[luigi]

Originally Posted by sejanus

I dunno about that.

The math sounds impressive but I have some landscape photos where the exposure length was about 2 minutes at 100 iso on my 1ds mk3. There is darn near zero noise in them.

If I did 2 minutes at 1600 iso I can't imagine it would have near zero noise in it.

This photo was 106 seconds ;

http://www.gavincato.com.au/Blogging...verseas025.jpg

This photo was 121 seconds ;

http://www.gavincato.com.au/Blogging...verseas027.jpg

The 100% crops which I can post if you like have pretty much zero noise.

I think you haven't understood what I said.

If you want to minimize noise the key is to expose to the right, in other words get as much light as you can, your first and always preferred way to do this is to increase exposure time.

In all your shots the key to low noise is to just shot at ISO100 with the longest exposure time you can without blowing any channel.

The key is that you shoot at ISO100 not because ISO100 has less noise (it doesn't) but because ISO100 allows you to expose longer!

Now a completely different scenario: Stars. If you don't want trails your exposure time is limited by your focal lenght. Let's say you can't expose more than 20 seconds.

Then you should shoot at the highest ISO you can without blowing any channel for 20 seconds.

The highest the ISO the better the S2N ratio will be.

In short words:

1) Expose as much as you can
2) When you can't expose more if you have room in the histogram increase the ISO

Hope this is more clear now