Quote Originally Posted by Chuck Lee
Not at the same shutter speed and aperture
as ISO 160.

Agreed. I should have clarified that I meant a different exposure.


Quote Originally Posted by Chuck Lee


You would have to shoot ISO 100 at -.7ev to get the same
speed/aperture combination. I'm willing to sacrifice a whole 1/3 stop
or DR for that. The real world result is that I canhandhold at1/125th
rather than 1/80th shutter speedand geta cleaner and possibly
sharperimage.

Me too. I only use ISO 100 when I have plenty of exposure to spare. (1/3 stop is such a small difference anyway.)


Quote Originally Posted by canoli
Which 'tweener ISOs are less bad and which ones should be avoided?

The "minus 1/3" ISO (160 320 640 1250) are fine, the "plus 1/3" ISO are suboptimal (125 250 500 1000). Everything above ISO 1600 is suboptimal.


Quote Originally Posted by canoli


One more question - is any of this relevant to amateur photography?


It's a pretty minor effect by itself. Just like HTP is a pretty small effect, and ALO is a pretty small effect. But when you start combining all these small factors, it results in a big factor. For example, ISO 250 by itself may not increase shadow noise enough to notice. And ISO 200+HTP by itself may not either. But combine 250+HTP and the result will be much more noticeable: the shadow noise is as bad as ISO 640. Add ALO into the mix and you can get people wondering why their ISO 250 shot looks like ISO 1600.