It would take a rather brightly lit room to get your ISO down that low. I've got a low hanging, 5 light fixture in a small white room and I just metered f/3.2, 1/60 and ISO 1250. So, bright sun is definitely going to help, but ISO 200 or 100 inside, at f/3.2, without flash is an impossible dream.

You either need a faster lens (like a f/1.4) - but that is going to require some razor thing depth of field probably by setting it really low. Or you need a flash. If you haven't used a 'real' flash before - they have a bad rep till you get to know how to use them either bounce-style or off camera.

If you really want to shoot that low ISO inside, get a flash. Its well worth the investment.

But frankly, a Canon Mark III shooting at ISO 640 is completely fine. The noise really should be fine for a Full Frame camera at 640. Of the things to worry about, I wouldn't cry too much about it.

It would take a rather brightly lit room to get your ISO down that low. I've got a low hanging, 5 light fixture in a small white room and I just metered f/3.2, 1/60 and ISO 1250. So, bright sun is definitely going to help, but ISO 200 or 100 inside, at f/3.2, without flash is an impossible dream.

You either need a faster lens (like a f/1.4) - but that is going to require some razor thin depth of field probably by setting it really low. Or you need a flash. If you haven't used a 'real' flash before - they have a bad rep till you get to know how to use them either bounce-style or off camera.

If you really want to shoot that low ISO inside, get a flash. Its well worth the investment.

But frankly, a Canon Mark III shooting at ISO 640 is completely fine. The noise really should be fine for a Full Frame camera at 640. Of the things to worry about, I wouldn't cry too much about it.