Which ISO setting for long exposures?

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I was a film photographer/printer for 35 years and finally bit the bullet and got a Z 6. I've noticed that many photographers who shoot long exposures prefer to use an ISO of 100, often for 30 minute + shots. Why not use a higher ISO for a shorter exposure? Is there something about the lower ISO that is beneficial in post processing?
 
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What Mike said, but it also has to do with what you are looking to accomplish. Silky flowing water comes to mind. Higher ISO and shorter shutter speed and you might not have silky water.
 
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We all strive to lower ISO
In wildlife photography high iso can ruin feather detail. Software like Dx0 can fix some but it’s better to min iso
 
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Also something to think about, each camera has a “base iso” where the camera is designed to provide the cleanest shot with the most dynamic range. The new z6 base iso is 100 where as the z7 is 64. Probably not too relevant to the question posed but food for thought.
 
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each camera has a “base iso” where the camera is designed to provide the cleanest shot with the most dynamic range. The new z6 base iso is 100 where as the z7 is 64.
If all other factors are equal, is there any evidence that a camera with a base ISO of 64 produces a noticeably better image than a camera with a base ISO of 100?
 

Growltiger

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If all other factors are equal, is there any evidence that a camera with a base ISO of 64 produces a noticeably better image than a camera with a base ISO of 100?
Some sensors do not produce completely noise free images even at base ISO. These sensors can indeed benefit from using their low ISO setting (i.e. lower than base).

But your question is asking to compare two different sensors, which have different base ISOs. It cannot be answered as every sensor has many differences and it would depend also on whether they were made by the same company, what technology level they are at, etc.
 

Growltiger

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I'm surprised that at least in the lab when a sensor is under development that two sensors are exactly alike except for their base ISO.
The Base ISO that is quoted is really a compromise between image quality (low noise) and dynamic range. If you set it too small you lose dynamic range. By allowing "low ISO" settings the camera makers allow the user to decide.
 
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If all other factors are equal, is there any evidence that a camera with a base ISO of 64 produces a noticeably better image than a camera with a base ISO of 100?
I believe growltiger already answered this for you but basically it’s like comparing apples to oranges. Sensor design takes into account the base iso. There isn’t necessarily any evidence that I am aware of that all things equal a sensor with a lower base iso takes cleaner photos; that being said though ISO function is in its most basic form an amplifier and the less power applied to the amp the cleaner the signal. 64 vs 100 is what, around 3/4 stop? All interesting conversation I like it.
 

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