Sweetest ISO for the T2?

[John Vincent]

Just watched the Zacuto DSLR shoot out part 2. In it, the DPs explained that every DSLR camera tested had an "ISO sweet spot" where there would be less noise then at other ISOs, even if they were higher ones.

Essentially meaning that if you could properly light at that ISO it would have the least amount of camera generated noise.

Does anyone know what that ISO is for the T2 or how you'd test this? Thanks -

john

[Fergus Anderson]

If the native ISO is 160 then 200 ISO might be the cleanest?

[James Donnelly]

Originally Posted by John Vincent

Just watched the Zacuto DSLR shoot out part 2. In it, the DPs explained that every DSLR camera tested had an "ISO sweet spot" where there would be less noise then at other ISOs, even if they were higher ones.

Essentially meaning that if you could properly light at that ISO it would have the least amount of camera generated noise.

Does anyone know what that ISO is for the T2 or how you'd test this? Thanks -

john

You cannot escape the fact that in reality, higher ISO means more noise.

On the 5d mk II and 7d, there are 'intermediate' ISOs values which at first glance, look like they offer lower noise, but really they are under/over exposed versions of the standard values. A useful feature for managing shadow / highlight detail, but not one which defies the laws of physics.

If you plotted ISO noise against true ISO value for any sensor, you would clearly see noise going up with ISO.

Likewise, you would see dynamic range going down as ISO goes up.

The long and short is, on the T2i, ISO 100 has the least noise and the most dynamic range.

[John Vincent]

"You cannot escape the fact that in reality, higher ISO means more noise"

Well, you'd think so, but they clearly indicate that's not the fact:

The Great Camera Shootout 2010 - Film Vs DSLR Comparison | Zacuto

Interesting idea about 200 being the best ISO...

jdv

[James Donnelly]

Originally Posted by John Vincent

Well, you'd think so, but they clearly indicate that's not the fact:

The Great Camera Shootout 2010 - Film Vs DSLR Comparison | Zacuto

I saw that video before I got my camera, so I can't remember exactly what they said.

There are sweet spots in ISO in some ways. For example, ISO 100 and 200 often have similar noise and dynamic range levels, even though 200 captures double the light. However, I repeat what I said, when ISO goes up, so does noise. It can't go down.

I agree that it seems to be the case that this CAN happen, but I will try to convince you that it's in fact not really happening.

Here are the intermediate ISO values that seem to be ISO 'sweet spots', or 'better than their lower neighbor on the dial':

160, 320, 640, 1250

These values are not true ISO settings on the sensor. They are respectively set on the sensor at:

200, 400, 800, 1600

There is then applied a 1/3 stop reduction in exposure. If you were to analyse the latitude for highlight detail in these 'ISOs' you would see that it is inferior to other values.

Likewise, lets take the intermediate ISO values that seem to give more noise than the others:

125, 250, 500, 1000, 2000

These values derive from the sensor being set at respectively:

100, 200, 400, 800, 1600

with a 1/3 stop over exposure being applied. In this case, you will see less shadow detail.

In other words, as I stated before, these settings are a convenience for managing exposure, and do not give something for nothing in ISO terms.

By the way, there is no such thing as 'native' ISO as such. ISO in DSLRs is simply the gain, or power applied to the sensor. ISO is used as a convenience term in stills cameras to give continuity to film users

Let's not forget, these intermediate ISOs are not available on the t2i, but as I have indicated, you are not really missing anything.

If you want to confirm that there is a one way relationship between gain and noise, see the DxO test for the T2i:

EOS 550D

[John Vincent]

Hey, good stuff James - thanks for the info...

So you'd shoot at ISO 100 all things being even?

jdv