Digital lets you shoot in manual mode and yet still be in auto

Fuji X-E2,  XF 55-200mm, ISO 3200, ƒ/8, 1/1000

I was shooting some photos of birds on our bird feeder when I realized I wanted a little more depth-of-field than wide open at ƒ/4.8, so I closed down the camera to ƒ/8.  This made it possible to keep the bird in focus.

In Aperture Mode then the camera would normally drop the Shutter Speed to low to freeze the birds and it to look in focus. See the bird feeder is hanging and would swing a little as the birds would land.

Now if I choose Shutter Speed Mode and picked 1/1000 the camera would open up the aperture which isn't what I wanted.

Now in film days you would typically not get this photo, because I would normally have put ASA 100 [ISO 100] since the photo was in sunlight. You would be stuck with whatever ISO you had put in the camera, but today with digital this can change frame to frame.

AUTO ISO

The thing I love the best about digital is the Auto ISO. In this situation I then put the camera in Manual Mode and pick the ƒ/8 and 1/1000 and the camera's Auto ISO will now pick the ISO that gives me a well exposed photo.

Fuji X-E2, XF 55-200mm, ISO 3200, ƒ/8, 1/1000

The Fuji X-E2 Auto ISO

When you choose the Auto ISO on the camera the camera automatically chooses a sensitivity between the default and maximum values. Sensitivity is only raised above the default value if the shutter speed required for optimal exposure would be slower than the value selected for MIN. SHUTTER SPEED.

If the value selected for DEFAULT SENSITIVITY is higher than that selected for MAX. SENSITIVITY, DEFAULT SENSITIVITY will be set to the value selected for MAX. SENSITIVITY.

The camera may select shutter speeds slower than MIN. SHUTTER SPEED if pictures would still be underexposed at the value selected for MAX. SENSITIVITY.

I have set my AUTO ISO to have a range of 200 to 6400. The one thing I do go in change regularly is the minimum shutter speed.  I have it set for 1/500 sometimes for quick moving subjects and then maybe change it to 1/60 for inside more fixed subjects.

If you need to control the Aperture and Shutter Speed to get the photo, then let the ISO climb higher. with today's sensors the higher ISO isn't as noisy as in years past.  I think you will agree that the photos above, which are cropped are acceptable noise for shooting at ƒ/8 and 1/1000.