ISO Lo1 setting

FLIGHTO

Senior Member
I have had the D500 since November. I have recently been doing a lot of long exposure sea scapes. In attempts to block as much light as possible for daylight long exposures, even with an 8 stop ND, I ventured into the Lo ISO settings. I have to say that the camera takes beautiful images at these settings with good DR.... what am I missing? Why are these not native settings?

Even with comparison frames shot at ISO 50 and ISO 100 I am not seeing any difference outside of noise.... I guess I am psyching myself out because they are not native???? Can someone explain the technical side of this?

Much appreciated..


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Fred Kingston

Senior Member
I recently ventured into the same area testing sun shots for next week... I didn't do any comparisons but LR sees my D600 as being at ISO 50 when using the non-standard settings... I'll be interested in seeing further discussion...
 

Blacktop

Senior Member
I recently ventured into the same area testing sun shots for next week... I didn't do any comparisons but LR sees my D600 as being at ISO 50 when using the non-standard settings... I'll be interested in seeing further discussion...

I venture below the native ISO setting when my ND filter (or if I forget my ND filter) is not enough for a daytime long exposure. For regular exposure shots I still use the native ISO however.

It doesn't seem to suffer in my opinion.
 

Fred Kingston

Senior Member
I guess the next question is... going from the standard ISO of 100 to the Lo.1 setting seems to be ISO 50... and is that Lo.1 a true 1-stop difference in EV
 

lokatz

Senior Member
Nikon uses Lo settings on many models, with different ISO ranges. For instance, the D5/500/600/750/800/7500 share the Lo-1.0 (ISO50) to Lo-0.3 (ISO80) options, while the Df/D300/700/3/4 have Lo-1.0 (ISO100) to Lo-0.3 (ISO160). The D810 (but not the 810A) even goes from Lo-1.0 (ISO32) to Lo-0.3 (ISO50).

At very low light intensity, semiconductor photo sensors tend to become non-linear: when you cut the light in half, the photonic energy the sensor records becomes proportionally even less than that. This is why with very long exposure times you tend to get underexposed images - at very low light, closing the aperture by a factor of 2 can no more be fully compensated by opening the shutter twice as long.

My guess is that Nikon chose the Lo denominations to hint at this effect and defend themselves from claims that these ISOs are not accurate enough. Not sure about this, though.
 

WayneF

Senior Member
I have had the D500 since November. I have recently been doing a lot of long exposure sea scapes. In attempts to block as much light as possible for daylight long exposures, even with an 8 stop ND, I ventured into the Lo ISO settings. I have to say that the camera takes beautiful images at these settings with good DR.... what am I missing? Why are these not native settings?

The DR is less though, however it might still be generally adequate.

The camera sensor has one ISO sensitivity, often ISO 100 in most models. That is how much light (photons) is collected in the sensor cells.

Then higher ISO multiplies these values to shift the histogram right, up brighter. That also boosts the low level noise higher too, to be seen much better. This part is easy to understand.

The lower ISO method divides the sensor values, shifts the histogram left, down. That shifts noise off of the low end reducing noise (what there was of it at ISO 100 native). This shift down leaves blank empty space at the top of histogram, which is reduced DR, not utilizing all of the space that could be possible. Contrast and DR are similar but inverse things (the difference in bright and dark values). Contrast is higher due to reduced highlights. This simply does not meet the specifications for ISO, and Nikon does not call it ISO (instead calls it LO 1, etc).

The histogram data is shifted for LO and HI (or any ISO higher than 100), but this exception does not show, nor cause clipping. Before it is stored, the histogram shown to us is also adjusted to "hide" the shift, it looks normal to us. But it has been manipulated.

The D500 manual page 124 says LO 0.3 - LO 1 is "equivalent" to ISO 80 - 50 (speaking of sensitivities), but says contrast is higher than normal, and clearly says ISO 100 or higher is recommended.

Doesn't mean it won't work for your use though.
 
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FLIGHTO

Senior Member
Interesting. I am gonna test this some more this weekend. I haven't been specifically looking at the difference in contrast between 50 and 100..... I will now... I appreciate the info.


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