A100 Auto ISO

[Michael McCullough]

When experimenting with bright subjects, clouds specifically, using Aperture Priority and F stops from 4 through 6.3 and Auto ISO, the shutter speeds display in the 1/1000 to 1/250 range. I would expect the LCD to show correspondingly high ISO's. However, the ISO display shows "Auto" and 100 for all images no matter how over exposed. Same for the histogram. The Sony operator's manual is no help nor could I find any detailed information online as to how the Auto ISO actually displays information. Note that I am experimenting with such settings and subjects simply to learn how the camera works and do not save the images after studying the effects. Any feedback would be appreciated. 

[michelb]

The owner's manual mentions this:

When ISO is set to (Auto), the ISO sensitivity is automatically adjusted between ISO 100 and ISO 800, however if the Mode Dial is set to M, it is fixed at ISO 100.

 

My opinion about this: With bright subjects, Auto ISO will probably remain at 100 until shutter speed decreases to the point that Super Steady Shot can not handle it. So any shutter speed that is faster than 1/focal length is likely to remain at ISO 100 until that 1/focal length becomes difficult to handle by SSS to allow a shutter speed that is capable of providing reasonably sharp pictures.

 

[Michael McCullough]

Thanks for your prompt reply. In other words, in the very bright conditions I was experimenting with and when using AUTO ISO,  Aperture Priority and, say, a 40 mm focal length I should expect to see ISO 100 in the LCD until the shutter speed becomes too slow to be compensated for by the SSS.  This would of course apply to handheld.  However, I was using a tripod with the SSS disabled for all images regardless of F stop.  That said, I suppose  the ISO value shown on the LCD was not the actual value set by the AUTO feature when the aperture was opened up to F 5  and the shutter speed was 1/1250, even though the LCD still read ISO 100. I have a second A100 and will repeat the experiment. If the information on the LCD regarding ISO remains the same under similar conditions, then it must be a design feature. 

[michelb]

Your camera ( and i guess all cameras ) has no idea you are on a tripod and my guess is that at any shutter speed faster than 1/40 sec. for a 40mm lens Auto ISO will probably go to ISO 100 automatically. 

 

This feature is likely more useful in low light where you need a reasonably fast shutter speed to prevent blurry images while still getting low noise (and that is likely why it is limited to ISO 800)

[Michael McCullough]

Between the two above replies, I think I understand how the system works. Thanks.