higher and lower sensitivity

Taking a min, of12 photograph different subjects at different ISO, 100 , 400, or 800 ISO.

In to days cameras After this course was written. Modern cameras have come far. Giving 24,000 ISO extended . you can take photos in almost total darkens. At dusk still freeze moving subjects with out flash.   Noise is apparent . Noise is different from grain. It tends to show colour specks on long exposure. When I used film like Ilford  400 ASA American standard association if I rightly remember. The grain was often used to its advantage with ART form. Some time we used to Over over develop the film to gain grain, for that reason. In todays Digital world . Sadly thats fallen away with everyone looking to pin sharp imaging, High MP camera SLR35mm 21MP and Medium format 40 MP Noise is now being lost in the 800 ISO stage. However on my trusty 30 D at 8 MP
I took these on 100, 400 and 800 ISO hand held, cloudy day and under shelter.

One main advantage against yesterdays cameras and film. The use of a Trypod has become less required.  With amazing high ISO and image stabilising. You can get away holding the camera, and most subjects including shooting sports in low light.
 Nothing can replace the quality of a photograph taken on a solid support.

100 ISO 

30 sec F 4 

800 iso

100 sec F6.3 

Looking at the two above photos. Not to much difference is noticeable. Its only when the enlargement is made you can see any change .

100 ISO

160 Sec F 5

400 ISO

100 sec F 7.1 

With the above also . 400 ISO renders a slight, hardly noticeable difference in the shadow areas or in the detail as I will show later .

100 ISO

1/25th f 3.5

The above photo had better shadow

800ISO

1/80 sec f 5.6 

Even in the shade. Taking these two pictures from 100 to 800 ISO . The print would have to be enlarged, double to see any real difference. With todays cameras, having auto and program modes. As ISO is adjusted , so is the speed and aperture. Later I used Manual mode. 

100 ISO

100 sec 5.6 

800ISO

320 sec f 10

Movement can be over come using higher ISO as the much more higher shutter speeds can be used. And Depth of field has a much wider span.

100 ISO

1/50th f 3.5

800 ISO

1/160sec F8

The only difference here is a paler shade of colour tone, as the pixels like grain become less dense.

100 ISO

1/125th sec F8

800 ISO

1/400th sec  f14 

 100 ISO

1/80 F5

800 ISO

1/250 F9

  100 ISO

1/250 f 10 

 800 ISO

1/640 f16

here a difference can be seen in the shadow area . As the aperture gives more depth , 

 100 ISO

1/50th sec f4.5 

800 ISO

1/125 sec f 7.1 

In lower light levels. also the noise become apparent . 

100 ISO

1/40th sec F4

The lady sat on the left magnified  by 200%

800 ISO

1/100sec F3

The same lady also magnified 200% clearly the noise Just like grain in a film is much grater.

100 ISO

800 ISO

100 ISO 

1/250th F9

Magnification x 200 

 I notice with the lower ISO that the sea here looks much denser, with out adjustment contrasty

800 ISO

1/800 th f14 

Now you see how much higher speed is required to freeze action,And can be used, and giving greater depth .  

So over all, ISO makes the use of aperture and speed more flexible. Draw backs, If you want to make big prints or drastic cropping. You do need to use lower ISO  Best to use a Try Pod, and images will become sharper and more detailed. 

Soon ISO will just be another method of adjustment, and noise will be a thing of the past. So grainy fuzzy photos for effects will be left to filters.