A Question of ISO
Hi All.

Only last week I managed to talk the Mrs into letting me buy the Canon G9 - i've been reading a lot about all the different settings and starting to understand what all the technical terms means..

Whilst I do understand what ISO means I dont quite get it. I read that the higher ISOs, the more noise you introduce into the shots. The question is why does my G9 goes up to ISO1600? - why would I ever need to use such a high ISO if I'm going to get lots of noise in the shot?.

Thanks for your comments..

Comments (12)

Deez_nutts wrote:.

Why would I everneed to use such a high ISO if I'm going to get lots of noise in theshot?.

It is sort of an artistic thing, called "available light". In the old days, some film photographers would shoot ISO 400 Tri-X film exposed at ISO 2400 or such, and then process in exceptional film developers that could pull an image out of it. Fast film speed for available light photography without flash. It was very grainy, which was deemed acceptable, even sometimes desirable as an art form. Digital noise appears much like the film grain did, and for much the same reason..

Digital cameras with larger sensors can shoot higher ISO with less noise than the tiny sensors. And this is a plus, to be able shoot available light without flash. And it is coming, with affordable full frame size sensors someday, and it will be truly useful when the noise becomes minimal. Some people crave this, and others have no problem with the concept of adding more light...

Comment #1

Because the amplifying the noise is just an unfortunate byproduct of amplifying the entire signal from the sensor. It effectively makes the sensor more sensitive so not as much light has to hit it. This means that shutter speeds can be faster with a high ISO..

So when a camera is handheld, if the light condtions (and maximum aperture) at ISO 100 mean that a shutter speed of say 1/5 sec is needed, that is going to cause problems as few people can hold a camera totally still for that long. But increasing the ISO to 800 or 1600 means a faster shutter speed that is achievable handheld for many photographers..

Similarly increasing the ISO can allow a sports photographer to get a shutter speed of 1/500th sec which he may feel is the minimum to freeze sports motion, while at ISO 100 he might only get a much slower speed, leading to blurred shots..


Comment #2

If i've understood the above posts correctly I'm I right in thinking that higher ISO only comes into play when shooting in low light condition without a flash?.

Is the shutter speed related the ISO level?..

Comment #3

When the choice is noise or no picture you do what you have to for a picture...

Comment #4

Deez_nutts wrote:.

If i've understood the above posts correctly I'm I right in thinkingthat higher ISO only comes into play when shooting in low lightcondition without a flash?.

Usually yes. Not sure about the G9 but most P&Ss struggle badly above ISO 400 or even 200 - while dSLRs perform much better, up to ISO 1600 with few problems. The new Nikon D3 allegedly has usable ISO 25000..

Is the shutter speed related the ISO level?.

Yes, doubling the ISO should allow you to use twice as fast a shutter speed. In fact ISO, shutter speed and aperture are all related in this way: doubling the aperture size should allow you to double the shutterspeed or halve the ISO. These common increments are called stops..


Comment #5

As this is the beginners forum I'll assume you are a beginner. In which case I'll add that for most of us the camera can be left on ISO 100 all the time but you'll have 200, 400 etc in reserve and can easily experiment with them. I doubt if you'll need to use more than ISO 200 for normal family or everyday photography. I often take pictures at night and have few problems with ISO 80 or 100 which give very nice pictures. Most of the time my shots are deliberately under exposed to show that it is night, ie with a dark sky. But other may want high speed for sports etc..

Regards, David..

Comment #6

Aperture, shutter speed and ISO (sensitivity to light) are bound together. Aperture (f/stop) regulates the amount of light coming through the lens, shutter speed regulates the length of time the light falls on the sensor and ISO sets the sensitivity of the sensor..

Moving from f/2.8, f/4, f/5.6, f8 reduces the amount of light through the lens by 1/2 for each "stop". Changing the shutter speed from 1/30, 1/60, 1/125, 1/250 reduces the amount of time the light is striking the sensor by 1/2 for each "stop". Changing the ISO from 1600, 800, 400, 200 reduces the sensor sensitivity by 1/2 for each "stop". If one control is set to obtain a specific objective at least one of the other controls must be reset (and maybe both) if correct exposure is to be maintained...

Comment #7

If you want to take a shot at night and the distance to the subject is beyond the range of your flash or if you do not want the flash because it will highlight the photo rather maintain the 'mood' of the shot, you will appreciate the higher ISO speed...

Comment #8

You can use it or completely ignore depending on subjects and lighting situation..

In most situations (at daylight or bright indoor light) ISO 1600 should not be used to not sacrifice detail quality. Use lowest ISO with exposure that you can hand-hold, or tripod + long exposure when shooting static subjects at dim light..

At certain situations when light is very dim but subjects are moving (kids near candle light, life music in evening restaurant) you may want to save feeling of moment, as most important (avoiding flash) and ISO 1600 will still be usable for 4X5 print..

These examples were shot with DSLR that has better ISO performance then your camera, but may give you idea of feeling I'm talking about. (ISO 400 and 800 on DSLR).

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This shot was made with ISO 800 that fail short to stop the dancer - shame on me forgetting to switch to ISO 1600 or ISO 3200 and to AF..

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Anyway, ISO 1600 could be very usable when you desperately NEED IT!!!

Comment #9

David Hughes wrote:.

[...] I doubt if you'll need to use more thanISO 200 for normal family or everyday photography..

I would guess that for compact cameras the most common situation for high ISO is when you want to take pictures in the evening / at night, when you are out in a restuarant, pub, club and you don't want to use the built in flash, to preserve the atmosphere, take a candid picture, or because you want to avoid the "deer in the headlights" look, that can happen very easily with compacts..


Comment #10

Here is an example of using high ISO. I was at Disney's night-time electrical parade. If I used a flash it would have ruined the look. These were shot in JPG with no post-processing. (If I had it to do over, I would have shot RAW.).

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Comment #11

Like they say, a picture paints a thousand words - thanks for all the example shots and all your inputs..

I will now try all i've learnt on my G9...again many thanks..

Comment #12

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This question was taken from a support group/message board and re-posted here so others can learn from it.


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