ISO and DR

[Sabaki]

hey everybody

Quick question: Does ISO affect dynamic range or more specifically, do higher ISO affect DR negatively?

If so, how does ISO 50 compare to ISO 100?

 

[bdunbar79]

Of course, higher ISO typically decreases DR. Noise = SQRT (#photons)

If ISO 50 is not analog, then it is simply an ISO 100 shot pulled one stop. DR should be the same.

 

[Mt Spokane Photography]

Few cameras have a real ISO 50. If you take the base ISO of 100 or sometimes 200, and compare it to ISO 1600, the DR will be reduce substantially. At 25600, it gets to the point where you must be careful to get a good exposure.

 

[9VIII]

Dynamic range is determined by the accuracy with which electrons can be counted (after the photocell does its magic and turns photons into electrons), after being translated from voltage to digital information each count of electrons is given a value as a shade of light.
Increasing ISO by one stop basically applies the full brighness value to half as many electrons. With half as many electrons to count the total number of different shades goes down.
It's not quite linear though as read accuracy goes up as less electrons are being counted, so you end up with dynamic range going down slowly rather than being split in half every time.

http://www.sensorgen.info/CanonEOS-1DX.html
http://www.sensorgen.info/NikonD810.html

Here you can see at ISO 100 the 1DX has almost twice as much read noise as at ISO200, but the D810 doesn't increase read noise significantly at low ISO, thus the huge DR boost... Which would mean more to most people if our display technology could show more than the equivalent of 8 stops at a time.
(which is just another example of old standards sticking around way too long)
Recording more than 8 stops lets you protect highlights and recover exposures that were less than ideal, but unless you're using a display method with 10 or 12 bit colour, (do printers have that capability?) it's still impossible to view more data on the same picture.
Knowing how much range is available is also useful for setting an upper limit to ISO on your device, for example we know that the 1DX gives 8 stops of DR up to ISO 25600, still saturating the capabilities of a normal computer display, but beyond that you lose more and more visible information.
Camera companies mostly include extremely high ISO options just for bragging rights or the odd time you just want to get a license plate number at night.

 

[adventureous]

This what CPN Europe says about iso 50 on a 5d mark ii " By default the EOS 5D Mark II has an ISO range from 100 to 6400. However, switching C.Fn I -3 to option 1: ‘On’ will allow access to the expansion settings – ISO 50, ISO 12,800 and ISO 25,600, which are named L, H1 and H2 respectively.

These settings should only be used when you really need them, as the image quality will not be as good as at the other ISO settings. However, there is no harm in enabling the setting, so you may as well leave it turned on, unless you don’t want to even be able to accidentally select the higher or lower settings."

My experience on a 5dII is iso 50 looks bad.

 

[Sabaki]

You guys are seriously smart!

Thanks everyone, really appreciate the feedback