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X-T2 and Auto ISO

KMLNewYork

By KMLNewYork
in Fuji X-T2 / Fuji X-T20

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KMLNewYork Apprentice

KMLNewYork

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Posted

This past week when taking pictures in full sun using a 50mm f/2 in aperture priority mode and auto ISO, I found that the camera would set the ISO to 400 even though the shutter speed went as high as 23,000. On some photos the ISO was set to 200 but I could not determine why it set some to 400 and some to 200. Does anyone have any ideas as to why this happens?

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pete1959 Collaborator

pete1959

Posted
Posted

Were you at F2?

 

Full sun @ f2 is tough, so to speak, on the ability of the camera to expose.

 

Simply put, that's freaking bright out @f2.

 

Even at 2.8

 

If you are wide open or close to it:

 

The camera/metering system is floating the ISO to it's lowest allowance in RAF, ISO 200.

 

I'm guessing wide open at F2 on a bright sunny day has got you well into electronic shutter...

 

A bright sunny day @ ISO 200 at F2 is a shutter speed of 1/12,800 which is beyond the mechanical shutter of 1/8000th (using the old bright sunny day rule of 1 ASA at f16)

 

You are on the outer limits of what the camera wants to do so it starts floating the ISO starting at ISO 200 and then 400.....in your case only one stop....which is wholly accountable and likely due to variances in what you are exposing on, as the previous poster indicated.

 

Regardless the one stop float is not that much, it's just that you are already at the extremes wide open on a bright sunny day.

 

ISO 200 is full blown as low as she goes :-)

 

So the camera is trying to do what it decides to do, rather than changing your shutter speed it's floating the ISO off of the base of 200.

 

That's my 2 cents on what the camera is doing.

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