M9 auto iso

[TonyField]

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Am I correct in saying that the auto-iso feature only works properly with manually set shutter speed? For example, if you set the max-iso value to 640, then setting the shutter speed to, say 1/250, the iso will be adjusted higher and higher until the 640 max is reached depending on light levels and maintain "correct" exposure. Subsequently, lower light will cause "under" exposure.

 

In auto-exposure mode, the camera will automatically adjust the iso up to the maximum value provided, however will use a maximum shutter speed as set up in the firmware, but will reduce the shutter speed as needed to achieve "proper" auto-metered exposure in low light. This will set the shutter speed to, say, 1/125 second (as set in the firmware), increase the iso to say 640 as the light drops but the shutter speed stays at 1/125. Subsequently, with even lower light, the shutter speed will reduce to maintain auto-exposure even dropping the shutter speed 1o 1/10 second or longer as need..

 

This is what I have found by experimentation. If this is true, I really think the "auto-exposure" with "auto-iso" is improperly implemented. With manual shutter speed set, it works as expected.

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[Luke_Miller]

I believe you understand correctly how Auto-ISO functions on the M9. But I also believe it is properly implemented. The "A" on the shutter speed selector stands for Aperture Priority. Aperture Priority is a form of auto-exposure and by selecting it the user is telling the body "I don't care about shutter speed - just produce a correct exposure using the aperture I've selected." Every camera I've shot with that offers Aperture Priority will use the full range of shutter speeds to achieve proper exposure.

 

When Auto-ISO is added to the mix nothing really changes in that regard. The Maximum ISO ceiling and Minimum shutter speed floor settings apply only to the Auto-ISO function. So if in the Auto-ISO menu I set max ISO to 640 and minimum shutter speed to 1/125 - the ISO will be automatically set at some value between 160 and 640 in order to allow Aperture Priority to keep the shutter at 1/125 or higher. Once ISO 640 is reached and light levels drop further Aperture Priority will use whatever shutter speed necessary to achieve proper exposure just as if I had used fixed ISO set to 640.

 

If a minimum shutter speed of 1/125 is a requirement, setting the shutter speed to 1/125 gives you that as you have discovered.

[Berth]

I use both manual shutter and manual aperture with auto-ISO on my M-E. It works extremely well for me, giving me control over both depth-of-field and subject sharpness.