Nikon D90 ISO

[David Bottel]

I have a Nikon D90 which has a native ISO range of 200 to 3200.
This range can be extended both at the low end and at the high end.
I know that increasing the ISO introduces noise,but are there any issues when the ISO is lower than the native 200.

David

[Dave Humphries]

Hi David,

That's something I have wondered about - I just read the manual for my D5000, which uses the same sensor.

It is very vague - it says "Contrast is slightly higher than normal; in most cases, ISO sensitivities of ISO 200 or above are recommended" So that's not a lot of help!

I really don't know why they do it this way at the low end, I wish they'd explain what it does, or be more specific under which circumstances it shouldn't be used.

I guess the alternative is to lose light by optical means, but if you want to shoot pin pricks of bright lights in a dark scene, adding say an ND, or especially a CPL, could cause worse problems with reflections and flare.

So, I'll await an answer too,

[Dave Humphries]

Further research (aka googling);

This post provides an answer, how accurate it is I wouldn't know, although sounds plausible.

Another thread, which I won't link because I found it too confusing, did say the Lo (and Hi) settings were achieved by 'shifting the bits' after the Analogue to Digital Converter (ADC), rather than by analogue gain variation before the ADC, in theory this loses a stop of dynamic range which I guess with some subjects, you wouldn't notice. However, it also ended with the analogy that using Lo and Hi was like using digital zoom over optical zoom, which as we probably all know, is a bad idea.

The 'bit shifting' idea is what I had heard before, but again, how true it is, I wouldn't know for sure.

Personally I do avoid Lo and run at 200 iso when there's enough light, but my normal is more likely to be 400 or 800, but that may be caused by my not having many 'wide' lenses.

Cheers,

[David Bottel]

Dave,
Thank you for your reply.
I guess like you I'll stick with ISO 200 as a minimum for now.

David

[sleist]

Further research (aka googling);

This post provides an answer, how accurate it is I wouldn't know, although sounds plausible.

This thread echos Thom Hogan's discussion on the topic in his e-book on the D90. If you must use it, he suggests under exposing by -0.3 EV and avoiding hi contrast scenes/subjects.

[Clactonian]

These are the results from the DPReview test of the D90 which would bear out Dave's comments


Sensitivity Shadow range Highlight range Usable range
ISO 100 (Lo 1) -4.6 EV 3.0 EV 7.6 EV
ISO 200 -4.4 EV 3.9 EV 8.3 EV
ISO 400 -4.8 EV 3.9 EV 8.6 EV
ISO 800 -4.5 EV 3.9 EV 8.4 EV
ISO 1600 -4.8 EV 3.9 EV 8.4 EV*
ISO 3200 -5.4 EV 3.9 EV 8.4 EV*
ISO 6400 (Hi 1) -7.7 EV 3.7 EV 8.2 EV*

[David Bottel]

Thanks Steve and Mike for your input.

David