Dynamic Range EV to ISO Setting; FF vs DX Mode Difference

[ThomasAdams]

Hello,

 I was referencing a link that Jan Anne (if memory serves me correctly) had referred to in a post and I subsequently bookmarked. I am curious why using DX mode drops the DR EV to ISO rating on the same cameras? Obviously there is more here than just "cropping the image". This also leads me down a path of questioning whether the entire image sensor is still active and collecting data, or are the cropped sensors area just "off"?

      reference: https://www.photonstophotos.net/Charts/PDR.htm#Nikon%20D3,Nikon%20D3(DX),Nikon%20D3X,Nikon%20D800E,Nikon%20Z%207II,Nikon%20Z%207II(DX)

Regards,
Tom

[David H. Hartman]

Here is a graph showing Nikon Z7 (FX), Z7 (DX) and Z7 II (FX). It's easier to see the 0.9 dynamic range loose for the DX image using the same image sensor.

https://www.photonstophotos.net/Charts/PDR.htm#Nikon%20Z%207,Nikon%20Z%207(DX),Nikon%20Z%207II,Nikon%20Z%207II(DX)

DX gathers less light than FX because there is less surface area gathering light. Does that explain the loss of DR? I don't know.

Dave

For some strange reason the link offered will not show a Z7 II (FX and DX) or D850 (FX and DX) so I tried four cameras Z7 (FX and DX) and Z7 II (FX and DX) and got the resulting graph which drops one camera, the Z7 II DX. Anyway the graph link in this post show what I wanted shown. 

[Netr]

If you view an image at a standard size from both the FX and DX parts of an FX camera, you have had to magnify the DX capture more than the FX capture. So any noise at the pixel level is magnified too, even though the pixels are the same size.

Dynamic range is the difference between the lightest and darkest tones in an image. Because noise comes in random colours, noise makes the lightest tones darker in DX compared with FX, and the dark random noise means your tone is less bright. Similarly the darkest tones are a bit lighter in DX compared with FX for the same reason, because of the white noise in this case. So in DX, the range between white and black is lower - usually about 1 stop of exposure different.

[Jack Dahlgren]

The physics of the sensor is the same for both. The photonstophotos site normalizes everything to the same final print size. While this may be practicable in certain situations, I believe it conflates too many aspects of the process and it is confusing. For example, if you crop an image have you reduced the dynamic range of the camera? To me this is similar to people using 35mm “equivalent” focal lengths.