ISO speeds and noise

[Raaf Hornet]

Hi, Im not sure if this is the correct section for this question, but I keep reading about when you up the ISO speeds on a DSLR, the shutter ? noise increases. How does this affect taking the picture. Thanks for any answers, jeff

[Tannin]

Hi Raaf,

We are not talking about "shutter noise" here (as in the sound you hear when the shutter goes off). We are talking about digital noise - the visual equivalent of what in radio we call "static". It is similar to the grain we used to get in film days. (And different from film grain in certain ways also, but these need not concern us here.)

In reality, noise does not actually increase at all at higher ISOs, but it seems to. What actually happens is that there is always a certain amount of noise in every shot, but at low ISOs it is drowned out by the signal. You can't see it.

As you increase the ISO, you are getting fewer and fewer photons hitting the sensor (less signal) but still the same amount of noise. Because there are so few photons hitting the sensor now, the noise is higher in proportion, and we can see it.

It is exactly the same as listening to the radio. Drive from the centre of Melbourne out to Keilor and tune in 774 on the radio. You will get a great signal, no noticeable noise at all, because you are only a kilometre or two from the transmitter. Now drive to Mildura. You can still pick up 774 (just), but the signal is very faint, and you have to turn the radio up loud to hear it properly. But in amplifying the faint signal, the radio is also amplifying the noise (which is the same as it was in Keilor) so the sound quality is now poor.

[Raaf Hornet]

Thanks Tony for explaining it in simple terms, very helpful mate

[bigdazzler]

so ... shoot at the lowest ISO you can whenever possible to avoid that ugly graininess that noise produces.

Noise can be kinda cool too though ... have a look at this image, this was at ISO1600. You can kinda replicate old grainy film like pictures.

[I @ M]

Mr. Hornet, Tony summed it up very clearly but I would like to add one hint to avoiding noise when you have to use a higher ISO than you would prefer to use.

Avoid underexposure as much as possible as the noise / grain that is produced in dark areas is harder to deal with than slightly overexposed areas.

And thanks Tony, now I know why I get noisy photos, we don't get 774 down here at all, we have to go to a higher frequency of 828.

[OzzieTraveller]

G'day all

Raaf - an excellent Q
Tony - an excellent answer

and for all the Melb ABC 774 listeners ... travelling from N'castle thru Sydney last week, I was listening to 774 loud & clear ... dunno how it got that far, but it was better reception than ABC 1332 N'castle & equal to ABC 594 Sydney

Regards, Phil

[Tannin]

^ must have been listening on your D3.

[yarnella]

Tony,
Many thanks for the clear explanation. I am a techo and like to know what goes on behind the scenes...and now I know.

Thanks again.

[Scotty72]

Though on a slightly different focus this thread may be worth your while reading (especially the first half).

Scotty

[etherial]

Another good place to look is in the new to photography forum.

Here is the thread on ISO.