# LOW ISO settings in Nikon D90



## Shiva_42

I'm fairly new to DSLR's, so forgive me if this is an ignorant question:

The normal ISO sensitivity range on my D90 is 200-6400 (or something very close to that).  Now, I can accurately imagine the potential issues if I artificially increase my ISO to HIGHER that the top value, but what is the potential downside of LOWERING my ISO for a shot?

I.E., I want to take a landscape shot in bright sunlight, but want some movement in the water in the pic, so I REDUCE my ISO to 100.  What is the disadvantage of shooting my pic with this setting no longer on automatic?


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## mwcfarms

Shiva_42 said:


> I'm fairly new to DSLR's, so forgive me if this is an ignorant question:
> 
> The normal ISO sensitivity range on my D90 is 200-6400 (or something very close to that).  Now, I can accurately imagine the potential issues if I artificially increase my ISO to HIGHER that the top value, but what is the potential downside of LOWERING my ISO for a shot?
> 
> I.E., I want to take a landscape shot in bright sunlight, but want some movement in the water in the pic, so I REDUCE my ISO to 100.  What is the disadvantage of shooting my pic with this setting no longer on automatic?



Do you mean your shooting a landscape with water and want the water to look soft and flowy, silk like. Adjusting your ISO won't affect that look. ISO has to do with light sensitivity. Your shutter speed should be what your looking at. ISO can effect your shutter/aperature speed combinations to gain correct exposure though.


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## jake337

I think I understand what they are asking but don't know the answer either. The OP seems to be saying he wants to use LO1 iso setting on his camera so he can DROP his shutterspeed to getting the water looking silky. Maybe the situation was very bright and he needed to drop his shutter speed lower some more.

High ISO's introduce grain. Is there any negative effect of using Lo.1 (iso 100) on a D90 or any other brand camera for that matter.


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## mwcfarms

jake337 said:


> I think I understand what they are asking but don't know the answer either. The OP seems to be saying he wants to use LO1 iso setting on his camera so he can DROP his shutterspeed to getting the water looking silky. Maybe the situation was very bright and he needed to drop his shutter speed lower some more.
> 
> High ISO's introduce grain. Is there any negative effect of using Lo.1 (iso 100) on a D90 or any other brand camera for that matter.



I wasn't sure about the negatives but I did find this on a search for the topic.

Flickr: Discussing New d300s owner has a question about ISO in Nikon D300s Users Group


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## KmH

Shiva_42 said:


> so I REDUCE my ISO to 100. What is the disadvantage of shooting my pic with this setting no longer on automatic?


You will lose dynamic range.
Dynamic range describes the range between the brightest and darkest light your image sensor can record with each exposure.

In the native ISO range 200 to 6400, the image sensor sensitivity is adjusted in the image sensor amplifier circuits.

When you go below or above the native ISO range, and into the Lo 1, Lo 2, and Hi 1, Hi 2 setting the image sensor sensitivity isn't actually altered, the apparent new ISO is accomplished with software.

That is why dynamic range is lost.


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## Shiva_42

Thanks Dee and Keith.  I looked at the other discussion pertaining to this issue...

Yes, coming from a long-time film background, my favorite film was the traditional Fuji Velvia (asa 50), so I was just daydreaming about why the lower ISO would be a detriment, instead of an asset.

I fully understand the loss of dynamic range, and obviously can achieve the look I'm after with a variety of different approaches.

I was simply curious, and these explanations were perfect!  Thanks so much!


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## jake337

so i will lose dynamic range, well i guess Lo1, 2, 3 are out the door


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## Robin Usagani

Sometimes when you want to shoot with aperture wide open (f/1.4 or something), you cant do it when it is pretty sunny.  Being able to go lower than 100 is a huge plus!


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## Patrice

It's true that going below base iso reduces dynamic range in some circumstances so the safest way to photograph a bright scene at low shutter speeds is to use a neutral density filter. They are available in a variety of f-stops.


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## Patrice

> In the native ISO range 200 to 6400, the image sensor sensitivity is adjusted in the image sensor amplifier circuits.



The photocells on the sensor output an electrical signal when it receives photons. That signal is regulated by the amount of photons in a given time period. Nothing else regulates it other than changing the amount of photons that are let through the lens to reach the sensor. The electrical signal is an analog signal. In changing the iso away from base iso the signal is either amplified before or after the analog to digital converter. Some cameras use an analog amplifier within a certain range of iso's and then switch to a digital amplifier for lo1, hi1 and such like iso settings. You can determine your particular camera's way of doing it by looking at the hexidecimal output of the sensor data. A balance between even and odd numbers indicates an analog amplifier. Predominantly even numbers indicate a digital amplifier.

The iso's other than base in the 'native iso range' alluded to in your iso settings are all amplifications of the base signal. Your sensor has only one sensitivity and so one iso. Everything else is a circuit or software manipulation. Changing the iso value on your camera settings does not change the signal generated by the photocells - only how much amplification you submit that signal to.

There are cameras, such as D7000 and D3s, that have exceptionally efficient sensors and very clever amplifiers that give us a very broad range of usable apparent iso but even they are single iso machines. You will always have the lowest image noise at base iso.


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## Garbz

Almost 100% spot on. Depending on the design of the amplification step it is possible to alter the signal on the photocells when changing the amplifier. The reason is photosensors are loaded by the following stage and the design of that stage will cause changes in bias and slight changes in performance. (not slight). 

It's similar to guitar pickups. You can completely change the sound of a guitar pickup by changing the design of the amplifier without actually changing characteristics of the amplifier itself (i.e. two amplifiers each with the same gain and harmonic distortion load the pickup differently)

But in reality the differences are slight for photosensors.


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## klakf

In response to the person who is trying to get soft, silky looking water flow, one thing that has really helped me is using a neutral density filter. It takes off that high highlight in the water that is reflecting the sun and allows your meter to better do its job. The way to get soft flowy water is to set your camera for a long shutter speed, and using a tripod is a must.


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## Garbz

If they really wanted soft water I think after a year from when they originally posted they would have figured it out


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