my big downfall.

Why does everything have to be arseways in photography? Nothing means what it sounds like

pete4130

ISO and aperture can be said to do the same thing but in different ways....
For example going from ISO 800 to ISO 400 you are cutting the amount of light for a certain exposure (aperture & shutter speed remaining the same) in half.

By closing your aperture from f4 to f5.6 you are reducing the amount of light in half for a certain exposure (shutter speed & ISO remaining the same).

The BIGGEST difference with closing (or opening) the aperture is the effect on your depth of field (how much of the foreground & background is in focus.

The difference with changing you ISO is how much more (or less) noise you'll see in the image.

So yes, in effect they can be said t do the same job but in very different manners.

Does this make sense to anyone??

workaccount

pete4130 wrote: »

ISO and aperture can be said to do the same thing but in different ways....
For example going from ISO 800 to ISO 400 you are cutting the amount of light for a certain exposure (aperture & shutter speed remaining the same) in half.

By closing your aperture from f4 to f5.6 you are reducing the amount of light in half for a certain exposure (shutter speed & ISO remaining the same).

The BIGGEST difference with closing (or opening) the aperture is the effect on your depth of field (how much of the foreground & background is in focus.

The difference with changing you ISO is how much more (or less) noise you'll see in the image.

So yes, in effect they can be said t do the same job but in very different manners.

Does this make sense to anyone??

So is the purpose of ISO to increase light if you you want a low aperture but at the expense of noise?

amcinroy

workaccount wrote: »

So is the purpose of ISO to increase light if you you want a low aperture but at the expense of noise?

Sorry workaccount, I think I see what you are getting at but your notation is very confusing.

What do you mean a low aperture? It is better to talk in terms of wide/narrow aperture or high/low f stop. Don't intermix your notation.

ISO does NOT increase light so don't think of it in those terms at all.

The purpose of ISO is allow flexibility in the shutter and aperture combination to yield a "correct exposure". ISO makes the camera more sensitive to light and therefore, as an examples

boosting ISO allows you to work with shorter shutter speeds to achieve a 'correct exposure'.

boosting ISO allows you to work with narrower apertures to achieve a 'correct exposure'.

reducing ISO allows you to work with longer shutter speeds to achieve a 'correct exposure'

reducing ISO allows you to work with wider apertures to achieve a 'correct exposure'

CabanSail

workaccount wrote: »

So is the purpose of ISO to increase light if you you want a low aperture but at the expense of noise?

The Light reaching the Sensor (or Film) is set by the Aperture, Shutter Speed & Filters. Once it is there the ISO determines how that light is recorded.

Try this analogy.

If you have a Tap & you want to fill up a bucket with water.

The more the tap is open, the more water you will get (Aperture)

The longer the tap is open, the more water you will get (Shutter Speed)

If the bucket is has a capacity of 5 litres you will need more water to fill it (Low ISO) but if the bucket has a capacity of 1 litre then it needs less water (High ISO)

Does that make sense?

ThOnda

Reminds me "bees" from Understanding exposure :-)
Nice one.