5d extended iso settings... curious question

[trothwell]

This probably has no impact whatsoever on life, the universe, or

anything, but I was just curious...

 

On the 5D, why are the extended ISO settings (L/50 and H/3200) turned

off by default, activated by a custom function?

 

This seems to me to be something that users would want to have

available all the time, and I don't understand why it would be in a

custom function. Why not always on? Or, why not put, say, ISO 320

into a custom function?

 

Again, no big deal, just curious if anyone knew. :-) :-)

[bobatkins]

ISO 3200 increases noise, ISO 50 reduces dynamic range.

 

Putting them in CFs reduces the number of complaints about noise and dynamic range issues from users who don't really have much of a clue about digital cameras.

[jon wilson]

From what i understand they aren't true ISO/ASA values so they are not on by default...but i

could be wrong

[nels]

"ISO 50 reduces dynamic range"

 

How so, as compared to ISO 100?

[mormegil]

From what I understand, at ISO 50, you loose about a stop of dynamic range in the highlights. But it does have even less noise than ISO 100.

[nels]

Is that true even if you shoot RAW?

[jespdj]

ISO 50 and ISO 3200 are not "true" ISO settings.

<p>ISO settings between 100 and 1600 are harware settings on the sensor. By changing the ISO, you set the gain of the amplifiers in the sensor (higher ISO = higher gain setting, which makes it more sensitive, but also increases the noise).

<p>ISO 50 is a "trick": the sensor is actually set to ISO 100 and the camera overexposes by 1 stop, and then processes the data that comes from the sensor to compensate for the overexposure. The result is that you loose 1 stop of dynamic range in the highlights.

<p>Likewise, ISO 3200: the sensor is set to ISO 1600 and the camera underexposes by 1 stop, and compensates for this by digital processing. You loose one stop of dynamic range in the highlights.

<p>You can do exactly the same "by hand" if you do this: shoot at ISO 100, deliberately overexpose a stop, compensate for the overexposure on the computer (and vice versa for ISO 3200).

<p>And yes, this is even true if you shoot RAW.

<p>If you want to hear it from a Canon director himself, check out <a href="http://www.digitaljournalist.org/issue0604/westfall.html">Chuck Westfall's Tech Tips</a>:

<p><i>"There is about a stop less dynamic range in the highlights at ISO 50, which is the reason why this setting is normally locked out."</i>

[nels]

Well, you always learn something new. Thanks.

[peter_white2]

There is not less noise at ISO 50 than at ISO 100. Noise is the same, essentially, there is no noise.

[luis alvarez torres]

In That case the 50 setup will help by not having to use a ND filter in the certain cases that it would normally be needed. Or not?

[luis alvarez torres]

If you want to make an image with a shallow depth of field but the lighting conditions at ISO 100 will make you use F4, then changing to ISO 50 will let you use F2.8 and give you the depth of field desired. Am I wrong?